Rear Towing Points on an Oka

If you have rear bullbars on your Oka, but no tow bar (we used the rear space for extra fuel tanks), rear towing points can be easily added if you have built in reinforced high lift jack points. This applies mostly to full body models.

Drill a 22mm hole (or whatever size fits your D or Bow shackle pin snugly), just behind the high lift jack points on the side plate of the bullbar frame. The hole should be low enough so the shackle can be lifted to at least the horizontal position.

22mm holes in the bullbar side plate

The D or Bow shackle will fit neatly through the jacking point and provide strong towing points on either side of the Oka.

Bow shackle located on the bullbar

The bullbar side plate is 8mm steel and is bolted directly to the Oka chassis using the same 16mm bolts provided for holding a tow bar. It's the equivalent of the tow points built into the front bullbar and probably stronger. It's also the primary member used by the high lift jack in raising the vehicle.

 

Using D or Bow shackles on both sides and an equalisation strap (or a tree trunk protector), the stresses can be shared and equalised between each bullbar when the Oka is being towed backwards, or while pulling another vehicle or object off a track.

Notes:

 

Shackles with at least a 4.75 Tonne rating are recommended (equivalent to 10,500 lbs). If you need more than this you probably need a crane not a tow truck.

 

A webbing strap will fit a Bow shackle better than a D shackle.

A steel plate or large washer with 22 mm hole could be welded to the side plate to stabilise the action of the shackle if required, or packing pieces can be added to the shackle pin as shown below.

Don't leave the shackles attached whilst driving, the pins will vibrate loose and the shackle will drop off.

Bolt-on tow hooks area available in 4WD shops but they are not as reliable as as D or Bow shackles since you are dependent on the strength of a hook (not a closed steel loop) and the integrity of 2 small bolts. In any case I couldn't find anywhere suitable to mount them.

Fitting Airbags to an Oka

Surprisingly, a search of the Oka Owners Group forum revealed only five references to fitment of airbags to an Oka, (and one of those was mine), plus an article by Peter Furlong from several years ago.

I'm aware of at least 6 Oka's with airbags fitted but I'm sure many other people are toying with the idea.

In the May 2011 issue of the CMCA magazine The Wanderer is an article by Collyn Rivers on "Airbag Characteristics" which makes interesting reading. In an earlier article (Feb 2011) he cautioned that airbags should never be fitted only to either the front or rear of a towing vehicle, citing potential jack-knifing of caravans. (Note you may need to be a CMCA member to access articles from The Wanderer).

 

Having recently fitted airbags to both the front and rear of our Oka, I was somewhat relieved to read Collyn's conclusion that "there is no reason at all not to use air bags if you wish. They are first rate engineering products, but specifying them correctly requires considerable skill and expertise".

In the latest article he explains in more detail implications of adding airbags to a suspension system. He also refers readers to an article on his website (Vehicle Dynamics) which discusses generally how a vehicle behaves on the road. Although much of the emphasis relates to towing and caravan applications these articles are worth reading before embarking on any changes to an Oka suspension.

 

Why Fit Airbags?

I wanted to use airbags for 3 main reasons:

• to shift some (roughly half) of the load off the springs and suspension pins and thus improve their reliability,
• to provide some suspension levelling for differing loads, road cambers and to compensate for spring wear (sag),
• to soften the ride over rough tracks and corrugations, and
•  since we live in the Oka while traveling, being able to level the vehicle at night was an additional side benefit.

Fitting airbags to the rear suspension in 2010 was easier than the front and I'm glad I tackled that end first. On a 14,000 km trip up to the Tip of Cape York they performed well, allowing load levelling and raising the rear as necessary. Passengers in the rear reported a very smooth ride even over quite severe corrugations. It was a very different story in the front however, sitting directly over the wheels, with quite stiff front springs and heavy duty (Ralph) shock absorbers, the ride was shattering over any significant corrugations, and it was that which lead us to install airbags on the front this year, in an attempt to provide a smoother ride as well as the other levelling capabilities.

Individual airbag pneumatic controls is required to get the most benefit from these functions.

Airbag Research

I did as much research as is practical into airbag selection (also called air springs) and reviewed other people's installations. The model we fitted is that recommended for the Oka by the Firestone Airbag importer, The Airbag Man, their part number AB0051. This is a Firestone model 1T14C-1, which defines a family of reversible sleeve air springs. The Firestone Assembly Order Number is W01-358-5311, which defines the specific characteristics of this variant (and there are hundreds of variants). This is also the number to use for an internet search.

The metric datasheet can be found here and the imperial version here. A brief explanation of how an air spring works is here and a full Engineering Design Guide can be found here. There are other manufacturers of airbags, notable Goodyear, but most applications seem to use Firestone.

For some insight on airbag failure modes see this Goodyear document and scroll down to page 168. Over-extension, chemicals, corrosion, impact and abrasion are the most common causes of failure (can there be many others?). This site shows the failure modes for airbags fitted to a Range Rover.

Driver side front airbag fitted. This was the trickiest due to the studs on the diff housing.

Airbag Calculations

The W01-358-5311 model has an internal buffer, so it can be used to replace the standard Oka Aeon rubber bump stops, (although in normal operation the internal buffer would hardly get used so it's prime function would be to protect the airbag from damage though over-compression) and has a design height of 255-260 mm which is just what an Oka needs (roughly the space between the top of spring and the chassis bump stop mount). This model can be used from about 160 mm to 320mm operating height but at 260 mm, it's in the design centre of both it's height range and air pressure range of about 3 to 5 Bar (40-60psi), which is load dependent.

In a very simplistic calculation to verify this assumption, for an Oka at 5500kg, each spring carries roughly 1000-1200kg (allowing for the unsprung axle/spring/wheel weight), with probably more at the rear than the front. To support half this load requires the airbag to support about 500-600kg at it's normal operating height. From the Firestone datasheet, at this load and 260mm height, the internal air pressure required is around 3-4 Bar (40-50 psi) which is in the centre of its operating range of .7 to 7 Bar (10-100 PSI). Collyn Rivers in his article notes that the best airbag operation (soft ride with impact absorption) is over the lower 40% or so of it's pressure range, so on that basis we are about right.

Note of caution: at maximum pressure and/or operating height, these airbags could spread the spring/chassis separation distance to a point which might over-extend the length of a shock absorber. This could lead to a mechanical failure somewhere. It's unlikely to occur in practice if the vehicle height is kept within normal bounds but I suggest keeping airbag pressures down to 20-30 psi when the Oka is lightly loaded (eg between trips) to avoid this. Taking weight off an airbag quickly allows it's height to increase unless the air pressure is also reduced (Boyles Law).

Source of Supply

You can buy these airbags from The Airbag Man, or their distributors (eg Air Springs SA , which is what we did for the first 2), or from any number of US on-line stores eg TruckSpring.com (which where went for the last 2 at a considerable saving (more than 50%, even after the addition of freight) or SDTruckSprings.

Genuine Firestone pneumatic controls and gauges are also available from the same US suppliers but we found a local supplier Air Ride Suspension in Sydney who was almost as competitive, so we supported them. They can also supply the air pipe and push-fit connectors (which are very quick and effective).

A dual pneumatic control panel. Two are needed for individual control of 4 airbags. There are individual air switches and a dual needle pressure gauge (white and yellow needles).

Planning the Project

Fitting airbags is not a trivial task as it requires a fair amount of steel fabrication and assembly, to design and manufacture the top and bottom plates to support the airbags and to meet the physical peculiarities of the Oka, and to align and attach them securely to the springs and chassis. For a tough, off road vehicle, this certainly requires a lot more than "just bolt the top and bottom plates on" concept shown in the Firestone installation video.

Neither is it a cheap exercise, an airbag will cost from $200-400 each, depending on the source (US/Aust), and a dual control panels are $150-200 each, so the total for 4 airbags with individual controls is around $1500. It is possible to pay more, by fitting an all-electric system of electrically controlled valves for each airbag. This allows the system to be controlled by electrical, rather than pneumatic switches, or an automated electronic levelling system, like a Winnebago.

Much useful practical experience was gained from David Hallandal's airbag installation, and I appreciate his help and assistance with this, and I also located several web photos of other installations to analyse.

Top and bottom steel plates must be mounted to the Oka to provide flat platforms for the airbag to operate between, and be attached to. The top plate is attached to the chassis via the bump stop bracket after the Aeon rubber buffer has been removed. The bottom plate is attached to the spring clamp.

Fitting the rear airbags is the least challenging and there are several ways of supporting the top and bottom plates. Apart from ensuring reasonable alignment of the top and bottom plates (and Firestone claim that they are quite tolerant to misalignment of up to an inch either way), the challenge is primarily the design of the mountings so that they can actually be assembled on the vehicle.

The airbag piston (the large aluminium casting supporting the rubber bag) is sandwiched between the airbag and bottom plate by a single centre bolt into the airbag. This is fitted up from underneath the bottom plate and needs to be a countersunk head bolt since it will be located on top of the spring clamp. The piston has no fixings of its own.

The fixings for the top of the airbag comprise 2 captive tapped holes and an air inlet hole. The top plate needs to be designed so that the bolt holes are accessible for insertion of the bolts when the top plate itself is fitted to the bump stop bracket, while allowing the air inlet connection to be accessible for connection of the air pipe.

A 25mm spacer is also required so that the top plate clears the chassis frame, and a countersunk bolt is needed to fix the top plate to the bump stop bracket since its head will be located directly above the airbag.

Here are a few Installation Techtips transcribed from the Firestone Web site. Click on the headings to go to the Firestone website.

Here are a few quick tips to make the installation of your air helper springs and air accessories correct and ensure proper operation of your system.

Air Spring Alignment

Air Spring alignment is important to the operation of your air helper spring kit. Upon installation, visually align the air spring. There is no need to use a level or other measuring device because the air springs are very forgiving, if it's off a fraction you should be fine. Most kits allow for movement of the upper and lower brackets to assist in making the air spring vertical. Position the brackets so the upper and lower brackets are parallel. The most important item to consider when placing the air spring is design height. As long as the proper design height is maintained and the air spring is as vertical as possible your kit will provide you with years of service.

Push-to-Connect Fittings

Firestone's push-to-connect fittings are extremely easy to use. Once the length of air line has been selected to span the distance from the air springs to the inflation valves simply use a sharp knife to cut the air line as square as possible (DO NOT use hand cutters or other devices that may deform the end of the air line) then push the air line into the fitting as far as possible. That's all there is to it.

Air Spring Clearance

After installing your air helper spring kit make sure you have at least 1/2" of clearance around the entire air spring. A good rule of thumb is to use the thickness of your hand and feel around the entire air spring if you hand comes in contact with an object on the vehicle you may have a problem. If the object can be moved relocate it if it cannot contact Firestone for further assistance.

Mechanical Design Summary

I used 5mm steel plate for the top and bottom plates although you could use 6mm plate or buy universal plates from airbag suppliers already drilled. They would still need mounting arrangements fitted though, as there are no plates commercially available which directly suit the Oka.

With the top and bottom plates manufactured, the basic sequence of assembly is:

Attach the top plate to the bump stop bracket using a countersunk bolt, and aligning the airbag top fixing holes,

Fit the air connection to the top of the airbag (use a swivelling 90º push-fit connector),

Attach the airbag to the top plate using bolts down though the top plate into the 2 captive nuts (after fiddling the air connection though its hole),

Attach the bottom plate to the airbag using a countersunk bolt up though the piston, aligning it radially so it fits the chosen spring clamp arrangements,

Ensure the air connector is not blocked off and pull the airbag down, allowing it to expand, (but DON'T use air pressure, you could crush fingers or break something) and bolt the bottom plate to the spring clamp,

Fit the air pipe and connect up the air supply and controls.

It sounds easy but the devil is, as always, in the detail.

Rear Airbag Development

The bottom plate is probably the easiest to start with.

Assuming the U-bolts and spring centre bolt don't protrude above the level of the spring clamp (if they do they will need to be cut off or clearance holes cut in the plate), the plate can be designed to rest on the centre of the spring clamp with supporting out-riggers welded on which rest on the wings of the spring clamp. The plate can be held on by bolts (high tensile to survive vibration stress) down though the wings of the spring clamp (the bolts need to be positioned carefully so their heads don't foul the outer edge of the airbag piston) or up though the wings of the spring clamp into tapped holes on the bottom plate (be careful of the depth). For bolts hidden under the piston, assuming they don't foul the insides of the piston, their heads could be welded on to the bottom plate.

Rear airbag bottom plate, viewed from underneath. The horizontal bars rest on the spring clamp wings.

Other fixing methods could also be devised by attaching brackets to the spring clamp. The Firestone suggestion of using clamps around the spring pack is not desirable as it can bring unfortunate results.

Clamps around the spring pack can slip. This photo of NT001 is from the "Suzi and Rudi on Tour" website. The airbag was apparently undamaged but the mounting arrangements had to be redesigned.

Note that access to the U-bolt nuts will probably not be possible after fitting the airbags (although you might be able to provide access holes though the plates for some, but not all of them), so ensure they are fully tightened before doing any design or assembly so things can't move. Subsequent checking of U-bolt torque will necessitate jacking up the chassis, releasing the air pressure, unbolting of the bottom plates and raising the airbags out of the way to provide access to the nuts. The airbags don't have to be removed completely.

The top plate needs to be mounted to the bump stop bracket via a 25mm spacer so that it clears the bottom of the chassis rail. A long countersunk bolt can be used for this and I chose to weld its head on to the plate since it won't be accessible once the airbag is bolted on, but that's not essential. Alternatively, a bolt could be inserted downwards through the bump stop mounting bracket into a tapped hole in the top plate (be careful of its depth). Holes will be needed to attach the airbag to the plate and will have to be arranged so that the air inlet connection is accessible. One hole will probably go through the bump stop bracket, which is a good thing as it prevents the plate rotating in service.

My top plate with the spacer block and completely OTT strengthening ribs

For the 25 mm spacer, I welded a steel box to the top of the plate. A couple of thick steel blocks would do but are heavy, like the cylindrical block removed from above the bump stop rubber. I have seen photos of round cylinders or square tube used for this purpose (see below), which might simplify the design, but I preferred a more substantial arrangement. I probably went overboard by welding strengthening ribs to the top of plate as well but this can cause the plate to warp.

Rear airbag top plate trial fit. The square spacer block is needed to clear the chassis rail and the round spacer is because the bolt was too long. Roughly shaped rear top plate, view from below Alternative rear top plate spacer ideas:

 

 

Alignment of Plates

Alignment of the top and bottom plates can be problematic. The location of the airbag is governed mostly by the position of the top fixing holes which are in turn constrained by the chassis rail and bump stop bracket, but it should be inboard rather than outboard to maintain adequate clearance from the tyre.

Rear airbag trial fit

Using cardboard templates, the approximate centre point of the top of the airbag can be determined. With the spring/chassis spacing at the normal distance of around 260mm, drop an approximate vertical from the centre of the top plate to the spring clamp. This will determine the centre fixing hole for the piston but a misalignment of 1 or 2 cm won't affect airbag operation, after all, springs are flexible items and move around and expand and contract all the time when driving.

The centre fixing bolt should be as close as practical to the longitudinal centre of the spring clamp (I don't like the idea of mounting the airbag to the spring itself) but is unlikely to be central laterally (due to the fixing hole problems) and doesn't need to be. My rule of thumb is that the centre of the airbag should be no further inboard than the edge of the spring. If the airbag is outboard there is a risk of it being abraded by a tyre at full axle articulation.

Front Airbag Development

These are slightly more challenging than the rear due to the proximity of engine components, shock absorbers and steering movement of the tyre. Also, on the drivers side, the stud fixings from the spring clamp to the diff housing get in the way.

[Previously, we also had fitted an additional full length #3 spring leaf to all the springs to provide extra support to the spring eyes and suspension pins and this was in part the cause of our rough ride, and also raised the front of the Oka too much. So before embarking on the front airbag design, I removed leaf #4 from the springs (retaining the added #3 support leaf), to soften and lower them so that about half the load could be taken on the airbag at its preferred height. This was a challenging, finger risking exercise in itself but not directly related to the fitting of airbags.]

As for the rear, if the U-bolts or spring centre bolts protrude above the top of the spring clamp they will need to be cut off and/or clearance holes cut on the bottom plates. However this can't be done for the 2 studs into the diff housing. The thread length could be shortened, or the studs replaced by bolts, but they will still protrude above the level of the spring clamp. Fortunately, the hollow area inside the airbag piston allows it to be located over the studs with adequate clearance, and that will dictate the location of the airbag on the drivers side. When cutting clearance holes in the bottom plate for the studs and nuts, note that the stud spacing is different to the U-bolt spacing.

Apart from that, the bottom plate design can be similar to the rear airbags, except that mounting arrangements will necessitate brackets being welded or bolted on to the spring clamps to allow the plate to be attached.

Drivers side airbag. The diff studs fit under the piston and brackets were welded on to the spring clamps to allow fixing of the bottom plate.

At the front, the top plates are actually a bit easier than the rears, since the bump stop brackets are lower than the chassis rail so no spacer is required. However, the location of the airbag fixing holes and air inlet connection will still require the same degree of design experimentation. The tapped bump stop M12 slug can be used to hold the top plate on via a countersunk bolt but I also welded a bracket on top of the top plate and used a bolt though the inner side of the bump stop bracket for additional stability. This also prevents the plate from rotating in service. Support plates could also be welded to the chassis or bump stop bracket if desired. Note, the 2 bump stop brackets are slightly different in design, the drivers side bracket is wider. (I suspect this was due to the bump stop having to be moved outwards to clear the diff studs).

In my case, on the LHS, I have an air compressor mounted on the engine mount so I had to ensure that it could not come into contact with the airbag. So the LHS airbag is more outboard than the RHS, but still will not come close to the tyre.

Left side front airbag fitted in between the tyre and compressor

Pneumatic Controls

Once the mechanical manufacture and fitting is done (which took over a week of full time work for each of the rear and front systems), the air system can be connected. Obviously a permanent source of air pressure is required but airbags don't require a huge volume of air like tyres do, only pressure up to 100 psi (although in reality 60-70 psi is more than adequate), so an electric compressor would be satisfactory.

For maximum flexibility, individual air controls are preferable but the front and rear pairs (or indeed the left and right pairs) could be commoned up but you would loose the ability for selective levelling. Since I fitted airbags in 2 stages, I bought 2 dual control panels at different times which I mounted either side of the steering column and that works out quite well. However a quad controller is also available but would require more space to fit.

2 sets of dual controls mounted either side of the steering column but there are 5, 1/4 inch air pipes to run though the floor

Running the air pipes to the individual airbags around the chassis, plus one to the compressor, is a bit of a pain. They must be fixed (with tie-wraps) so that they are protected from wear and impact (ie above or behind chassis rails like brake pipes), as the sudden deflation of an airbag could cause handling problems.

I fitted a check valve and tap to the airbag air supply so that the airbag system can be isolated from my main air system and be protected from any compressor failure or maintenance activities. I didn't want sudden suspension changes to occur while working on the compressor system, although this is highly unlikely since the control panel switches prevent release of air from the airbags. A small air tank could also be fitted as a reservoir to maintain the airbag supply.

I leak tested all the joints with soapy water and once fitted, the quick push-fit connectors have never leaked. The control system works well although manipulating 4 controls is a bit of a handful. I connected the rear left and right airbags to the LHS control panel and the front left and right airbags to the RHS control panel. The gauges have dual needles, one white and one yellow. I connected them so that "White is Right" so I can remember which is which.

Potential Problems

When fitting the rear airbags I was initially concerned whether the tyres could ever impact the airbags at maximum axle articulation so I fitted some protective plates, partly to tell if there were any wear points and also to protect the airbag if there was. After the Cape York trip there had been no contact at all so the plates are now redundant. But I did have to re-route the exhaust system so that it was well away from the airbag and fitted a heat deflector plate as well.

Right side rear airbag with protective plates and heat shield

Summary

Fitting airbags has been a long but interesting task. The rear airbags worked well over 14,000 km but I have yet to test the front airbags over any rough tracks. A question still remains over whether stronger or softer shock absorbers work best with airbags and I'll be testing both types on the next trip.

I'm hoping that my calculations and assumptions are correct and that we'll get some significant ride benefit from them, plus improved suspension reliability, as well as overnight motorhome levelling.

Safety, Emergency and Recovery Equipment on our Oka

Apart from the usual recovery gear (jacks, towropes, hub adaptor, spade, sand mats etc) we also carry a range of safety gear and emergency equipment.


An article on our Recovery and Maintenance Equipment can be found here.


An article on our Safety and Emergency Equipment can be found here.


An article on Snake Bite Treatment notes and first aid items can be found here.

Fixing the Leaking Steering Box

As we travelled the rough roads across the Gulf Of Carpentaria from Burketown to Booroloola, we noticed a drip of red oil from the power steering box. Checking the hydraulic fluid level revealed that the level had gone down about 1 inch. There was nothing that could be done on the side of the road except to top up the reservoir and carry on, mindful of the fact that on a Oka, the power assistance for the brakes also comes from the same hydraulic power source as the steering, so a loss of hydraulic pressure could be quite serious.

By Booroloola the leak had got worse and was traced to the seal around the input shaft on the top of the steering box. After a long search, we bought a 4 litre can of fluid from a mechanic in Boorloola, the last fluid in the town it would seem.

[Note: After doing this fix, it appears that that a major steering failure from a leaking seal on the input shaft is unlikely, unless the reservoir runs dry].

Red fluid oozing from the steering box.

On the stretch from Booroloola to Katherine, the leak stabilised but it was still losing about 250 ml a day, but what was worse was that the fluid dribbled down the outside of the steering box and was then liberally sprayed by the wind over the chassis, springs and eventually down the side of the Oka where of course the dust stuck to it, creating a sticky mess. We covered the steering box with a modified wine cask bladder to stop the dispersion of fluid but something permanent needed to be done, which could only happen after got home a month later.

The Fix

The steering box fitted to later Oka's (or as an Oka mod to replace the earlier Kirby-Bishop steering box) is a TRW TAS-30 box made by TRW Torfinasa, Spain. You won't find much data on this model which was fitted to a number of European small trucks. However, it is similar in style and operation to other TRW TAS series boxes so information on the TAS-40 to TAS-85 range is quite relevant.

The TRW identification label.

There are a number of useful TRW articles on their website which document the process of replacing the input shaft seal on a TAS series steering box. Even though none of them specifically relate to the TAS-30 steering box fitted to Oka's, these are the most relevant:

TAS Series Service Manual TRW1108 (more detail than you'll ever need)

Service Procedure TAS100 (On-vehicle repair procedures)

Input Shaft Resealing Instructions TRW800 (Useful descriptions with colour photos)

Replacing the input shaft seal can be done without removal of the steering box and takes the best part of a day, once you have the bits and understand the instructions. There is no need to remove the pitman arm or any other components under the vehicle

In a nut shell, you'll need to:


1) remove the radiator grille and LHS headlight frame, and unplug/move aside any cables which will get in the way,


2) remove the steering column shaft, including the lower UJ. (You can do this without removing the steering wheel housing by slitting the rubber boots to remove them and gluing or clamping them back together later. The metal top clamp and foot can also be cut to aid removal and refitting. Refer to our blog entry here for some details on this),


3) prepare for some fluid spillage (you might loose half a litre or so, it doesn't sound much but it can spread a long way),


4) thoroughly clean the top of the steering box,


5) remove the dust/dirt seal from around the input shaft, it's just clicked into a groove on the input shaft,


6) remove the internal circlip (or flat spiral spring clip in our case) from its slot above the seal,


7) temporarily replace the lower UJ on the input shaft and loosely fit a pinch bolt,


8) disconnect the hydraulic return hose from the steering box (it's the larger fitting and marked "R", see the photo below to ensure you get the correct one) and quickly cap the return outlet to avoid fluid loss,


9) quickly plug the end of the return hose,


10) tie an old piece of towelling around the shaft to contain any expressed fluid,


11) spin the engine for a few seconds but don't allow it to start (disconnect the wire to the fuel cut off solenoid on the injector pump). This builds up pressure in the hydraulic system and pops out the seal. Refitting the UJ prevents it shooting skywards. When you hear a "pop" as the seal pops out, stop spinning the engine immediately to reduce fluid loss.


12) remove the UJ and towelling and the old seal. The old seal was not damaged but the sealing lip had completely worn down (compared with the new one) and was barely making contact with the input shaft.

[There is actually not a lot of pressure behind this seal in normal operation, the real hydraulic pressure is directed to the steering rack pistons during a turn operation, or is simply returned to the reservoir (unless the return port is blocked, as when the seal is being forced out). So I think there was little risk of a major steering failure unless the reservoir ran dry.]

13) clean up the top of the steering box and reinsert the new seal, spring side downwards, grey side upwards. (This requires a special tool, plus some care to avoid inserting the seal too far. You can easily make a suitable tool, see notes below).

14) fit the new circlip, ensuring that it is fully in its slot,

15) reconnect the return hose and tighten fully,

16) bleed the system if required (it has an automatic bleed function so manual bleeding shouldn't be required if you follow the instructions and don't loose too much),

17) run the engine and check for leaks, and then grease and refit a new dust/dirt seal, it clicks in a groove on the input shaft with the lip in a slot on the top of the box,


18) refit the steering column, rubber boots, headlight frame and grille,

19) do a road test to exercise the steering box (carefully, the brakes are hydraulic powered as well as the steering), check for leaks and recheck the reservoir level. Do this several times over a few days.

What you need

1) An input shaft seal kit seal kit. I acquired this kit (part number TAS75/C1) from the local TRW importers, Complete Steering Australia Pty. Ltd, Phone (03) 9369 2659. They were familiar with the Oka steering box and the seal kit was around $80 delivered. This sounds a lot but it contains the seal, dust/dirt cover and new spring clip, plus a couple of other items not needed for this fix, and it's difficult to source from elsewhere.

Input Shaft Seal Kit.

2) 2 hydraulic fittings, a Ryco S56-12 or Pirtek AU-12 male plug, and a Ryco S65-12 or Pirtek AW-12 female cap, or equivalent (about $5 each). Hydraulic pressure is used to force the old seal out and these are for temporarily capping the return outlet on the box to create internal pressure, and plugging the return hose to prevent fluid loss.

Cap and Plug for the blanking off the return outlet and hose.

3) A special tool for inserting the seal. You can buy one ($US36 from the USA plus freight, assuming the J37073 is the correct size, or around $A100 quoted locally), or you can quite easily make something similar, as it's only a stepped cylinder. The TRW manual warns against using a socket to insert the seal since if you go too far it won't seal, and might require removal and disassembly of the steering box to recover it, which is a big job. However you can use a socket if you adapt one to prevent this from happening.

A long socket modified to avoid inserting the seal too deeply.

4) A couple of litres of Automatic Transmission Fluid (Dextron 111 or equivalent) to replenish the reservoir.

Modifying the seal insertion socket

You'll need a fairly deep socket, long enough internally to surround the input shaft plus a bit, and small enough in diameter to just fit inside the seal housing. A long, 1 1/8 inch A/F, or metric equivalent would suit. To that you can fit some clamps to prevent the socket from penetrating too deeply. Only 4.3 mm depth is required. You may notice that the clamps I used are actually some old Oka saddle clamps from drive shaft rear UJ's, which I opened out a bit and bolted across the socket. You could easily make some similar clamps using 3mm steel bar. I did try hose clips but they are not wide enough to sit on the seal housing and are not flush on their lower edges.

About 4.3 mm depth is required, no more.

After removing the circlip from above the old seal, I "calibrated" the modified socket by locating it over the input shaft and nipping up the clamp bolts while it was resting on the old seal. That gives it the correct depth. Make sure the clamps are then securely tightened as you don't want them to slip up during insertion of the seal and overdo things. It's better to leave things a little short than to drive the seal too deep.

Inserting the new seal

Follow the instruction above, or in the TRW documents. They are similar but I've added some practical tips. These photos may also help.

Old seal exposed after removing the circlip (or spiral spring clip in our case).

The return hose and outlet plugged.

Using the socket to insert the new seal.

(The socket was calibrated this way too with the old seal in place)

It was a little bit squeezy wielding the hammer above the inlet shaft (a slightly shorter socket would have been better), but it doesn't need too much force, and it's a good thing anyway if it prevents the seal from going in too far. In my case the seal didn't go in quite level so I had to tap the socket on one edge to level it up. The seal must only be inserted far enough for the circlip to fit fully in its slot.

The circlip located in its slot above the new seal.

After putting the new circlip in, I removed and replaced it a couple of times to ensure that it really was fully in the slot. You don't want the seal popping at the wrong moment and distributing fluid all over the Oka and road, and leaving you without steering or brakes. If the circlip is not quite in its slot, put the socket back on top of it and tap it down gently until it seats properly.

Remove the plug and cap from the return hose and quickly reconnect to the steering box, to reduce fluid loss, and tighten fully.

To aid the bleeding process, and before reconnecting the steering column shaft and lower UJ, I ran the engine several times briefly as per the instructions, checking the reservoir level in between. Ensure there are no more leaks, from the input shaft or return hose, then grease and refit the new dust/dirt cap. If all is OK, then you can fit the lower UJ and steering column shaft.

The seal and dust cap in place, with blue grease under the cap to keep out water.

Replacing the steering shaft

The steering column shaft can be replaced without disturbing the steering wheel housing but needs to be manually compressed and expanded as it's fitted to the splines at each end. It's better to leave all the pinch bolts off until the shaft and lower UJ are in place. Being able to slide the shaft up and down the spines makes fitting it a bit easier. Ensure that the steering wheel is aligned with the front wheels in the straight ahead position before assembly.

The lower UJ back in place with safety locknuts fitted.

I fitted Nyloc nuts plus extra locknuts to the UJ bolts to ensure they never, ever work loose.

When refitting the steering shaft, according to TRW, the UJ's should be in phase to avoid cyclic binding. I never knew I suffered from cyclic binding but apparently it can occur where there are 2 or more UJ's in the steering shaft and they are out of phase.

"Steering column assemblies with more than one universal joint (cardan type) can cause a cyclic binding feel or torque variation at the steering wheel if the u-joints are not in phase with each other".

I presume being "in phase" means that the UJ cross shafts are parallel, like in this photo, but they don't explain. (Note: the urethane bush clamped to the siding shaft is to reduce steering column rattle, which works well and could easily be installed at this point, see this article).

Steering shaft with UJ's in phase, I think.

Replacing the rubber boots and steel framing brackets is easier if they are first slit/cut up the back. You don't then need to slide them over one end of the steering shaft where they get in the way of reconnecting it. The steel clamps should hold them in place but they can be super-glued if you need to, or as I did, hold them together with nylon tie-wraps.

Rubber boots, slit up the back to aid assembly.

(They were cleaned before reinstallation)

I also fitted a leather boot to the the lower UJ to protect it from the worst of the dust and water.

Leather boot to protect the lower UJ.

GARP, The Great Axle Reconstruction Project (Part 2)

Intro

In GARP Part 1, I described the events leading to disassembly and repair of the front axle. GARP Part 2 describes the reassembly process.

Hubs and Spindles

Following on from Part 1 which was initiated by a front end vibration, I have now cleaned up the spindles, removed the diff inner oil seals and checked the bearings for fit on the reground spindles. The shells are a tight fit, or rather, they need accuracy in location or they will jam sideways. Once correctly located the bearings slide and rotate very smoothly. Of course, once the bearings are tightened up the shells shouldn't move or rotate on the spindles anyway.

I removed the rear hub oil seals, using an inside gear puller pressing on a steel bar placed across the hub, but before replacing them, I tried the hubs and bearings on the reground spindles, temporarily reattached to the steering knuckles. This is to ensure they can be correctly assembled without jamming when the hub is offered up to the spindles. Had the inner bearing jammed on the spindle, it would have damaged the new oil seal when the hub was removed.

If the bearings are jamming, smoothing the spindle with some fine emery cloth and careful cleaning with WD40 will help, as will a smear of oil on the bearing surfaces. Older bearings will fit slightly easier than brand new ones.

If the hub and bearings can be successfully located on the spindle without jamming, a new oil seal can be pressed into the rear of the hub, by gently tapping around the edge with a heavy hammer until it's flush with the hub casing. Don't knock dirt from the back of the hub into the bearings.

Oil seal inserted into the rear of the hub.

Diff Carrier Rebuilding

Refer to Section 4 of the Dana 70 Maintenance Manual (available here) and the Carrier section of the Dana 60 Maintenance Manual (available here) for advice on how to do this. The front axle of an Oka is actually a Dana 60 while the rear is a Dana 70, but there are many similarities and the techniques in these manuals are relevant to both types. In fact there's a host of useful documents available from the Dana website here.

After removing the diff centre carrier, I unbolted and removed the ring gear, knocked the roll pin through and removed the cross shaft and differential gears.

Because it's a heavy item and would be seriously damaged if it fell on the concrete floor, I inserted a sturdy cable through the carrier and tied it to a roof beam so that if it slipped out of the vice whilst being worked on, it would swing clear and only hit me, not the hard concrete.

Removing the ring bolts was easier than anticipated since they should have been torqued to 130 ft-lbs (176 Nm) and Loctited too. I left four of the bolts partly in place and tapped them with a hammer to free up the ring gear, which wasn't very tight anyway. I moved the carrier from the vice to the workbench and then removed the last 4 bolts whilst holding the ring away from any hard objects. I didn't want to have to replace that as well, since ring gears only come as matched pairs with the pinion, which would have made it a much more difficult (and expensive) job.

The Ring Gear being removed.

Leave 4 bolts loosely in place and tap the heads to release the ring.

The bearing cups came away when removing the diff centre, so I put old socks over each of the bearings to protect them while this work was being done.

I tapped out the roll pin using a length of 5mm steel rod, and the cross shaft then slid out of the carrier.

Removing the differential gears looked difficult since they remained meshed together, but by turning a side gear, the spider gears simply walked themselves around to the opening in the diff and fell out. All 4 gears are seated on thrust washers which might be stuck to the carrier by oily suction.

I smoothed the rusted and pitted surfaces of the ring gear with fine emery paper and WD40 and cleaned them off with Brake Cleaner fluid.

The broken gear wheel will end up in my Museum of Broken Car Parts which is becoming quite extensive.

The diff in pieces ready for reassembly.

The Differential Gear Set.

A close up of the offending tooth.

Diff Oil Seals

Removal of the Inner Seals

To remove the inner diff oil seals I built a pusher rod made of a metre of 12mm tapped rod with a large steel washer, just the diameter of the rear guide section of the seal, bolted to the other end. A few whacks with a heavy hammer and the seals popped out into the diff chamber. Other people have used a large socket and several extension bars to achieve the same result, but I didn't have the right size socket (or sufficient extension bars). The bar needs to be at least 1 metre long to remove the LHS seal.
This bar, with a sock tied over the washer, also makes a useful tool for cleaning out the oily/muddy sludge from the axle tubes.

The pusher for removing the inner seals and cleaning out the axle tubes. 

Installing the Inner Seals

To insert the seals I used a modified 40 mm high pressure water fitting, which just fits inside the seal body, to avoid damaging the plastic parts of the seal with a hammer. The fitting will need to be cut down to about 50 mm long to allow a hammer to be swung inside the diff housing. I drilled and fitted a long bolt to the side of the plastic fitting as a handle, to keep my thumbs well clear of the hammer. A suitable socket might also work. Alternatively a pusher tool could be made up as described in the Dana 60 manual. Any rust or corrosion around the seal location should first be removed and the surfaces smoothed down.

The old seals had silicon gasket sealant smeared around their outer surfaces before insertion, presumably to keep water away from the metal surfaces and prevent premature rusting. Seems like a good idea, as does greasing the seals and guide inner surfaces to help the splined drive shafts find their location.

However, sealant on the seal casing also makes them slippery and more difficult to keep centred as they are inserted. It takes a quite a lot of effort in a confined space to insert the seals straight, since they are a tight fit, and I had to remove and reinsert one of them a couple of times to avoid fitting it crookedly. A pusher tool would certainly be more effective.

Mind the pinion gear, bearing seats and thumbs as you are wielding the hammer, damage to those would be expensive and/or painful.

Clean out all the resulting muck from the diff housing.

A pusher for removing the inner seals and cleaning out the axle tubes

can be made by cutting down a 40 mm high pressure water fitting,

which fits neatly inside the body of the seal, to about 50 mm long.

Reassembling the Diff Carrier 

Before reassembling the diff centre, ensure that the ring bolts and tapped holes in the ring gear are thoroughly cleaned and free of old Loctite.

Before the ring is refitted, the new gear set must be installed, with their thrust washers, and the cross shaft and roll pin inserted. Oil all the parts well before assembly and check for smooth rotation.

Installing the Differential Gears

You'll need about 15 fingers to hold the 4 gears and their thrust washers in the right place but it's not too difficult. Insert the side gears first on their washers, with the carrier horizontal so they can't fall out. Then insert both spider gears exactly 180º apart from either side of the carrier and walk them into the carrier case by turning both side gears in the same direction. If they are not exactly 180º apart on the side gears the cross shaft holes won't line up. I found it easier to slide the saucer shaped thrust washers in behind the spider gears after the gears were in place.

Gears reinstalled in the carrier.

Once all the gears are in place, centre the the spider gear washers with a finger and insert the cross shaft with the roll pin holes roughly in line. Use a thin bar to turn the cross shaft until the roll pin holes line up and drive in the roll pin. The differential gears are now complete, assuming they all turn smoothly.

Driving the Roll Pin home to complete the assembly.

Installing the Ring GearThe ring gear should be replaced in its original orientation (not sure why, it doesn't seem to be a balanced item, but that's what the manual says) and this can be determined from the imprint markings on the carrier made by the ring. There is a cut out on one side of the ring, presumably for oil flow, which will show up as a shadow on the carrier. I also took photos of the stamped markings to confirm it's location.

The manual also suggests replacing the 12 ring gear bolts, but they are very high tensile bolts (SAE Grade 8, equivalent to metric class 10.9) and if they are in good condition and not stretched or worn, the originals could be reused. On a rear diff, which is subject to a far higher and continuous load, I would certainly replace the bolts.

[BTW, if you are excited by such things, there is a very good Australian document on bolts (and fasteners in general) available for download from the James Glen Company here, or view an on-line version here].

The ring bolts need to be tightened alternately to 130 ft-lbs (176 Nm) and Loctited. A tight fitting socket is required (hex, not multi-point is preferred to avoid rounding the corners) and the carrier needs to be securely held in a large vice, preferably tied to something substantial to catch it if it breaks loose. Vice jaws have been known to snap off. Protect the exposed bearings while doing this.

My torque wrench only goes up to 110 ft-lbs so I tightened the bolts alternately to 110 ft-lbs and then used a longer bar to turn them all a fraction of a turn more, about 25º to 30º (1/12th of a turn max.). I reasoned that this would increase the torque to around 130 ft-lbs. Don't forget the Loctite and ensure you haven't missed out tightening any bolts, 12 is a lot to remember.

Reinstalling the Diff Carrier

Fully fitted with gears, the carrier is a bit of a handful to manage under the vehicle. It has to be manoeuvred around the tie rod, the bearing cups have to be fitted and held in place and the whole assembly inserted straight and level into the housing so that the pinion engages with the ring gear and the bearing cups locate correctly in their slots. And it's heavy and makes your arms ache.

The bearing cups had previously been rotating in their housing and caused a burn mark so I applied some Loctite 641 (bearing retaining compound) to the housing and bearing caps to stop them rotating.

The differential installed in the carrier.

It took me a couple of goes before I could locate the carrier properly, but I had the bolts and bearing caps ready to go so that when finally it slipped into place I could whip in a bolt to hold it there before it all fell out again. Had the diff carrier been a press fit requiring a diff spreader to remove it, I doubt that it could have been replaced in situ and the axle would have had to be removed first.

Once I had recovered my strength and confirmed that the gears all rotated correctly, I Loctited the bearing cap bolts and torqued them up to 80 ft-lbs. The bearing caps should be replaced in the same orientation as previously. They have stamped markings on to aid identification.

Fitting the Drive Shafts

Once the diff is in and working correctly (although I don't see how it couldn't work as it's a very simple but clever mechanism), the drive shafts can be installed.

I had already cleaned them up, checked the UJ's and replaced the oil seals. I was surprised to find the short shaft UJ had a grease nipple, which worked. It must have been hidden under years of dirt and sludge and in 5 years I had never noticed it. Presumably this UJ, or maybe the complete shaft, had been replaced at some stage as the inner splines were also much less worn than the long shaft, which had no grease nipple. Fortunately there was little play in either UJ.

When reinstalling the drive shafts I wanted to avoid the splined end from collecting dirt, as it was pushed along the axle tube, and injecting it into the diff housing. So I placed a thin plastic strip in the axle tube and slid the drive shaft along that and straight into the diff. The plastic strip was actually the cap from a length of Clipsal rectangular electrical conduit and acted like a thin "V" shape for the splined shaft to slide along. When the shaft had entered the diff housing but not fully engaged with the side gear, I pulled the plastic strip out of the axle tube and pushed the drive shaft home, all nice and clean.

Using a length of plastic strip to keep the drive shaft out of the dirt.

The oil seal has also been replaced.

Refitting the Spindle 

Before refitting the spindles, I levered out the old oil seals (which had broken in 2 anyway), flushed out and re-greased the needle bearings and tapped new oil seals into the back of the spindles.


Clean and grease the rear of the spindles around the needle bearing seal since the drive shaft oil seal engages that surface.

Needle bearings greased and new oil seal fitted into spindle.

Strangely, I couldn't recall the order in which the spindle, brake calliper plate and stone guard came off, so I thought "simple, I'll look it up in the manual".

Wrong. There are pictures of the axle, spindle and hub arrangements and pictures of the brake rotor and calliper, but none showing both. Eventually I deduced that the spindle is attached direct to the steering knuckle with the brake calliper plate on next and the stone guard on last. It didn't look right, due to the cranked angle of the calliper plate and stone guard, but it was logical when I thought about it.

Loctite the spindle fixing nuts and tighten them to 65 ft-lbs. Once the hub is in place you can't reach them anymore.

Refitting the Spindle, drivers side.

Grease the rear oil seal bearing surface and clean out the spindle nut threads. 

When fitting the hub to the spindle, have the greased up outer bearing and the hex spindle nut ready to go. Otherwise, when you fit the hub with only the rear bearing in place the hub might slip down the spindle when you let go.

I was tempted to put bearing retaining compound on the bearing cup surfaces to prevent the original problem of the bearing cups rotating on the spindles, but there is so much grease around that I doubt that the retaining compound could do it's job effectively. With rebuilt and reground spindles it shouldn't be necessary anyway.

The spindle nuts should be tightened to 50 ft-lbs, spun a few times to seat the bearings and circulate the grease and then backed off about 45º before fitting the lock washer and outer lock nut. Pre-loading is essential for tapered roller bearings so they share the load equally. If there is any free movement, they are too loose. On the road I check the temperature of the hubs frequently to ensure they are not getting too hot. Warm is OK due to the brake heat, but if one is appreciably hotter than the others, something is wrong.

[There are some very useful tech notes on bearing problems and installation at the Timken site here and here].

Fitting the lock washers can be a tricky task. Bend 2 tabs in towards the bearing, being careful not to go too far or you can damage the bearing cage. I used a rod formed from the tapered end cut off a tent peg to do this. Bending 2 tabs outwards on to the lock nut is even more difficult. I made a small tool using another tent pen with a sharp bend on one end (more than 90º so it won't slip off) and threaded the other end. Using a breaker bar with a hole it it, I slid the tool in behind the tabs and levered against a nut fitted on the threaded end. Once the tab has bent slightly, I used a square shank screwdriver to lever them flat by twisting it with a wrench on the shank.

[In the US, there are more sophisticated (but expensive) locking devices described here and here].

Epilogue

The rest of the rebuilding process (free wheeling hubs, tie rod ends, steering damper, brakes, wheels, diff cover/oil etc.) should be fairly straight forward, but as with any major project, check if there are any bits left over and check that everything is reconnected, tightened, greased or refilled.

On it's first test run, there was no evidence of the original vibration which kicked off the whole axle reconstruction program in the first place, and the steering seemed a lot smoother, although there's no logical reason for that other than the greased joints. I ran the Oka in 4wd for a while, but with the hubs unlocked, to allow oil to circulate through the diff components before any load is applied to it.

This has been quite a long and complex rebuilding process and ironically, there will be almost nothing to show for it at the end, except peace of mind.

However, it is not difficult or mechanically challenging or even very expensive, there's just a lot of it.