Starter Solenoid/Armature Failure Analysis

Starter Motor Failure

Our starter motor failed in mysterious circumstances at Eucla, half way across the Nullarbor Plain. We'd stopped to use the facilities at the Eucla Roadhouse and afterwards, the starter motor refused to function.

The solenoid on the starter motor had been giving intermittent trouble for a couple of years and usually tapping the start relay connection was enough to get it going, but not this time. I replaced the solenoid but the motor was still faulty so we eventually assembled a working one out of spare parts and found that a replacement armature was also required to get it going.

Further analysis on the faulty components was obviously required after we arrived home. This is it.

Solenoid Failure

In Eucla I took the solenoid off and checked it electrically. Not surprisingly one of the windings had failed internally.

Since these are not repairable items (at least, not without a lot of effort and desperation) we ordered a new one which took a couple of days to be delivered from Perth. In the event that didn't fix the starter problem and we had to wait until we could bump start the Oka and travel on to Coolgardie, without switching the engine off, where I could fix or replace the motor.

The second, concurrent, problem was a faulty armature, which turned out to be a winding fault, rather than excess commutator wear (which would have been simple to fix). Why and how we could have 2 problems which occurred at the same time is still a mystery, unless the solenoid was in one of its in-between failure periods and it was actually the armature which failed first. I guess we'll never know but it did delay us for a few days, luckily right outside the Eucla Motel.

Opening up the Solenoid

The starter solenoid is assembled into a steel cylinder, the top edge of which is peened over during the manufacturing process to hold the contactor plate in place, so it can't be easily be disassembled.

Electrical operation of a starter solenoid is explained in this useful article.

I first unsoldered the winding wires from the terminal posts (there are 2 wires on one terminal) using a solder sucker and desoldering braid to remove the solder. The thinner wire came completely out indicating a broken or fused wire in the hold-in winding. Then I cut through the skin of the cylinder near the contactor using a hacksaw and removed the internal components.

Where I cut the solenoid cylinder The contactor removed after cutting though the cylinder The windings are wound around a plastic former on a steel base plate which is held in place by a large circlip. The fused hold-in winding and circlip holding the coil base plate in After removing the circlip and sliding out the coil assembly, it was immediately obvious that there had been a burning event and both windings were burnt black at the terminal end. Although the hold-in coil had failed, it was unclear whether the thicker pull-in winding had overheated, causing the thinner hold-in winding to fail, or vice versa. Windings removed The burnt windings. The thinner hold-in winding is wound over the top of the thicker pull-in winding, separated by paper insulation. Solenoid Repair Possibilities

The solenoid is a fairly simple electrical device and if necessary it could be rewound and reassembled by cutting out the burnt sections of wire (the insulating enamel may have been damaged by heat causing further short-circuits) and rewinding them. The windings both have around 100 turns on them so a few turns missing would not affect operation appreciably. The cut off cylinder could be repaired using a hose clip, tie wraps or similar to hold the contactor plate in place.

Pull-in winding after removal of the hold-in winding

Although the solenoid could be repaired if the situation was really desperate enough, it's probably a better choice to carry a spare at around $100 and save all the potential angst.

Contents of the solenoid "To reassemble, simply reverse the disassembly process"

Causes of Failure

There was no obvious mechanical or electrical reason for the winding to fail, but possible causes are:

• Prolonged engagement of the starter motor, allowing the windings to heat up to the point where the insulation breaks down, causing a partial short circuit and leading to eventual winding failure, or
• Heat from the exhaust system which runs nearby, aggravating the internal self heating of the solenoid windings and leading to the same result. This is most likely to happen when restarting an already hot engine (which coincidentally is exactly what happened to us in Eucla), or
• Shit just happens when you least expect it.

The solenoid on our Oka is very close to the exhaust

Using Iskra starters (and possibly other makes), there are 2 frame types with different locations for the starter solenoid:

• on the side of the motor (which is close to the exhaust pipe on our Oka), or
• below the motor where it's more exposed to impact damage (but no more so than the engine sump would be).

There is the merest possibility of the front drive shaft or its capture hoop touching the solenoid in the lower position at maximum axle articulation, but that seems most unlikely to happen in practice as the bump stops/airbags would have to completely fail to do their job.

Solenoid located on the side of the motor, like ours, Iskra IM527 Solenoid in the lower, but more exposed location, Iskra IM315 The only difference between the motor types is the position of the solenoid and therefore the battery cable runs. A solenoid in the lower position on an Oka My preference now is for the lower location since impact damage would be rare and obvious, rather than the side location (which is where ours is currently) where the solenoid is exposed to continuous exhaust heat, so I shall be changing mine for the lower type and fortunately I have acquired a spare frame of this type. For starters with the solenoid near the exhaust, I recommend fitting a heat shield of shiny aluminium, or even reflective tape, between them to reduce the effects of radiant heat.

Armature Problem

Well I've now done some analysis of the faulty armature.

I started by buffing up the commutator to ensure that the brushes would seat properly and eliminate that as a problem. I didn't have a lathe big enough to hold the armature so I made a simple stand by clamping the bearings on each end in small vices clamped to the workbench. I then turned the armature by hand and used a flat file to dress the commutator. [I did try using a cordless drill and belt to turn the armature but too many hands were needed to hold it steady and it only took about 10 minutes anyway].

Rudimentary lathe assembled to dress the commutator

Once the armature was smooth and flat, I rebuilt the motor and tested it on a car battery using jumper leads.

The motor still didn't turn but a whiff of smoke indicated where the problem was: 2 adjacent segments are presumably shorted internally and a burn mark was evident on the end of the commutator where the smoke appeared.

The burn mark where the smoke appeared from.

To confirm that this was not caused by internal short circuits in the area of the brush plate, field coil connections and/or fixing bolts, I removed the end cover and held the motor in a vice while applying voltage.

The motor still didn't turn but it put up quite a light show to confirm there is indeed an internal problem with the armature, irrespective of its rotational position.

A light show but no movement, and I was wearing eye protection.

Conclusion

So the armature would seem to be completely cactus and probably not worth repairing. But it also confirms that our problem in Eucla was indeed caused by 2 concurrent problems, the failed solenoid and an armature fault, although I now suspect that the armature fault was the primary show stopper.

The fixed field coils seem to be very robust so should be more reliable than rotating/sparking parts:

• They don't move,
• They're made of thick, solid copper bars,
• I have a spare set.

Brushes can be replaced and I have a spare set, plus brush plate.

Solenoids can be replaced (I now have a spare), bypassed or even fixed on the side of the road but not the armature.

So the question now is whether to acquire a new or s/h (spare) armature or a whole new (spare) starter motor or get this one repaired.

Or do nothing and hope the existing one will last for ever.

Minimum Electrics to Start the Engine (Injector Pump Solenoid Fix)

On an Oka, there is only one critical electrical item which keeps the engine running or not, and that's the fuel cut off solenoid at the back of the injector pump. (Bosch call it the ELAB, electronic shut off device. This Bosch Instruction Manual is a very valuable resource on the VE pump).

As long as you can start the engine (maybe by bump starting it if you have no battery power or the starter has failed), that solenoid wire with 12v applied is the only electrical thing needed to keep it running and a even small 6v lantern battery would probably do.

Minimum Electrics to Start and Keep the Engine Running

Even if all dashboard "ignition" functions are disabled, connecting up the fuel cut off solenoid to 12v and hot wiring the starter motor to the battery (or batteries) should start the engine (in neutral of course with the park brake on since you'll be under the vehicle). The key is still required to unlock the steering though.

Connect the Start Relay connection on the starter relay body (a small terminal between 2 large ones) to the battery +ve to engage the starter gear (only a thin wire is required), and remove it when the engine starts. (One of the large terminals will be a battery +ve connection so only a short wire is needed, even a screwdriver would work).

If there's only a click, or nothing at all, the battery wiring is suspect so you may also need to use a thick jumper lead to connect the battery +ve to the main starter motor terminal (which is probably on the starter relay body, not the actual starter motor, follow the (red) wiring from the battery), but it should already be connected. The lead on our starter motor body is actually a (black) ground connection.

Also check that the battery -ve is effectively connected to the chassis or frame of the starter motor using the other jumper lead.

Disconnecting the fuel cut off lead will stop the engine (or it can be stalled in a high gear by gently letting out the clutch with the brakes on).

If the engine rotates but doesn't start, it's a fuel problem (or less likely, a major mechanical fault) and that could be the solenoid. But it could also be the lift pump, or you could be out of fuel, or have air or a blockage in the system so check out these and all other possibilities before accusing the solenoid.

What if the starter fails?

Another obscure fault we have had is an intermittent winding connection inside the starter solenoid on top of the starter motor body. This can prevent starting on an otherwise healthy vehicle and are not repairable items so a spare would be a wise investment (about $100). Pity we didn't have one when ours failed, we had to have one shipped from Perth to Eucla.

The solenoid with the dodgy connection, after I reflowed the solder to try and fix it. The contactor inside can still be used to connect the starter motor by pressing the plunger on the other end

A possible bush repair in this case is to:

1. remove the starter solenoid (three long philips head screws on ours and you'll probably need to remove the starter from the engine first),
2. use a mechanical method (eg a rod with a slotted head tie-wrapped to the motor body) to pull the gear lever inside the housing backwards away from the housing (to engage the starter gear) and
3. ensure the gears are in neutral and connect the starter motor connection to the battery +ve manually, using the internal solenoid contactor (and pressing in the internal plunger to bridge the contacts), a high current (300A+) relay (like the one for paralleling dual batteries) or or even a thick jumper lead. Connecting  batteries in parallel will help to drive the starter motor.

Jumper lead connections may spark a lot and weld themselves together so use a very thick steel bar to absorb the heat and wear glasses (using the solenoid contactor or relay captures any sparking), but the motor should now turn over and start the engine.

Quickly remove the connection or release the plunger as soon as it starts, and push the rod so the solenoid gear lever moves forward into the housing, disengaging the starter gear. The rod can be tie-wrapped to the motor body so that the gear can't accidentally re-engage.

The gear rod pulled forward to engage the drive

You would need to do this each time you need to start the engine so it's only an emergency fix, so leave the engine running during all short term stops and think about restarting options before switching it off. Doing this is a busy car park or on the road side would be potentially dangerous or frustrating.

If all else fails, the Oka can be bumped started quite easily. With a couple of people pushing, the Oka will roll quite well on a hard surface and 5 tonnes of Oka has sufficient energy to turn over the engine, even when moving slowly.

Checking the Fuel Cut Off Solenoid (not to be confused with the Starter Motor Solenoid)

I have rarely read or heard of a failed fuel cut off solenoid, whereas broken wires and terminals are commonplace, so check that it really is the solenoid first, before removing it. It should have a low resistance to ground, a few ohms (probably around 10 to 20 Ω, check it by connecting a 5W globe in series to +12v, it should glow if the solenoid coil is OK). If you can hear it click when voltage is applied it's probably OK too.

 

What if the Solenoid has Failed?

If the cut off solenoid itself really has failed (other than a broken terminal screw, and you could tape a wire to it to maintain contact), the engine can't start. I did think that removing the solenoid and using a magnetic pick up wand to engage the valve may work. However the solenoid valve also seals the rear injector port so removing it would allow fuel to leak out, probably under pressure, so that trick won't work. (See this photo of a disassembled solenoid valve and its location). In this case replacement or modification (see below) of the solenoid is the only answer. This is now on my list of "Things To Do If Desperate".

Fixing the Solenoid

One good suggestion I have seen (thanks to RedZerOne) is a simple modification to a failed solenoid to get the engine going:

"When mine went out two years ago, I gutted it rather than replace it. To do this, remove the solenoid from the VE pump [edit: 15/16 inch spanner] and remove the plunger and the spring from inside the solenoid. Double check in the pump and solenoid that there's no debris and reinstall the solenoid. This will allow the engine to have fuel constantly. It'll operate the same as if you had a working solenoid, the only difference is that in order to shut off the engine, you'll have to manually stall it out. I've been doing this for two years now with no problem."

Remove the spring and plunger and reinstall the solenoid Photo courtesy http://bricofoy.free.fr/phpwebgallery/

Note, no electrics to the pump are required after this mod and the fuel will be permanently on, which doesn't matter except that the engine won't stop and would have to be stalled. However getting access to the solenoid might require removal or loosening of the top section of the pump, but if you're desperate enough anything goes.

[In fact if you can bump start the Oka after parking on an incline (I'm not sure how easy this is with a diesel, try 2nd or 3rd gear), you wouldn't even need any batteries after this mod to the solenoid. Caution, if you ever try this without batteries, disconnect the alternator first to avoid generating high voltages after the engine starts which could damage any electrical equipment. The batteries normally constrain the voltage to around 14v, even dead ones, but an unloaded alternator can generate up to 100v at very high power and can even be used as a welding supply].

This the solenoid location on our injector pump.

It looks inaccessible, but with a 15/16th spanner or shifter it should be possible to remove it.

The solenoid is on the right, with the top of the pump removed.

It shouldn't be necessary to go this far, I was replacing the throttle shaft seal when this photo was taken.

Electrical/Electronic Mods to our Oka

Being an electronics engineer it was inevitable that I would make and installed lots of electrical/electronic modifications and additions to our Oka.

None of these mods affect the basic functionality of the Oka, in fact there is only one essential electrical item which keeps the engine running or not, which is the fuel cut off solenoid on the injector pump.

As long as you can start the engine, the solenoid wire with 12v applied is the only electrical thing needed to keep it running. See this post for the minimum electrics to start and keep the engine running.

Electrical Mods to our Oka (** indicates my own design/construction)

Mods which relate to Driving

• Smart alternator regulator for our 120A alternator (Sterling AR12VD)
• Triple batteries with automatic charge connection and manual paralleling switches**
  • Supercharge Gold MF95D31R (760 CCA) starter battery
  • 2 x Supercharge MRV70 (105 AH, 760 CCA) Allrounder (Starting and Deep Cycle) house batteries
• Solar panels (200W, 10 x 20W) and multiple battery charge controller**
• Charge monitoring display system (current and voltage)*
• Start Lock Out system**
  • Prevents the engine from being started until an enable button is pressed, after the ignition is turned on
  • Fitted with an emergency engine stop button
• Reversing and forward facing (for seeing over crests) cameras and 9 inch LCD display
• Wiper delay system**
  • 6 delay periods
  • 1 or 2 wipes per cycle
• Dashboard electronics**
  • Voltage and charge current meters switchable to each battery (LCD and LED)
  • GPS PSU
  • Turbo Timer
  • Headlight/Step/Vent/Pump "Left On" reminder system
  • Laptop PSU for moving map system**
• Remote central locking doors**
  • Fitted to all 3 doors, with interlocks so that any internal door handle can lock and unlock all doors**
• Electric windows on both front doors**
• Remote switching of fridge dc**
  • Allows fridge to be switched off from cabin when stopped (eg for fuel), to reduce battery load. Normally the fridge runs from 240v ac via the inverter while travelling as it's more efficient than dc, less cable losses. Solar panels provide power when the alternator is not charging
• Automatic inhibit of Water Pumps**
  • Inhibits pumps when the ignition is ON, to prevent accidental pumping out of water if a pipe leaks or breaks while travelling
• Diesel Transfer Pump to transfer fuel from rear to side tank

Mods which relate to the Motorhome

• System switch functions for all rear electrical equipment**
  • Pumps, Lights, Fans
• Water Level Meters for both main water tanks**
• Fridge/freezer monitor and alarm system**
  • Display of fridge and freezer temps
  • Over temp and flame failure alarms
  • Indication of energy source (ac, dc or gas)
    •  Note: Fridge is normally powered from ac inverter while travelling
• Fridge Fan to circulate cold air, stops when door is opened**
• Fridge LED Lights which operate when door is opened**
• Window Fans to cool us at night (speed controlled from quiet breeze to gale force)**
• 300W Sine Wave Inverter (Jaycar) with RCD
• Soldering Iron, 24v 60W, temperature controlled, runs from dc-dc converter**
• Drill battery charger, 24v, microcomputer controlled
  • Runs from same dc-dc converter as soldering iron
• Computer systems
  • GPS moving map system based on MacBook, USB GPS and Oziexplorer running under VirtualBox and XP
  • 17 inch LCD display mounted on engine cover
  • NextG Phone/Modem,( plugs into MacBook), with external whip and Yagi antennae
  • 2 x 40W channel HiFi system switchable from radio to computer**
• Smoke Alarm inhibitor**
  • Prevents activation while cooking. Manual reset or automatic reset after 40 minutes
• NiCd/NiMH Battery Charger (up to 10 batteries at once)
• Rechargeable Dolphin LED Torch using 8 1/2 W LED's and 6v SLA battery**
• Dustbuster converted to run from 12v (internal 12v to 6v switching converter)**
• HF Radio, (Codan 7727 with VKS737 frequencies)
  • Modified to receive ABC and BBC shortwave broadcasts
  • Allows transmit/receive on the 40 meter (7 MHz) amateur band (call sign VK5MDR)**
  • Frequencies can be selected via an external VFO**
  • Allows broader range of emergency frequencies
  • Jenal SC2 microphone fitted to allow direct RFDS connection via Selcall though VKS bases**
  • Tapped whip and 9m Super Rod antennae
• SW Battery Radio
• LED Lights**
  • External LED camping lights
  • Internal LED lights
  • Automatic porch/step lights (comes on at dusk when door is opened)
• Fridge dc low voltage cut off**
• Roof Vent fan speed control**
• Evaporative air conditioning controls**
  • Controls small evaporative a/c for use when the engine is off
  • Provides automatic shots of water to keep the evaporator pads damp instead of a continuous supply, to save water. Uses a timer to control a solenoid valve from the pressurised water supply

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.