W108 rear axle hydro-pneumatic compensator: How do I know if it is good or bad?

[GGR]

Hi all,

The other day I took a rear axle out of a W108 4.5. Before taking it out the car's height was normal, and once taken out the compensator doesn't seem to leak like some I have seen which were very oily/graesy. I have now taken the compensator out of the axle and cleaned it. It looks more recent than the rest of the axle. How do I know if a compensatior is good for sure, is there anything that can be checked to know its condition? I attach some pictures:

[Chas H]

If the rear height of the donor car appeared normal, the compensator is very likely good.
when the compensator fails the rear end will sag and a bunch of negative camber will be apparent.
There may be a mfg date on the compensator that could be later than the production date of the car if the compensator were changed.

[JMela]

Slightly OT, but was it difficult to pull the 4.5's rear axle? I'm planning on doing the same in a few weeks.

With regards to the compensator, you might figure the best bet is to have it rebuilt. Figure after 35 or so years the rubber and plastic bits are degrading.

[SoCalw111w123]

WAY Off Topic: I actually enjoy how "Low" my coupe sits with its faulty compensator!

[GGR]

JMela, I got help from someone and it took us a full morning to take the axle out. But we are not professionals. You will need two jack stands and a jack that you can put under the trail arms when you remove them with the suspension springs. The normal W108 MB jack won't do, unless you instead put something under the trail arms to retain them when they are unbolted and lift the car with the MB jack. Start by undoing all what is connected to the axle: brake lines, emergency brake cables, drive shaft, shock absorbers. Then undo the front of the trail arms making sure they are retained by something, otherwise the suspension spring will push them down violently, and the car will also fall down if it is not held by a jack or a stand. In our case, things went smoothly, no spring jumping all over the place. But it can be dangerous if miscalculated. Then I undid the central bolt in the trunk. I had to hammer the central arm down (with the bolt back into it half way) as the arm had seized in the mount. And the axle was out. While manovering the axle, make sure the right part does not come down all the way violently as this can damage the central casing under the rubber. You won't see it without taking the rubber out but it can brake under there.

[Rauchen]

I've notices that my 108 sits just a little lower in the back compared to the front. The camber seems fine though. I'm assuming you mean the camber of the rear tires. The difference is maybe a inch or two. is this possibly the compensator? Also are they adjustable in any way? Meaning, can I raise the rear at all with an adjustment to the compensator?

[GGR]

In normal operating conditions, the camber of the rear wheels should be 0°, the wheels should be perfectly vertical. The front of the car should be lower than the back, by one inch or so. This is measured at the bottom of the rocker pannel, in front of the front jack stand, and in the back of the rear jack stand. Don't trust your visual impression as the different design of the front and rear fenders make the rear wheels look more "upwards".

I had a look again at my compensator, and it seems there is an adjustment on the right side: by undoing a bit the ball joint this may affect the camber. On my compensator it is completely tightened though. And this is only a guess, I'm not sure at all of it. If you want to try it, you'd better secure the car on jack stands and check how much thread there is in there. You don't want the car to fall on you while you're under it in case that ball joint gets loose!

This second look to my compensator confirmed it was definitely newer compared with the rest, there is a very clear difference with the paint of the right bracket still on the compensator. I couldn't find any mfg date, but there is a green mark on the body of the compensator. Does anyone know what it means?

[Rauchen]

I did some reading last night on the hydro pneumatic strut. It appears they are not adjustable. But, apparently, under the rubber boot there are two filler plugs. This is the term used by Haynes. Possibly the fluid can be replenished, if need be, but I'm not sure. The nut you spoke of on the one side is a self tightning lock nut. This just is an anchor for that side. I did check my camber and it is off. The top of the rear tires lean in slightly. I confirmed this by putting a level against the tire. I jacked up the rear, off the ground then put it back down again. This fixed the problem till I drove the car this morning lol.
I think the best fix for these is just to replace with a spring. From the factory some of these cars had the spring, others had the hydropneumatic strut. The only difference is a slightly smoother ride with the strut. But the spring is going to be a lot cheaper to replace.

[sjefke]

I have a spring in my 111 3.5 coupe instead of the hydro-pneumatic compensator. Car sits up a bit in the rear (looks slightly hotrod-ish), but maintenance is easy (none)

Bert