Rear Height Problem

[kcleong18]

Hi guys,
While checking the problem of different rear heights between offside and nearside wheels I noticed the nearside rear arm is drops lower than the other side. This is with both wheels up and system depressurised. What would be the cause of this? Rear arms does not seem to have any play so can I rule out rear arm bearings causing this?

I have also loosen the screws securing one side of the anti roll bar to the arm but this seems not to have any effect. Am I looking at a broken rear cylinder ? Car still rise and sink 'normally'.How easy is it to swap rear cylinders? I have already swap the rear spheres.
Sorry to post so many questions at once but would like to know some possible answers to avoid unnecessary dismantling. I have been reading this forum for a while and it is great info for my 91 XM SEI 2.0 petrol. Thanks everybody.

[steelcityuk]

As a quick guess how about a missing bump stop (low side) or a binding brake (high side).

Can't even find the bump stops on the xm where as the Xantias are obvious.

Steve.

[DerekW]

Hi Kcleong18,

It's unlikely to be a faulty suspension cylinder as these are unloaded when the wheels are unloaded.

A missing bump stop wouldn't affect the ride height and I wonder if you have an anti-roll bar with a permanent twist in it? You say you undid the anti-roll bar bolts on one side; if it was the side with the low hanging wheel then that would have no effect because the arm would already be on its bump stop. Try undoing the high side but put a jack under it first as, if I'm right, the wheel will drop.

Derek

[noz]

Hi kcleong18,

The only thing I can think of is that the electrovalve has one of its ports blocked. When the height corrector is signalled to let the car down the fluid in the cylinders leaks out through the electrovalve and then through the height corrector back to the tank. If the port in the electrovalve linked to the lowest wheel is blocked then pressure will remain in that side.

To be absolutely sure you have no pressure in either cylinder you would have to either disconnect the big pipes to each cylinder or remove the spheres. Be careful though if you try this because there may be residual pressure left in the strut.

Hope this gives you food for thought.

cheers

noz

[onthecut]

Hi Kcleong,

Is it possible you have a damaged or incorrect pushrod on one side ?

Mike.

[kcleong18]

Hi guys,
Thanks for your replies. Will try to digest thems before deciding what to do next.

Steve,
Bump stops are present and reveal themselves when you remove the wheel liners.I consider ride height to be normal when the arm stop is exactly halfway between them.This is how I found out that the nearside wheel ride height is incorrect because the stop is nearer the top bump stop.
Brakes are slightly binding and make noises when wheels are turned but no real pressure here preventing the arms dropping.

Derek,
I agree with you as I am quite sure the arms are unloaded by the cylinders.
Not the same thing I can say for the antiroll bar.Although I undid the screws I have not actually removed them.
Your comments on the twisted anti roll bar does strike me as possible although I do not understand the effect it has on individual wheel ride height.By the way part of the roll bar seems to be rubbing / very near some chassis fixing.

Noz ,
The wheel that drops lower is also the one with the wrong ride height (higher by about 2 cm). If both rear cylinders can be wriggled about with the system depressurized and static can I discount any blockages?

Mike,
I have tried feeling the pushrods through the rubber gaiter but results seems inconclusive. Maybe I can try swapping / removing both rear cylinders this weekend if I am assured of no complications.I don't seem to be able to find nice photos of those rear cylinders on the web and the push rod locking pins looks difficult putting back.Is it possible to remove the whole as a unit together with the rubber gaiter complete?

Best wishes everyone and have a nice weekend!

[onthecut]

Hi Kcleong.

Those I've done, the key issue has been undoing the main feed pipe, either because it has corroded into the thread (steel tube nut, ally cylinder, always a bad idea !) or because it is rusted onto the pipe itself, with the danger of tearing or twisting the pipe. It's well worth preparing the area with some penetrating fluid in advance. Also, having made sure the car is safe and well supported, always make the initial turn of the nut with the system under pressure, otherwise the whole cylinder will twist, deforming the pipe. Same goes for the initial undoing turn on the sphere. Once they are 'cracked', depressurise. If the pipe tube nut is a real sod, I have also used heat, carefully, as the different rates of expansion should ease the breaking of the thread corrosion.
I've been lucky with mine in that the rod retaining pin has always come out OK, but I know from other posts on the forum, they can be awkward. If you go ahead with the strip down, it is a good time to check (and replace if necessary) the rear arm bearings, as the removal of the hydraulics is a big part of that process, as well. Good luck.

Mike.

[Peter.N.]

If you put the suspension on maximum height with the wheels off the ground, presumably both wheels are at the same height as they should be against the bump stops - if not you have mechanical trouble of some sort. If you let the suspension down and check the heights,and one side is now higher, I would suspect, as has been suggested, the the anti roll bar has a twist in it, although how, I dont know. I would have thought the effect would be the same at the lowest height, assuming the weight of the car was on the wheels. This seems strange as I cant understand how even shot radius arm bearings would have this effect. Just a thought, I suppose your rear tyres are not different sizes?

Peter.N.

[Assich]

Just because you can't feel any play in the arms doesn't mean the bearings haven't gone. The bearings went so badly on the first XM I had that the tyre was rubbing against the "boot" wall wheel arch yet there was no play. The bearings had selfdestructed in such a way as to take up any play. The arm still went up and down.

[techmanagain]

You can only check for rear suspension arm bearing wear if the hydraulic system is depressurised completely by opening the pressure releif valve on the pressure regulator below the front (main) accumulator sphere. It is not so much up and down movement you have to check, as ANY slackness when there is no pressure in the system.

[noz]

Hi KCloeng,

OK, if you can rattle both struts and they seem loose then there isn't any pressure in either. The last suggestion I have is that theres a little plastic moulding inside the piston of the strut. It keeps the pushrod in the middle of the piston. However, if the pushrod is inserted wrongly or if the rod has become dislodged (which can happen with low pressure spheres) then it can catch the side of the plastic insert. The effect is that one pushrod effectively becomes longer than the other.

The only way to tell is dismantle the struts and inspect the inserts.

Cheers,

noz

[techmanagain]

Thank you Noz. That's a new one on me!

[kcleong18]

Hi noz & guys,thanks for the replies.
As techmanagain says that's a new one.Yesterday tried and found
that removing the whole rear cylinder as a unit is not possible without
separating the sphere ,which answer my own previous question.The
locking pin is actually easier than trying to refit the two hoses
especially with LHM everywhere and the job just two inches from your
nose.
I tried removing the piston rod and the gaiter but somehow did not
manage to maneuver it out so will try again in a couple of weeks.As far
as I can feel the pushrod seems to flop about at the piston end with no
indication of any centering device. After giving up and fixing everything back I added one more to the number of leaking points of my XM.
Prior to that I have also loosen all bolts of the anti roll bar
and after knocking the wheels/bar to settle any stress retighten them.
Now the difference of drop height between the two rear wheels is about
5 mm which to me is acceptable. I also noticed that jacking one wheel up causes only very small changes in the other wheel height ,rather the antiroll bar twisting to counteract the change. Thus rear height corrections are significant only if both wheels rotates. A big difference in height between the two sides can only cause the roll bar to twist and as such will not contribute to height correction.Will this
mean that a twisted anti roll bar is not such a big deal? My conclusion. Comments welcome.

Last thing here is the spheres. Although I have swapped them less
than a month back and tighten them 'hand tight' I broke the chain of my
el cheapo oil filter/sphere remover tool twice trying to remove them.Hence the idea of removing the rear cylinder as a whole unit.Did finally manage to crack the joint with a thicker replacement bicycle chain. Now I hand tighen the spheres and then undo them about twenty degrees for insurance.No leakage so will do for now.Hopes this help anybody changing spheres.

[noz]

Hi KCleong18,

To see the centering device it would be necesary to remove the rubber gaiter from the strut. It will be stuck at the inner end of the piston. You might need a torch to see it. If its not there then it is missing and may account for your height difference. Your adjustment may have only compensated for the missing piece.

When removing the rubber gaiter take care to mark the orientation of the return tube connection points. If you get the position slightly wrong it can make life very difficult when you come to reinsert the tubes in the holes. If you get the orientation correct then the tubes are actually quite easy to reinsert. If they were difficult as you have pointed out then it is possible a previous owner has not been careful about positioning the gaiter during a previous removal. To reposition, just loosen the wire clip and rotate the gaiter with respect to the cylinder until the tube holes are in an accessible location.

I understand what you mean about removing a sphere not long after you refitted it. However, I would not recommend the method of slackening by 20 degrees. It is possible the sphere could come loose in use. The tightness you found is caused by a thin film of rust between the shoulder of the sphere and the shoulder of the cylinder. A much better solution is to put a smear of grease on the mating surfaces and tighten by hand as normal. Even better would be to smear some grease or sealer around the joint once assembled on the car. Its a combination of water and oxygen which causes the problem and it can be avoided if you cover the joint with something to keep the water out.

cheers

noz

[kcleong18]

Hi guys,
Got a couple of holiday break so decides to swap rear cylinders.For completeness and before my memory lapse , the following are the steps I took to remove and reinstall them . This is how I did it on my car and for your reading pleasure and therefore may not be accurate or applicable to everyone.Usual caveat applies and errors are mine especially for terms used.Your comments are appreciated.A lot of thanks for the tips received and credits due acknowledged and I hope you guys do not mind if I used some of them in my notes. I do have some nice pictures of the innards but do not know whether they can be posted here.

Put car on high ,secure car on jack stands or other methods , crack spheres and high pressure pipe joint , set car to lowest height , open and close door while depressurising hydraulic system . Stop engine. Cylinders can now be rattled in
their cage if system is depressurized.I would have cleaned the area around rear cylinders prior to this ( I did not!!) to avoid LHM and goo everywhere.

Remove center muffler ( size 13) to improve access and also anchor points (size 10) of high pressure pipe.The latter will allow some movement of the HP pipe without undue stress. Lift the trailing arm of the relevant side with another jack
and remove piston 'R' locking pin. Remove clip retaining cylinder,sphere and unscrew high pressure pipe nut.Tie pipe to one side and cover joint to prevent dirt going in. Hold fulcrum end of piston rod while lowering jack and piston rod should pop out of cup in arm.Maneuver and rotate cylinder assembly to ease removal of vent and seepage hoses.Noz's post on this is great!It would be a great idea to note / photo / mark all hoses and rubber placement to facilitate refitting.The rear cylinder assembly from car can now be eased down and forward (of the car) out thru the cylinder cage.Reverse procedures when refitting.

Some notes here. Jacking the trailing arm allows the locking pin enough clearance to be removed and at the same time excess LHM to be pushed back to reservoir.Lowering it makes the piston rod end unseat from the arm .Be careful when removing/refitting vent / seepage plastic hoses as the gaiter fitting point shoulder will cracked and leaks LHM.Ask me how I know! Check that they are not rubbing against the edges of the cage and reposition the gaiter if needed.Incidently the gaiter has a locating inside tab that fits the cylinder seepage channel.

After dismantling, clean the cylinders and its component parts;piston rod ,rubber gaiter, piston (with centering plastic inside)and felt oil ring outside, cylinder with cage locating hub.There is quite a bit of black stuff inside both
cylinders.To separate and install the piston rod and gaiter push carefully thru the rubber gaiter .This is an example of 'reverse procedure' not working. I greased the flexible( ball joint?)rod end and cup end of the arm before refitting.Line up the holes with a piece of wire before inserting the 'R' locking clip.
Both rear cylinders are leaking quite badly ( about 2 drops per seconds ).The cylinders have two internal rings / seals at the bottom of the cylinder.The higher one is a white plastic ( teflon ??) square seal and the lower one is a black round rubber ring. My guess is the white seal is worn out . Wonder whether this a available as a repair kit.

I have everything refitted and checked for leaks.Both HP pipe nuts needed a bit more to stop some weeping.After all this exercise what do I get ? Exactly the same problem . Nearside rear still higher than offside.Since the XM is now not
exactly on perfectly level ground I will reconfirm measurements when I moved her to a different place. For now a bit of XM hydraulics burnout so will leave further investigation of this problem later.

Second edit here. Forgot to mention that preliminary measurements after swapping show front end having similar height discrepancies. Food for thought .

So then best regards to everyone.
kcleong

This post has been edited by kcleong18 on May 03, 2007 06:25 am