Xantia noisy over bumps

[peter306]

Iain, ordered that set from the link.
Happily i'm getting quite good at taking the trailing arm off, it's getting the thing back on is the pain

I shall post the result when it's done

Peter

[Stickyfinger]

Do these need final tightening with the car on its wheels so there is no "stress" built in ??.... in the same way as other suspension joints

[peter306]

Alasdair,
not to my knowledge, no tensioned rubber involved but the car is on ramps so had the weight on the wheels.
Peter

[wurlycorner]

Yep, as Peter says - doesn't matter what position they're tightened in, because the load is only pre-tension axial load through the taper. They never see a 'torsion' load, because they're bearings and rotate freely

[aerodynamica]

Do these need final tightening with the car on its wheels so there is no "stress" built in ??.... in the same way as other suspension joints

What Iain said, the axial load is pretty high if I recall. I can't recall the final torque the 24mm nut goes to but I think it was quite high. On the CX there was also a shim or two added between the thrust bearing and the mating face of the subframe that accounted for the correct load when the thing was torqued up - there was some protrusion of the support tube to measure I recall. personally, I just replaced the same shims as came out it in the first place..... Not sure why the Xantia didn't need this same attention. Perhaps the subframe and arms were more accurately machined in the factory.

[wurlycorner]

Not sure why the Xantia didn't need this same attention. Perhaps the subframe and arms were more accurately machined in the factory.

Yes, I presumed that also - or the difference that CX arms are aluminium where Xantia are steel (perhaps concern the inner bore shoulder the outer race sits against, might deform over time and change the offset?)

[aerodynamica]

Right enough Iain, that's possible. I really disliked those rear arms on the CX. Alloy arms with a hollow center that was open to the back of the wheel bearing so that any water that got in just sat there behind the bearing... not to mention the two different sized bolts that fitted the anti roll bar to the rear arm, the alloy and steel bolt sometimes corroded and welded together with the bolt breaking in the casting... More shims fitted to the anti roll bar mounting block.. Also! the CX rear arm bearings were harder to remove because the bore in the casting between the sides was narrower than BX, XM, Xantia so you needed to weld a bit of metal to the old bearing race to use to drift it out from the other side. Still, I did love them so..

[wurlycorner]

Yep - the type of seals on the CX arms are crap compared to Xantia's, too.
I had an anti-roll bar bolt strip out the arm once (not the end of the world - just drill and tap with a heli-coil) and a couple shear off. One I was fortunate enough to be at university at the time, so carried it an hour in (that was a heavy/awkward rucksack) and used a spark-eroder to remove with no damage to the arm, but another I was on my drive years later and had to resort to hand drilling

[peter306]

Well I got the trailing arm back in position, all new bearings and bits. Still making the clunky/clicky noise when bounced.
Alasdair, they are tightened up to 130 Newton Metres,
It's still on ramps so i'm going to get an automotive stethoscope and investigate further, did try with the screwdriver in ear method but as some bits move when you bounce it there was a slight "ouch" factor.

Peter

[aerodynamica]

I wonder if the noise is from the push rod of the suspension cylinder. The end that locates in the arm has a kind of bearing that could be worn. I know it's a common issue on DSs but they have a different structure in that area.

[peter306]

Graeme, the cylinder and pushrod is the area i'll be looking at when the scope arrives, only moving thing left that I can think of.

Peter

[peter306]

The push rod is very loose in the cup, with pressure off I can replicate the noise when the push rod hits the wall of the ram. How tight a fit is the ram supposed to be in the cylinder bore as I also noticed that the ram has slight lateral movement in the end of the cylinder bore, this also replicates the noise when it hits the side of the cylinder, a bit like the piston slap principal.
As the noise is only there when the wheel drops of an edge or into a pothole not in normal driving i'm working on the theory that the trailing arm pulls the rod away from the ram and there is a reduction in pressure before the dog bone opens the valve.
Any other theories gratefully received.

Peter

[wurlycorner]

That rod is specifically why I asked if the noise was present with the suspension pressurised or depressurised.
With the wheel on the deck and the suspension pressurised, it shouldn’t be possible for that rod to make a noise just from someone pressuring the back of the car up and down.

[peter306]

Iain,
It's going in for the mot tomorrow, once that's done i'll be taking the that cylinder off and checking all the bits for fit.
I'll also be checking the pump as if that is not working properly (188.000 miles) might be a bit worn and not delivering what it should.
As the system is reactive these are the only things I can think of.
As previously said all other theories gratefully received

Peter

[aerodynamica]

Hi Peter, good luck with the MOT, my 2008 C5x7 just flew through the MOT with nothing but an advisory... not bad for an 18 year old.
I agree again with Iain, and there should be no aspect of any of it that can be moved by hand when its standing on its wheels. Unless the system is depressurised and it is down on the rubber stops where the cylinders can be 'loose' but their movement will still be very restricted.

If I get you right you're asking if the hydraulic cylinder ram can have movement separate from the pushrod within it. Certainly not - these are a very precise fit like all the Citroen hydraulic moving parts. Their sealing is achieved by super precise fit (10ths of a micron) even the suspension cylinder. It is designed to leak LHM but this leakage is the result of fluid effectively 'osmosing' slowly over the fit of these various micron tight parts like rams and slide valves etc. Anything more loose than the precise fit caused by e.g long term wear, would be bad.

That said, my first CX, a 1978 CX 2400 C-Matic I had in 1999, was in a poor state. One of the rear cylinders had a bore that had indeed worn and was ovoid in shape and interestingly it didn't appear to leak. It didn't sink down excessively fast or anything.. But even so the ram wasn't actually sideways moveable in the cylinder.

Noises can be difficult to trace. I currently have an irregular knock at the front on the C5. I can't find it. both lower control arms are new, the lower outer bush is new, both lower hub swivels (frip joints) are new, both upper swivels are new, the inner track rod joints are new, the tie rod ends are new, I checked the lower engine torque bar, jut replaced the upper torque bar, checked all subframe bolts, checked the steering rack mounting nuts, looked at the RH driveshaft support bearing, the LH driveshaft is new, looked at the upper suspension arm bushings - not new but no sign of movement. Front drop links were changed 3 years ago and don't appear to have any wear and in any event the knock is not 'only going over bumps' it seems to be occasional for bumps and at times a single clonk driving straight, other times low speed steering clonk that only happens once ... so I'm with you when it comes to an annoying knock that you just can't locate.