C5x7 front end knocking - anti roll bar subframe bushes?

[aerodynamica]

Hi all, I have been trying to trace the cause of a knocking at the front end. It is mostly towards the RHS, tends to be on sharp downwards bumps but also seems in some way to be related to engine torque and LH turns.....

I have replaced in recent months:

L& R lower control arms
L&R lower hub bush
L&R upper swivel balljoint
L&R lower swiver 'frip' joint
L&R inner track rod joint
L&R outer tie rod end
L&R anti roll bar droplinks
RH full driveshaft (LH 2 years ago)
upper engine support, torque bar
checked lower torque bar bushes
checked steering rack securing nuts
checked all front subframe mounting bolts
looked at upper suspension bushes and all appear good and there are no 'witness marks' I can see showing any play/ contact of adjacent parts.
looked at exhaust downpipe in case it was wobbling...
Mounted Gopro camera under the wheelarch looking for movement and not one clue found.
generally now out of ideas. The knocking is felt in the footwell area.

The single thing remaining that I can think of is the anti roll bar rubber bushes. These 'look' ok and I can't see any obvious issue with them. If I rock the car heavily inside the garage where I can hear things well, there is n knocking at all - only seems too be when driving.

Could it be the anti roll bar bushes? I might change these rubbers anyway but it does appear to be yet another subframe lowered job.

Has anyone done this job?

[mickthemaverick]

Having read all that the one thing you haven't changed are the wheels/bearing. Way back in the day on my Talbot Samba Rallye I had a knock which turned out to be a cracked alloy!!

[Steve Walsh]

Remove springs from the front shockers and check damping,

[aerodynamica]

Having read all that the one thing you haven't changed are the wheels/bearing. Way back in the day on my Talbot Samba Rallye I had a knock which turned out to be a cracked alloy!!

Gooooood suggestion! Both are unreplaced wheelbearings.

[aerodynamica]

Remove springs from the front shockers and check damping,

Ah, that's one thing that might not be to blame because my C5 is a hydropneumatic C5

[Kees]

It's possible, you should also look at the spheres special the corner ones.
Try to find a bump where you can test at several speeds and check the behavior when the car rolls of the bump.

[aerodynamica]

I hope it is not the spheres because they're less than 1 year old!

[aerodynamica]

Having read all that the one thing you haven't changed are the wheels/bearing. Way back in the day on my Talbot Samba Rallye I had a knock which turned out to be a cracked alloy!!

Also, how long was your alloy cracked before you found out

[mickthemaverick]

No idea on that one, but I found it about a fortnight after I started hearing the noise

[aerodynamica]

Well, it's still knocking. Occasionally a lot over little bumps. Sometimes it's quiet for ages then knocks once randomly. I had the chance to drive up on ramps again to look at a new steering leak................... that appears to be from one of the two thin pipes that go from the pinion housing to the rack, and to make a small adjustment to the new RH tie rod end. It was at that stage I noticed that any torque on the RH track rod caused some rotation at the LH trackrod! I only noticed as I happened to be holding it while adjusting the RH by a 1/4 turn. I think the steering rack is moving within the rack housing. Moves a small angle each way then stops. I assume because the spring plunger has loosened off? Or there is some other problem with the rack? I compared with the spare steering rack I have from Stu sloppysod, where I could loosen the plunger a bit to let the same rotating of the rack then tighten till it all but vanishes. Going too tight results in the steering being too stiff to turn so there is a sweet spot to turn the spring plunger. I tried in vain to get a 17mm socket to locate in the spring plunger of the rack in the car to try and tighten it a bit. It is just not possible with the subframe installed. I partly unscrewed the bolt that secures the rearmost bushing of the control arm as its protrusion prevented any possible tightening of the rack spring plunger but to no avail. I think the subframe will again have to be lowered.. I rebuilt the steering pinion valve over a year ago with a repaired cardan shaft, speedisleeve, new double shaft seals, modified pinion housing, a steering shaft gaiter and it is still all holding well. I did tighten the spring plunger while on the workbench at the time but could I have done something wrong? I didn't see any kind of 'peening' of the plunger's outer circumference to notch it in place over time. Perhaps it should have had. Anyway, I am getting a feeling that this rotating action of the rack is what is causing the knock.

I suppose lowering the front subframe must happen. I also realise the steering rack is fitted to the subframe with the two long threaded rods and a flange nut each. There is also a thick washer for each. I refitted these last year in the same place they were when I removed it - under the flange nuts - but I saw a parts diagram on here of the parts and they are described as adjusting shims. I see they have a face pattern that would match the mating face of the rack mounting that leads me to think they really should be fitted between the rack mounts and the subframe instead.

Does anyone have access to the fitting guides to confirm this?

[aerodynamica]

I've learned that these washers do indeed fit under the steering rack.