High speed vibration - possible causes ?

keanej

keanej

New Member
3500 Auto, had really bad vibration at high speed, have replaced UniJ on prop and half shaft along with a duff Diff mounting rubber and gear box mounts ( and did a quick job on the rear suspension with poly bushes while I was at it - amazing change to the feel on bends !! )

Went for a test drive on Saturday, the vibration is greatly reduced and definately none from the rear now, however still some from the front.

Checked all the obvious, wheel balancing, bearing play, although it doesn't feel through the steering wheel.

What else should I check, engine mounts - could this cause it ?

Ball Joints ? - Can anyone tell me how you should check these, I can't feel any play

Any ideas ?
 
hi,
have you checked the shock absorber bushes as you will not like you say feel that through the steering wheel.

ianp6man
 
Also check that all bodywork is secure, loose panels can start to vibrate at high speeds. Number plates are often loose.

Richard
 
Thanks for the pointers

Checked the steering ball joints and engine mounts - all OK

Some play in the bottom shock rubber bushes, more on one side than the other, although not exactly floating around - could this really cause the whole of the front of the car to shake on the motorway ? its reasonably stable within legal limits ! - Are these available as separate items or do I need to buy new shocks ? at least it looks like one of the easiest jobs to do

Gave all the panels a good pull none are loose, bonnet feels firm when closed.

One item that could be of concern is a lower suspension bush - the one on the arm that runs from the back of the engine bay and fits via a small ball joint to the bottom suspension link - some perishing on the edge but other than that feels solid

Any other ideas would be appreciated
 
You say this vibration is not felt through the steering?

Most of the problems offered definitely would be, certainly any balance problems with the wheels.

Best idea I can offer is to check the wheels / tyres for roundness - many tyres suffer from this either through poor manufacture (cheap tyre), poor fitting or simply age. It is not shown up under balance checks! Just simply jack the car and spin the wheel against a fixed pointer (eg pencil) pointing against the tread.

The effect can be similar to poor dampers - the wheel is effectively pattering on the road.

There is a varaition on this theme where the wheel / tyre are not running true - but this would definitely show in the steering.

Chris
 
Got some poly bushes, came next day so took the shocks off on Saturday......

As for the shocks - One side seem to have resistance ( opening and closing ) but probably not enough. The other side had some resistance on opening but none on closing - so this looks to be the cause. I won't get chance to replace them for a couple of weeks - so I'll update once I've fitted new ones

Interestingly the standard test i.e. bouncing the wing shows that they are OK
 
Just a quick update

Fitted new shocks and they reduced the affect of the vibration but it was still there.

Turns out it was the prop shaft needing balancing.

Local company Firow Ltd sorted it, chap picked it up on his way to work on Wednesday and dropped it off on his way home the same day.

Quick test drive tonight shows its now fine.

Just need to tighten all the bits of dash that had become loose through the vibration now !
 
Fascinating! Now that's something that isn't supposed to be possible for a P6. Body mounted diff ought to make it immune to that sort of problem. Perhaps somebody changed the UJ's at some point and got them back together 90 deg out?

Just goes to show there's no such thing as can't in engineering!

Chris York
 
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