Vibration in rear of car

[richard]

This has been an ongoing topic for some time, however, searching through this forum, it never appears there is a definitive answer which solves this problem.

We all appear to have cars which vibrate between 65 to 70 miles per hour. Certainly we can't all be having tires needing better balancing, or tires out of round, or cheap tires, or wheels which wobble. There must be something we're are overlooking, like motion in the rear suspension. Has anyone put their car on a dyno and run the car up to speed?

When a solution is found it should be posted on the forum, rather leaving it open ended.

[Robbie693]

Hi Richard,

I had a vibration around a slightly higher speed for a long time, I may have posted about it too but don't remember(!) but what I have found is that various things had an effect on lessening the problem which may be why many posts on here are unresolved - the symptoms are caused by more than one thing and the owners are still working through chasing problems. Or, something is changed and this improves matters, owner thinks he's found the cure, only to realise later that when something else is changed that thing makes it even better!

For my part, I found replacing the gearbox mounting helped and I thought that was as good as it was going to get, but then some time later I had the clutch replaced as it failed and that made things even smoother. Which was a bonus!

Robbie

[GuyC]

Hello Richard,

I've not got an answer but do have the problem! It's nearly exactly as you describe except around 70-75mph. It comes through the base of the seat and a bit into the steering wheel and is completely vehicle speed related, not engine.

I will be getting my wheels balanced this afternoon and will report back if this solves it. Given how substantial it is I would be surprised if it is just balancing, so suspect it is driveline related. I will be watching this thread with interest...

Robbie,

Is the gearbox mounting fairly accessible? I've also read that a spacer there can help too.

Cheers,

Guy

[richard]

It would be nice if we all had a check off list posted. For example, how many of us started having problems after the:
1.deferential removed
2. drive shaft removed
3. marked drive shaft before removing

There are companies which have modern equipment for balancing drive shafts. Usually located around race tracks, and one of the interesting suggestions this company had was to first take the shaft out and swap it end for end -180 degrees - before sending it to be balanced. Beyond my comprehension but wort a try. This is a bigger vibration than just solved by balancing wheels.... i've tried.

Richard

[AHM]

1St question is CV joints or doughnuts fitted?

[englishmaninwales]

I had a marked vibration in my S3 at 50 to 70. Tried checking all the usual causes, but not resolved. When the engine was out and being rebuilt, I took the clutch, flywheel, crank, pulley an rod/piston assemblies to an old school engine balancer. He commented the crank was pretty awful, as was the clutch pressure plate. All was balanced, producing a nice smooth engine and the vibration has gone.

[Robbie693]

Robbie,

Is the gearbox mounting fairly accessible? I've also read that a spacer there can help too.

Cheers,

Guy

Yes, it just unbolts from underneath. Support the gearbox and remove the mount.

I suppose any engine vibrations could be isolated by disengaging the clutch at the vibration speed and see if it goes away?

Robbie

[AdrianSi]

I've got the same problem, and having just driven from the UK to Le Mans Classic and back, is high on my to do list. The vibration on mine is as above, seems to be through the tunnel and is definitely driveline related.

When I dip the clutch and take it out of gear, the vibration doesn't change at all, which points towards propshaft issues. I don't think it is a wheel balance issue as it doesn't feel to be front or rear related.

I think i'm going to be tempted to mark and rotate the propshaft around and see if it alters the vibration.

[worzel]

Hi

Are you sure the diff isn't making contact with the frame?


Regards


John

[jono]

No such issues with my Plus 2, though I did have the prop balanced and new joints fitted by a prop specialist when I built it.

I also seem to recall that whilst the prop runs at a slight angle it's necessary to have the mounting flanges at the diff end and gearbox parallel to keep the prop joints 'in phase'.

I'm no engineer but I did take this on board and took care to ensure this requirement was met (as close as I could) when I built the car, though I have no idea if this is why I do not have a vibration issue.

..another thing to consider perhaps?

Jon

[AdrianSi]

Hi John
In my case this isn't a noise, is definitely something that isn't balanced after the clutch.

[frogeyesimon]

I had much the same symptoms. Had the wheels balanced & re-balanced without much noticible improvement. In the end a trial-and-error swapping of the wheels around the car has improved things. Still not perfect though.
Simon

[rgh0]

Built it right and balance it right and it does not vibrate ---- at least my plus 2 does not

It is just a machine and there is no magic about it, but it does take a lot of detail to be right.

You just need to work through every element that moves and ask those questions "is it built right and is it balanced right". Any vibration will be because one of the answer to that question about one or more components is no. The average mechanic struggles to answer those questions so getting the right advice is hard

Lots of components and lots of possible reasons to answer no -- so no simple magic bullet.

cheers
Rohan

[jono]

Rohan,

Your maxim make me feel very proud - I'm not an engineer (I'm a surveyor) but I built my Plus 2 from scratch down to every single nut and bolt including the engine and it doesn't vibrate, in fact it very smooth and the faster it goes the smoother it gets

I am however a perfectionist who leaves nothing to chance and perhaps therein lies the secret

Jon

[Daugaard]

Also had vibrations in my 68 +2 at the same speed.
Found it came from a worn bearing housing in the rear left strut.
The bearing could just slip around ind the housing.
Got an other, changed the ball bearing and the vibration were gone.
Then I noticed a small vibrating from the front of the car at another speed.
The rubber bushings in the torsion bar is gone so need to change them.
Suspect that could easily be the case when vibrating occurs and the source is hard to find.

Jens