(I'm picking up) BAD VIBRATIONS *the answer lies within!*

[Piston broke]

Hello everyone. I'm aware there's a long thread about this already but I think this may be different...

I have a horrendous vibration at just over 40 mph.

Here's a bit about the car-

It has just had the following:
Marina engine and new rubber mounts
New rubber gearbox mounts
New Mmc toughened half shafts
A 3.9 diff of unknown condition.

The symptoms appear even when cruising down hill at 40 plus.
Before conversion the problem was not as bad but the gearbox mounts were perished as were engine mounts.
I have just changed the universal joints but think it feels worse (have tried reconnecting prop after 180 degree turn but have in best position)!

My questions-
Do you think it's the prop in need of a balance?
Could the diff cause this- it does not rumble or whine?
Could it be the brand new half shafts?
Any other ideas please?!!!!

Cheers!

PB.

[beero]

Put the back axle up on stands, chock the front wheels and run the car up to 40. This should eliminate anything from the front wheels and you may be able to see where the vibration is. Are the wheels all balanced?
Has the car been stood for a long time in the same place because tyres can get a flat spot when stood too long?

[Piston broke]

I like that idea! Wheels are all balanced. Tracking has been done with in last year too but I'm all for ruling things out ( hence the UJ change in the cold rain today...!)

Will try tomorrow...

Thank you.

Pb

[bmcecosse]

Some of the new engine/box mounts are hard as rocks these days - maybe that's the problem?

[Tom and Maria]

I fitted new engine mounts and after a ten mile drive worrying that the car was shaking itself to bits I fitted the old ones again, problem solved.

Worth a try?

Tom

[JOWETTJAVELIN]

Undoubtedly the new engine and gearbox mounts. Put the old ones back in (as long as they're not disintegrating).

[Piston broke]

Hummm...

It does it when engine is idling and I'm out of gear doing 40 plus...
Idle and rev whilst stationary does not produce anywhere near the same type of vibration!
True, noticeably more vibe since the new mounts. But I'm sure it's not the mounts. Well. A bit sure. Ish.

[beero]

If it is the prop then harder mounts would transfer the vibrations to the body more, old soft mounts would absorb it.

[David53]

It will be the propshaft and/or Uni joints. Been through this with both my cars recently. Get the propshaft balanced and have new joints fitted, that should solve your problem.

[Piston broke]

Right. Here's today's post-test update!!

Had car on axle stands and ran it up to 45 in 4th.

Bad vibrations!

Ok. I'm veering towards the prop shaft theory but am not 100% sure about my diff.

When it was jacked up, and in gear, I revved up to 40. I video'd this on my phone. When I eased off and left in gear running on idle, the offside wheel stopped- but the near side wheel continued moving on idle. Is this right?

Prop shaft or diff or both people's????!!!

[beero]

When it was jacked up, and in gear, I revved up to 40. I video'd this on my phone. When I eased off and left in gear running on idle, the offside wheel stopped- but the near side wheel continued moving on idle. Is this right?

That's normal.

Did you remove the wheels? To rule them out of the vibrations.

[Piston broke]

[/quote]


Did you remove the wheels? To rule them out of the vibrations.[/quote]

Oh £&#*. Never thought of that.... And it's raining now....

[Piston broke]

Ok. Rain stopped for 5 mins.

Wheels off- still terrible.

Prob needs balancing I guess!!!

[Bazzalucas]

I hate to say it but if the vibes weren't here before the "new" diff, then it seems like the likely culprit.

[Piston broke]

I hate to say it but if the vibes weren't here before the "new" diff, then it seems like the likely culprit.

Oh well. Easier to sort than getting the prop shaft done...

I will try n borrow a diff next week and test your theory!!

Any other opinions anyone???

[bmcecosse]

Always go back a step when you hit problems. I believe it's highly unlikey to be a problem with the prop shaft - provided the U joints are not badly worn. So yes -try another final drive. But also check in case the half-shafts are bent....

[David53]

Unusual for it to be the diff, unless the front pinion bearing is shot and allowing the shaft to bounce around when its turning - My money is on the propshaft. I have had two cars in the last couple of years with this issue. Once the shaft is professionally straightened & balanced and new joints fitted the car should be smooth as silk.

[Bazzalucas]

I am only the voice of doom in this regard because I had almost the same symptoms right after fitting a 3.7 diff. No other changes that could account for it, and I tried "rotating" the driveshaft, replaced the U-Joints, etc. I have the same vibration (feel it right through the gearstick on the overrun) at around 50 mph as you describe. I sure hope I'm wrong- in both our cases- and that it is something easy instead.

[David53]

One other thing you could try. Undo the propshaft from the diff, rotate it 180 degrees and re attach. Make sure all four bolts are done up evenly and the end of the shaft is square on the diff mount.

[Bazzalucas]

He indicated he'd done that in his original post.