940 transmission vibration - prop shaft or differential?

[martin calva]

Originally Posted by Baffler

You're not having much joy with this one, Martin, all credit to you for your perseverance!
(snip)
If all is well with the spine/UJ is it possible the propshaft has lost a balance weight along the way and would it be possible to have the complete prop rebalanced?

Thank you. It definitely has been going on longer than I would have liked.

I can't rule out anything that has not yet been tried. But I should mention that there is no sign of vibration when running at any speed without the brakes being applied, which seems to me to indicate that it is not a problem of prop shaft balance.

The effect is strong, almost frightening juddering when braking hard from speed.

In one hour I have a rendevous arranged at the garage to discuss with the owner (a former Volvo employee) and the mechanic, what they propose to do to resolve the problem. Run it on a brake test rig? Install a video camera to watch the front/rear suspension? Swap engine/gearbox supports? ....(Although, on reflection, since it happens when coasting from speed in neutral, engine supports seem unlikely to be the culprit.)

[Rversteeg]

Have the rear brake discs been replaced? It seems like when braking hard something starts to resonate. Resonation is always a combination of factors, take away one factor and the resonance will be gone. Could be an uneven braking, rubber suspension part, shock absorber...

[360beast]

Could it be something to do with the ABS kicking in and out when it shouldn't?

[classicswede]

Originally Posted by 360beast

Could it be something to do with the ABS kicking in and out when it shouldn't?

Good point. I remember a few years having a 850 that you could feel the brakes pulse side to side. i was certain it was a ABS problem but turned out to be a issue with new front calipers!

The ABS is a good shout and I would pull the fuses out to test if that changes the problem. Quick and easy to do

[martin calva]

Originally Posted by classicswede

Good point. I remember a few years having a 850 that you could feel the brakes pulse side to side. i was certain it was a ABS problem but turned out to be a issue with new front calipers!

The ABS is a good shout and I would pull the fuses out to test if that changes the problem. Quick and easy to do

Some time back (months ago) I disabled the ABS to see if that was it. Also disabled the power steering. Still serious vibration without ABS.

I asked the garage to try disabling the ABS and, to my recollection, they did and it had no effect.

[martin calva]

Four weeks ago, the owner of the garage said that they would try fitting the rear axle I had obtained. I asked why he thought that would solve the problem. "Because we have tried everything else". My car stood in their yard for 3½ weeks. Finally they swapped the back axle. Yesterday the chief mechanic phoned me. The rear axle works fine, but still serious vibration on braking.

They are now suggesting giving me back my car, still with its vibration problem, and calling it quits. That would still leave me without the car in usable condition.

I plan to tell them that the problem must be solvable and, as Volvo experts, I expect them to find the solution. It's pretty clearly something that they think is in good condition is causing the problem.

Some things they have not changed or done:

- rear brake disks and/or calipers
- front wheel alignment/balancing
- front shock absorbers
- rotules (I forgot the English name - the rotating joints at the front)

As always, I'll be grateful for any suggestions. Not having the 940 is a big problem for me I will not use my beautiful V90 to cart tons of building rubble to the dump etc etc.

As always, I will be immensely grateful for any ideas or suggestions.

Martin

[Rversteeg]

Given the relatively low price of a set of rear disks, I would give new ones a try, especially as it seems braking related.

[martin calva]

Originally Posted by Rversteeg

Have the rear brake discs been replaced? It seems like when braking hard something starts to resonate. Resonation is always a combination of factors, take away one factor and the resonance will be gone. Could be an uneven braking, rubber suspension part, shock absorber...

The rear disks have not been replaced since the trouble started. Something to think about.

[martin calva]

OK - I went to the garage and tried driving the car myself.

They had swapped the rear axle. On driving the car at very low speed, I noticed a 'clunk' from the rear whenever I put my foot down on the accelerator or whenever I lifted it from the accelerator. So apparently something not done up tightly or loose at the rear. I left them with the car on a hoist, investigating the clunk

On driving the car at 100 kph (60 mph) and braking, there was some vibration but nothing like what there has been before.

On braking lightly at low speed there was now some gentle vibration and, with hands off the wheel, some gentle rotary oscillation of the steering wheel. I now suspect there may have been two problems, one of which probably has been resolved - perhaps when the rear tie rod bushes were replaced.

I agreed to go back in January when they reopen and try driving the car on the open road where I can try braking hard from high speeds and be certain that the original problem of very severe vibration has gone.

Martin