940 transmission vibration - prop shaft or differential?

[martin calva]

Originally Posted by 360beast

Propshaft vibration is most prominent when setting off from a standstill or when reaching certain speeds.

Did you ascertain whether or not your car has the updated strut rods and are the bushes for the front suspension in good condition? Also when was the tracking done? Are the front wheels balanced/buckled? All of those will affect vibration when braking.

My 940 is very susceptible to braking vibration if the wheel alignment is out, maybe it is to do with the polybushes but twice I've had the front suspension apart requiring a wheel alignment and both times before having the tracking done it got a bad braking vibration.

When they've got the car on ramps have they got the rear wheels hanging down or is it jacked up on the rear axle? If the wheels are hangin down this would put the propshaft at an extreme angle inducing a vibration.

Thank you for those comments.

[1] I asked about strut rods but (my French is only 75%) I did not get a clear answer. My guess is the strut rods are what was originally fitted to the car. The garage says all bushes are in good shape (they replaced bushes in the suspension triangle).

[2] Wheel alignment has not been checked as such. The April 2023 Controle Technique measured the misalignment/drift as negligible (drift = 2.9m /km)

[3] All wheels have recently fitted tyres which were balanced on fitting. The wheels are cast aluminium and are not visibly buckled. That will have been checked along at the C.T.

[4] Wheels are hanging down when on the lift. I'll ask them to try with the weight on the rear axle.

This is a problem that has appeared, getting progressively worse, since April. So something has deteriorated. I'll just mention again that the vibration on braking is a very severe and alarming juddering - not just merely a noticeable vibration.

Thank you again.
Martin

[classicswede]

Originally Posted by martin calva

Thank you for that. I am grateful for all your comments which I know are based on your wide experience.

There are two symptoms and I (and the garage) assume they are related:

[1] With the car on a lift and the rear wheels rotating in free air, continuous vibration at prop shaft speed is noticeable when a hand is placed on the centre bearing or on the rear axle. The garage owner said that this vibration is due either to a prop shaft problem or it is due to a problem in the rear axle.

[2] With the car running at speed, in gear or in neutral, there is horrendous juddering vibration when braking.

I am waiting for the garage to see whether the continuous vibration is still present when the rear half of the prop shaft is removed. If it disappears, that will suggest to me that the rear axle has a problem which is causing the continual vibration.

I have been given a back axle from a 2.4 diesel which had done 250,000 miles and I note that it has no discernible play when I twiddle the prop shaft coupling. Whereas the rear axle on my car has very significant play when I twiddle the prop shaft (gear in neutral).

Is such play normal and acceptable? Could it be the cause of my problems?



I wondered about that. The garage says that the torque rod bushes are in good shape.

1) if the prop vibrates with the wheels hanging down that is perfectly normal. If you want to simulate running you need to put jacks under the axle to hold it up. If on a 2 post ramp I would suggest jacks also under the front of the car

2) is the vibration coming from front or rear of the car? Can you feel it through the steering or through the seat? With it only being under braking that suggest a bush is compressing putting wheels/prop out of line.

Lash is normal in the axle and gearbox. On the car the two combined will make it feel twice as much. When you get to much lash you will get a knock under acceleration /deceleration

[john.wigley]

Originally Posted by martin calva

John, thank you for those comments.

The garage found that, with the car on a lift and the wheels rotating in free air, there was noticeable ongoing vibration at prop shaft speed that could be felt by putting a hand on the centre bearing or on the back axle. The garage owner stated that the problem was either due to the prop shaft or to the back axle.

They replaced the rear half of the prop shaft with one I had received and that made no difference. (The front half I received was wrong for my car).

I have been given a back axle from a similar car and there is no discernible play when I twiddle the input shaft. Whereas the prob shaft on my car has very noticeable play when I twiddle the prop shaft. Could this indicate that the back axle is causing the problem?

There is very serious juddering vibration when braking yet no noticeable vibration when driving normally. Is that consistent with an out of balance prop?

I'll bow to others' superior knowledge, Martin, and feel both 'classicswede' and '360beast' have already provided better answers / explanations that I am capable of.

However, since you posed two questions to me directly, this would be my take on the situation.

1. The axle that you have acquired would appear noticeably less worn than the one presently on your car with probably a much lower mileage. As such, it would certainly make a good spare to use should your present one fail. Whether the wear / play / lash in your present one would cause the vibration, I wouldn't like to say.

2. I would expect vibration due to an OOB prop to be present under all driving conditions and to vary with speed. I would not expect it to be greater when braking. The 'very serious juddering vibration when braking' that you mention makes me think of warped discs. Does the degree / intensity of the vibration vary with the rate of deceleration, i.e. between gentle 'check' braking and hard 'emergency' braking?

Regards, John.

[martin calva]

Originally Posted by john.wigley

I'll bow to others' superior knowledge, Martin, and feel both 'classicswede' and '360beast' have already provided better answers / explanations that I am capable of.

However, since you posed two questions to me directly, this would be my take on the situation.

1. The axle that you have acquired would appear noticeably less worn than the one presently on your car with probably a much lower mileage. As such, it would certainly make a good spare to use should your present one fail. Whether the wear / play / lash in your present one would cause the vibration, I wouldn't like to say.

2. I would expect vibration due to an OOB prop to be present under all driving conditions and to vary with speed. I would not expect it to be greater when braking. The 'very serious juddering vibration when braking' that you mention makes me think of warped discs. Does the degree / intensity of the vibration vary with the rate of deceleration, i.e. between gentle 'check' braking and hard 'emergency' braking?

Regards, John.

John, many thanks.

The severe juddering occurs under normal hard braking such as when leaving the French auto route, slowing from 65 mph to 30 mph on the slip road (French autoroute slip roads are much shorter than in Britain),

Essentially no vibration when slowing gently from moderate speed - this suggests to me that it is a positive feedback effect involving play or backlash in the system somewhere or other in the system.

I changed the front disks when the vibration first appeared, assuming the front disks were warped. The vibration was still there, so I installed Bosch disks. The vibration was still there, so I bought a run-out micrometer. The run out measure 0.01 mm on one side, 0.02 mm the other side. Less than the 0.06 mm that Volvo say is tolerable.

The garage said there was slight play in the triangle bush - so they replaced those (400€). No effect - still serious vibration.

The garage owner suggested it could be the front wheel bearings. So I ordered new bearings (166€ Skandix - less than the 600 € of the garage's normal supplier) and the garage installed them - no change, still serious vibration.

The juddering seems to be the whole car - it does not seem to come from the steering wheel nor from the brake pedal. So not obvious where it originates.

As always I am grateful for all comments and suggestions.

Martin

[martin calva]

Following advice given here, I asked the garage to replace the torque rod bushings. They have come back to me saying that their parts supplier cannot furnish them. I told them I'd do my best to find them from another supplier.

On Skandix I find "1001279 1229608 Bushing, Suspension Rear axle Pull rod front round" (out of stock but available from other suppliers)

And "1001280 1272306 Bushing, Suspension Rear axle Pull rod rear Convex"

(I assume "Pull rod on Skandix" means "Torque rod" here.)

My question. Are the bushes for the upper and lower torque rods the same?

Thank you for any advice.
Martin

[Rversteeg]

1229608 and 1272306 are different bushings, see attachment.
Both available ex stock from various suppliers here in The Netherlands, for example www.estateservices.nl. Being in France, delivery is no problem.
I have had mine replaced last year, which completely eliminated the first gear prop shaft vibrations when accelerating from standstill.

[martin calva]

Originally Posted by baggy798

How are your torque rod bushings? They determine the angle of the prop in relation to the diff. Too much movement one way or the other due to wear can induce vibration.

Thank you for asking. I finally tracked down torque rod bushings (Skandix was out of stock on one of the sizes). The garage replaced them. But STILL bad vibration under braking.

[martin calva]

Originally Posted by martin calva

Following advice given here, I asked the garage to replace the torque rod bushings. They have come back to me saying that their parts supplier cannot furnish them. I told them I'd do my best to find them from another supplier.

(snip)

My question. Are the bushes for the upper and lower torque rods the same?

Thank you for any advice.
Martin

To answer my own question, Skandix confirmed that upper and lower torque rod bushings are the same.

[martin calva]

Originally Posted by john.wigley

Hello Martin, I think that you are bang on the money with the prop centre bearing. In an age of predominantly front wheel drive, there are far fewer mechanics who have experience of and understand rear wheel drive issues.

In the past, I've experienced similar issues on earlier cars - all caused by a failed centre bearing.

Regards, John.

John, thank you again for that, I obtained a new centre bearing, the garage fitted it but reported STILL bad vibration under heavy braking.

[Baffler]

You're not having much joy with this one, Martin, all credit to you for your perseverance!

Stumbled on this old thread, started by Pete940, which may be of interest to you:

https://www.volvoforums.org.uk/showthread.php?t=194297

Pay particular attention to post #14 and check your spline/UJ tab is located/aligned correctly against the shaft keyway to obtain factory setting.

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?