940 Intractable Vibration on Braking Problem

[360beast]

Originally Posted by martin calva

OK - the smile on my face is starting to wear a little thin. Between us, the garage and I have changed the following, but still bad vibration on braking:

- Front disks changed (twice) including using Bosch disks.
- Rubber joints in the front suspension triangles (not sure if that is the right name) replaced after slight play found.
- Right hand rear half shaft found to be bent replaced.
- Latest attempt - front wheel bearings and hubs replaced. Fortunately I insisted on using hubs from Skandix (160€ the pair) rather than from the garage's supplier (600€ the pair).

*STILL* bad vibration on braking. Any suggestions on how to diagnose the problem rather than just trying further things more or less at random will be gratefully received.

Martin

It's probably due to the strut rods like I linked to above, measure the length of yours, if they aren't 388.5mm long then that's most likely the cause of the vibration.

[martin calva]

Originally Posted by 360beast

It's probably due to the strut rods like I linked to above, measure the length of yours, if they aren't 388.5mm long then that's most likely the cause of the vibration.

Many thanks. I'll discuss with the garage this afternoon.

The problem appeared a few months ago then got progressively worse so, even if the strut rods are the wrong length, then something else must have changed to make the problem apparent. But if correcting the length of the strut rods solves the problem, then that will be great.
Martin

[Baffler]

Hey Martin,

I know it's a different beast but had a similar issue when breaking with my S80 back in 2019. Replaced the following:

Disks and pads front and rear (ATE).
Front bottom ball joints (Lemförder).
Front wheel bearings (SKF).
NS driveshaft (J&R).

Front control arm bushes were in very good condition with little travel.

All four brake calipers traveling nice and free.

No noticeable play in the inner tie rods or outer track rods.

Vibration still there. Swapped the front brake disks around...still there. Baffled!

Had my tyre chap balance all four wheels, fit the fronts to the rear and vice versa. Still present but vastly improved after balancing. You may wish to consider this if not already done so.

Whilst there I asked him to carry out a four wheel laser alignment and, with the car in the air, we discovered some play (gear lash) in the steering rack. I brought the car home and managed to get some adjustment on the rack and pinion. Sorted!

Not sure if the 900 has this rack adjustment but just thought I'd share my experience.

[TonyS9]

My next suggestion is bent rims, although this isn't as related to braking as bearing or disks.

Inner rims are less supported as more prone to bending, then there is tyres and worn bolt holes leading to off centre. MAybe try swapping wheels back to front.

Balancing won't correct off centre running when on the ground.

[Rversteeg]

When I had my front disks replaced some time ago I too had vibration issues when braking from higher speeds. I did not come round to sorting it out for some time and forgot about it. I now realize that the vibrations have cured itself without anything done. Apperantly it is a delicate balance of brake pads, disks, wheels, steering rack and rubber parts in the front suspension.
A long time ago I had the same issues and had the fairly new disks reworked by a professional brake workshop. It cured the vibrations for some 1500 miles before they came back again. I seem to recall that the disks were Brembo and the man from the workshop was a bit mystical by saying "I won't comment on that make". He did say that besides 940 also the Opel/Vauxhall Omega had similar issues. In the end by having them repaced by OEM Volvo pads / disks I got rid of any braking vibrations. That was over 15 years ago, not sure what Volvo would supply as OEM these days...

[360beast]

Originally Posted by Rversteeg

When I had my front disks replaced some time ago I too had vibration issues when braking from higher speeds. I did not come round to sorting it out for some time and forgot about it. I now realize that the vibrations have cured itself without anything done. Apperantly it is a delicate balance of brake pads, disks, wheels, steering rack and rubber parts in the front suspension.
A long time ago I had the same issues and had the fairly new disks reworked by a professional brake workshop. It cured the vibrations for some 1500 miles before they came back again. I seem to recall that the disks were Brembo and the man from the workshop was a bit mystical by saying "I won't comment on that make". He did say that besides 940 also the Opel/Vauxhall Omega had similar issues. In the end by having them repaced by OEM Volvo pads / disks I got rid of any braking vibrations. That was over 15 years ago, not sure what Volvo would supply as OEM these days...

Made in China junk

[martin calva]

Originally Posted by Baffler

Hey Martin,

Had my tyre chap balance all four wheels, fit the fronts to the rear and vice versa. Still present but vastly improved after balancing. You may wish to consider this if not already done so.

Whilst there I asked him to carry out a four wheel laser alignment and, with the car in the air, we discovered some play (gear lash) in the steering rack. I brought the car home and managed to get some adjustment on the rack and pinion. Sorted!

Not sure if the 900 has this rack adjustment but just thought I'd share my experience.

Liam, Many thanks. I'll try the front/rear swap plus balance.

I replaced the steering rack some years ago and my recollection is that there is nothing to adjust on the 940 rack.

The garage owner (years of experience with Volvo and many Volvo contacts to consult with) is apparently off sick, leaving his young but capable mechanic in charge, which is not helping things.

[martin calva]

The garage owner was back today and he called me to come to see what they had found.

My 940 was on a lift with the engine running. The garage owner showed me that, when the engine was revved, with the car in gear, there were strong vibrations to be heard and felt at the centre prop shaft bearing and at the differential housing. It could be the prop shaft or it could be the differential causing the vibration. He was emphatic that this was the cause of the vibration on braking.

He said that his supplier can no longer supply 940 propshafts, so maybe I could find one from a breaker.

This evening I found, via the internet, a breaker within a reasonable distance who has both the prop shaft and the back axle for sale. They are from a petrol 940 saloon (my car is a diesel estate). I am assuming that the propshafts (and the back axle) will be interchangeable between the petrol saloon and the diesel estate. Is that a fair guess?

[360beast]

Originally Posted by martin calva

The garage owner was back today and he called me to come to see what they had found.

My 940 was on a lift with the engine running. The garage owner showed me that, when the engine was revved, with the car in gear, there were strong vibrations to be heard and felt at the centre prop shaft bearing and at the differential housing. It could be the prop shaft or it could be the differential causing the vibration. He was emphatic that this was the cause of the vibration on braking.

He said that his supplier can no longer supply 940 propshafts, so maybe I could find one from a breaker.

This evening I found, via the internet, a breaker within a reasonable distance who has both the prop shaft and the back axle for sale. They are from a petrol 940 saloon (my car is a diesel estate). I am assuming that the propshafts (and the back axle) will be interchangeable between the petrol saloon and the diesel estate. Is that a fair guess?

No you need one for a diesel as the front half will be different, estate and saloon are the same as it is just the bodywork above the saloon boot that is different.

Why not just replace the propshaft bearing if that is worn out? I have tried three different brands PPS, Febi/bilstein and Meyle all with SKF bearings and the only one that didn't fail very quickly and was virtually vibration free is the Meyle one.