940 Intractable Vibration on Braking Problem

[martin calva]

My 1994 940 Brake 2.4TIC starts to vibrate when braking every few years. Normally, I change the front disks, then no more vibration on braking for a few more years. Calipers and hoses were replaced two years ago.

This time, here is the story to date:

- I changed the front disks and pads - vibration as bad as before.
- I bought a set of Bosch disks - vibration as bad as before (and frighteningly bad if braking hard from motorway speed)
- I bought a gauge micrometer and magnetic attachment. Run-out on front disks well within spec (0.01 mm, 0.02 mm. Haynes says should be less than 0.06mm.)
- I gave the car to a local garage, Volvo specialist. He tried new disks and pads - vibration as bad as before. (Third set of new disks tried)
- Garage disconnected ABS and vacuum pump to servo. Vibration on braking still there.
- Garage found slight play in the front suspension triangle joints, so replaced bushes. Vibration as bad as before.
- Garage found significant run out on RH rear hub. (I skidded on snow 13 years ago and damaged the wheel and Panhard rod on striking the curb.) I obtained a replacement half shaft, fitted by garage. Vibration as bad as before.

That's the story to date. The chief mechanic says he has the impression the vibration is worse when braking from coasting fast in neutral than when in gear. I left it with the chief mechanic that he would consult the garage owner (on holiday at present) by phone as he was out of ideas on what to check.

Any suggestions how to diagnose the problem? Any suggestions what the problem might be? Between the garage and myself we have tried everything that seems worth trying. But obviously we are missing something somewhere. The vibration is not something in the imagination. As I said, when braking from motorway speed, the vibration is very bad.

Martin

[360beast]

Volvo did different length strut rods for the front as vibration when braking was an issue from the factory, It would be worth measuring the length of yours to see which you have. I think it was Baggy that provided the information on what lengths meant what a few years ago.

[classicswede]

Braking under vibration is a common problem but can always be solved

Sticking caliper slider pins
worn TCA bushes - always upgrade to PU or consider them a service item in rubber
worn bottom ball joints
worn steering rack/track rods/tie rods
worn front wheel bearings
worn or loose front dampers

warped disks are low on the list and you have more than covered that already

[360beast]

Originally Posted by classicswede

Braking under vibration is a common problem but can always be solved

Sticking caliper slider pins
worn TCA bushes - always upgrade to PU or consider them a service item in rubber
worn bottom ball joints
worn steering rack/track rods/tie rods
worn front wheel bearings
worn or loose front dampers

warped disks are low on the list and you have more than covered that already

I found the majority of the vibration when braking went away after getting a wheel alignment on mine.

[TonyS9]

Worn front wheel bearing/hub is a difficult to detect problem.

My steering wheel would wobble gently at low speed and nearly rip the steering wheel out of my hands under hard high speed braking. Checking the wheels for movement didn't show up anything, I did all the bushes and joints which helped but didn't eliminate. The only thing that fixed it was new hub, which cost £60-£150 each. The left one was the worst, but the right one needed changed too. This was after about 180K miles.

[martin calva]

Originally Posted by TonyS9

Worn front wheel bearing/hub is a difficult to detect problem.

My steering wheel would wobble gently at low speed and nearly rip the steering wheel out of my hands under hard high speed braking. Checking the wheels for movement didn't show up anything, I did all the bushes and joints which helped but didn't eliminate. The only thing that fixed it was new hub, which cost £60-£150 each. The left one was the worst, but the right one needed changed too. This was after about 180K miles.

Many thanks for that info.

A quick question: Was there any indication that the bearings were knackered (eg noise on rotating the whee)? Is it possible that the bearing retaining nuts had not been adequately tightened?

A thing to discuss with the garage.

[TonyS9]

Originally Posted by martin calva

Many thanks for that info.

A quick question: Was there any indication that the bearings were knackered (eg noise on rotating the whee)? Is it possible that the bearing retaining nuts had not been adequately tightened?

A thing to discuss with the garage.

Normally worn bearings would be detectable when going around corners or movement in the wheel when pushed on the jack. I've had that in the 360 but not the 940.

The bearings and nuts where the original factory tightening, on very tightly, actually difficult to achieve which my tools, but even with slightly lower than spec torque its been fine with new hubs since then.

[360beast]

Originally Posted by 360beast

Volvo did different length strut rods for the front as vibration when braking was an issue from the factory, It would be worth measuring the length of yours to see which you have. I think it was Baggy that provided the information on what lengths meant what a few years ago.

Found them

https://www.ipdusa.com/products/2151...-Volvo-6819079

[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

[martin calva]

Originally Posted by 360beast

Found them

https://www.ipdusa.com/products/2151...-Volvo-6819079

Many thanks. I'll discuss with the garage.