Low Speed Brake Vibration 1996 850, 190,000Km

[valvster]

Cheers from sunny Sth Australia....
Newbie to this board and first post
I have a weird braking problem that has shown up in the last few weeks that is intermittent and seems to be dependant on air temperature.
Car has new discs front & rear with genuine Volvo pads to rear and Polytech pads at front fitted July 2007.
Discs show no signs of warping...no high speed vibration when applying brakes going down a long steep hill.

Brakes work perfectly at stopping the car smoothly & quietly but just before coming to a halt (less than 5kph) there is vibration of the whole front of the car, including the steering wheel, similar to chalk across a blackboard but without the squeal.

When braking the engine revs do not drop below idle & Gbox in N does not cure problem.

Releasing the brakes and then applying again would sometimes result in an
end to vibration & a smooth stop.

Problem is often intermittent but mostly with gentle application of brakes
when coming to a stop but only during the last 5 kph.

Problem appeared during every stop on Mon & Tues whilst air temp was high 37

[farupp]

This is a strange problem and I do not know exactly what it could be. With the car up in the air such that the front wheels can turn freely, spin the wheels or rotors to see if you are able to observe even the slightest warpage of the rotors. While looking, see if the front pads are glazed in any way, or if there is any pad compound deposited on the rotor itself.

With new pads and rotors it is important to bed them in properly when you first put the car back on the road. It is possible that this wasn't accomplished successfully, and there is, as a result, slight warpage or glazing.

By the way, what is a "broken bitumen?" I don't think we have those in South Carolina, USA, but we do have other strange things!

Good luck, Valvster.

[MadeInJapan]

Since you have no vibration at high speeds, I'm with the other poster that it could be glazing of the pads and/or compound on the disks. Do as he says and get a closer look. The compound or even "hot spots" on one of the rotors would make sense because as the temperature decreases and with higher speeds it would be less noticeable. If it's the pads glazing, you could get a mechanic to gently skim a layer of the compound off and it will cure it.

To bed the brakes properly, after a pad change, get the car up to highway speeds and slam on the brakes going to a complete stop. Drive, allowing the brakes to cool without braking and then repeat the above 4 or 5 times. This heats and cools the pad compound and matches it up with the rotors preventing future pad-to-rotor issues.

Good luck and keep us posted!

[valvster]

Thanks for the reply guys....
The mechanic reported very slight glazing but not enough to warrant skimming the rotors.
They have used this brand of pads for years and never have any problem with them however I did have the car back to them after a couple of months because the inner pads were rattling in the calipers, they put some more goo on back of the pads and the problem disappeared.
The rattle has gradually reappeared but the mechanic reports the goo is still doing its stuff. The car has had no suspension repairs to it so I'm wondering if the rattle and brake problem are caused by worn control arm bushes or even the links on the end of the anti-roll bar.
With the extremely high temperatures from braking I don't understand how
10-20deg C variation in air temp can have such an effect on the pads.
Hopefully we will get 30deg C days next week and I can replicate the problem with the mechanic in the car.
Oh and broken bitumen....I guess you call it tarmac or hardtop? A lot of our roads around hear are patched upon patch so are not particularly smooth.

cheers....Valvster

[valvster]

Problem Fixed....I removed the rear pads on both wheels and everything looked OK except the left rear inner pad backing plate had a nice round impression in the centre of the plate/shim where the piston makes contact plus another overlapping impression as well, almost as though the piston was coming out of the caliper at an angle.
Both pads had little wear on them and there was no blueing of the disc so I pushed the piston squarely back in to the caliper and swapped the pads and shims (cutout shims) around, so far no problems even on 30degC days.
This is the first time I have had cutout shims on the car and have to wonder if they have contributed to the problem.
cheers....Valvster

[Brucebo]

[quote="valvster"]Cheers from sunny Sth Australia....
Newbie to this board and first post
I have a weird braking problem that has shown up in the last few weeks that is intermittent and seems to be dependant on air temperature.
Car has new discs front & rear with genuine Volvo pads to rear and Polytech pads at front fitted July 2007.
Discs show no signs of warping...no high speed vibration when applying brakes going down a long steep hill.

Brakes work perfectly at stopping the car smoothly & quietly but just before coming to a halt (less than 5kph) there is vibration of the whole front of the car, including the steering wheel, similar to chalk across a blackboard but without the squeal.

When braking the engine revs do not drop below idle & Gbox in N does not cure problem.

Releasing the brakes and then applying again would sometimes result in an
end to vibration & a smooth stop.

Problem is often intermittent but mostly with gentle application of brakes
when coming to a stop but only during the last 5 kph.

Problem appeared during every stop on Mon & Tues whilst air temp was high 37

[valvster]

Hi Bruce....my problem has totally disappeared since my last post, I suspect if you have a whole of car vibration and can't feel it in the steering wheel have a look at the rear brakes as the source of the problem.
In my case I now think the problem was caused by incorrect installation of the left outer rear pad....I suspect one of the guide pins did not pass through the pad and allowed it to swing on the other pin.
I have no idea why the ambient temperature was a factor in the problem.
It is an easy job to swap rear pads around so give it a try.

regards.....Valvster

[Brucebo]

Hi Bruce....my problem has totally disappeared since my last post, I suspect if you have a whole of car vibration and can't feel it in the steering wheel have a look at the rear brakes as the source of the problem.
In my case I now think the problem was caused by incorrect installation of the left outer rear pad....I suspect one of the guide pins did not pass through the pad and allowed it to swing on the other pin.
I have no idea why the ambient temperature was a factor in the problem.
It is an easy job to swap rear pads around so give it a try.

regards.....Valvster

Yes it was the rear brakes. Both sets of pads were down below minimum and the caliper cylinders were fully extended. I installed new pads and shims and that fixed the problem. I recently bought this car and the breaks were squealing. I started with replacing the front pads and that's when the problem showed up, so I spent the last two weeks chasing ghosts as well as changing rotors and pads. I guess changing the front pads changed the braking dynamics enought to change the braking load on the back brakes causing the problem to appear!

-Bruce

[baldjohn]

Did anyone also have ABS and TRACS error lights too?

My shutter problem also happens more often when it is really hot, but it feel to me as if the ABS is trying to pump the brakes. I guess I will take it to my Volvo guy and have him take a look at the rotors.

I'm wondering what the noise sounds like to the cars next to me!?