Hi all.
I changed a front brake caliper a week ago and with that new discs and pads at the front.
I've driven 1000 miles since then but a humming sound has persisted when braking medium to hard or when braking for more than 3-4 seconds. My neighbour drove it and we're both at a loss.
Everything is fine. The discs and not warped and look fine. Pads seems fine as well. It brakes evenly and the sound seems to come from both sides. The sound very clearly changes with speed.
My nieghbour's only suggestion was that that combination of discs and pads just makes that sound.

Pads are genuine Volvo, brand new. Discs were given to me by the previous owner who was a mechanic at a Volvo dealer. They are from Germany but doesn't have a name on them. They've been lying around for a few years but looked fine.

I'm also a bit dissapointed with the Volvo pads. I've always heard they were really quiet but I can sometimes hear them when braking. Like hard pads on a metal disc would sound. Pads were run in carefully and don't squeak or howl.

Any suggestions? I can't live with the humming so if it can't be solved I'd have to buy new discs.

Cheers

You properly described how you installed the pads and rotors... and I assume you properly checked the rotors for glaze or improper surface and cleaned them properly with brake cleaner before installing them, but you failed to mention anything about installing shims between the brake pads and the calipers. Shims are an important part of the braking system used primarly to reduce any noise transmitted up into the car. This noise stems from the pads temporarily attaching to the disk and traveling with it until they hit the caliper and break loose - thousands of times per second, producing various kinds of noises. Shims allow the pad to move without repeating this cycle all the time, quieting the noise. Install hi-temp grease between the pads and the shims, effectively sandwiching the grease so it will not hit the caliper or the rotor.

Good luck, and let us know how it goes!
--
-Flup, 240DL Wagon, 2 subs in the trunk, Dancing Bears Sticker to top it off :)

The discs had been lying in my garage. I cleaned them up, used emery paper and elbow grease and finally brake cleaner.
I used shims and plenty of quality copper grease on both sides of the shims and on the top and bottom of the pad plates. Also greased the pins going through the pads.
Was it wrong to put grease between the shim and pistons? I've always done that in the past.

Cheers

Not necessarily wrong, but certain kinds of grease can eat through the rubber seals around the pistons... i would be careful
--
-Flup, 240DL Wagon, 2 subs in the trunk, Dancing Bears Sticker to top it off :)

As long as they can carry a tune...

It is absolutely definately the brakes. Most likely the discs and I can sometimes feel the vibration a bit in the steering wheel.

Cheers

You say the discs aren't warped - the max runout is only 0.1mm or 4 thou so it needs care to check visually. Also check the thickness of the discs at various points around the circumference (with a micrometer) to ensure the rear surfaces are machined parallel to the front.

Only other suggestion I have not mentioned so far would be check the steering rack for play.

I have experienced the grating sound you mention from genuine Volvo pads. I'm told they have an 'abrasive layer' to condition the surface of the discs when first installed. Personally I won't use them again - having used non Volvo pads for years (on replacement discs) the discs had a near original surface. One set of Volvo pads and they look as if they need to be replaced.

You're right that I probably wouldn't be able to see if they were warped. It just seems unlikely that two new discs are both warped.
And would warped discs actually make a sound? This humming has a frequency of 2-300Hz at around 50mph which sounds to much if was just warped.
A rarely feel the vibration in the steering wheel. Only braking hard passing certain speeds.
Annoying.

Glen: So the grating sound should go away?

Cheers

Warped discs usually cause vibration or 'judder' at lower speeds - ie as you come to a stop. Worn control arm bushings (or tie rod ends) can cause vibration, which might only be evident in your case when the brakes are applied.

It's difficult to say for sure - so these are just suggestions to check.

As for the grating - yes, on mine it disappeared after a while - but so did the disc surfaces!!

Also - I'm always a bit wary of anything that's been inexplicably 'kicking around the workshop for a while'. It can be because the parts were obtained for a refit but rejected because they were out of tolerance.

Just a thought - but I'd be inclined to check prior to fitting (difficult with discs though).

PS If the discs are German they may be Bendix (Honeywell).

Hmmmmm... (pun)

Maybe its the driveshaft center bearing &/or it's support?
These sometimes hum when on their way out.
Since center bearing is in center, the sound is not left or right.

If sound is definitely from front, then probably not from the driveshaft support, as their sound does not appear to be particularly from front or rear.

Re. pads, I've REALLY gotten to like Wagner pads. They have beveled edges & bonded-on shims that do a great job at eliminating squeal.

Surprisingly enough, my very good independent Volvo-specialist mechanic also told me that he prefers them.

- verify the model of Wagner visually, they have various 'grades'.
- - (should have bevel and shim)
- if shim is not centered properly on pad, no problem:
- - - (locking pin holes don't line up), no problem:
- - Shove shim over w/screwdriver blade at shim edge
- - or blade pushed into pin hole.
- Shim will bond with heat under use.