Squeaking rear end - one cause found!

[kingzetts]

I have had a persistent issue with squeaking from the rear end (no rude comments please!) for years. It would be most prominent at town speeds, had a frequency which was clearly road speed related, and would only appear once the car had warmed up a bit. Gently applying the handbrake would either change the nature of the squeak or cause it to disappear, applying the footbrake would case it to vanish but only whilst the brakes stayed on. I had had it pegged as handbrake related but had never been able to eliminate it.

Recently I found the cause. There were faint witness marks on the "mounting bells" of both rear brake discs about 1cm outboard from the actual flat disc surfaces. The clearance between the inner edges of the brake caliper casting and the disc bell is very tight at that location. What seems to have been happening is that when cold there was a few thou of clearance, so contact was not apparent when investigating on the lift or with the IRS out of the car, but when the brakes (or possibly just the diff assembly) warmed up, the clearance was disappearing and the edges of the calipers were kissing the bell. Applying the brakes was causing just enough outward flex in the caliper to restore clearance and stop the squeak.

I know my calipers are correctly shimmed to sit centrally. So I am guessing that the repro discs I have on the rear may have ever so slightly thicker bells than the originals. I could probably solve the issue by reshimming the calipers to sit slightly more outboard for extra clearance, but the better solution will, I think, be to grind a bit off the corners of the calipers (sadly either option is an IRS-out job).

As a stop gap, I used a powered "finger" belt sander to clean off the casting roughness and surface rust from the disc bells in the relevant area. This did not totally eliminate the noise, but the car had to get a lot warmer before it appeared (after significant braking, or prolonged motorway running) and it disappeared much quicker once ambling along again.

Just thought I'd report this here in case it helps other with the same issue.

[golfnut324]

Great job finding that one John. I would hope that the disk vendor would be interested in passing along to the manufacturer that they need to trim 0.003" off the bell...but maybe not.

Thanks for posting.

[Jeremy]

Masterful. Must have been so satisfying when you diagnosed it. Well done John.

[Maikel]

I should have read this before.

I am just about shimmimg my 61 and 62 rear brake calipers.

The outer caliper half was kissing the dome of the rotors and could not even turn. Hence I had to grind the corner off on both sides to ha e some clearance.

I noticed another thing with these aftermarket rotors.

They need more shimms to align.
The early cars do have the thin rotor and and the calipers with the thin bridge between the pads. There is not much to do wrong.

Only way to get everything straight is to use more shimms.













My rotors are Made in UK, does anyone has better experiences?

Thanks

Maikel