Brake vibration/ noise problem

[dan_b]

Have a new problem with my front brakes, need some help!

I've got the Porsche (Brembo) 968CS 4-pot calipers. They're not the monoblock jobbies.

Recently replaced pads with Ferodos, and last week, replaced the anti-squeal shiims for new ones, as was getting pretty nasty brake squeal at low braking pressure, from the right caliper.

Brake squeal cured. But, on the car's first long journey since putting in the new shims (return trip to Cambridge), a HORRIBLE noise/vibration has surfaced.

Every few minutes or so on the motorway, a fairly high frequency noise would start up, which would increase in volume and intensity until you actually start feeling some vibration through the car. Only way to cure it was to apply a tiny bit of brake pedal. Of course you can't drive down the motorway with your foot on the brake the whole time. Step harder on the brakes and it goes away for a minute or two, only to come back.

Interestingly, on my way back from Cambridge it started raining very hard, and the problem disappeared.

What's going on? Is it something to do with the pad retaining mechanism? The pads were very difficult to get in when I replaced them - perhaps the pad isn't fully retracting when you come off the pedal? Why is it doing it now with the new anti-squeal shims? Why did it stop when it started raining?

It's awful. What can I do?

[williams]

Hi,

Had similar problemb with my set up and found it to be the pad guide pins on the calipers were touching the discs after the had warmed up and expanded. I removed a couple of mil from the pins and the noise has now gone. Check the discs for scoring. Are you using 30mm thick discs?

Alun.

[Pete_RS2]

I had the same problem a few months ago. I too fitted new anti-squeal shims and cleaned the calipers thoroughly including the stainless steel pad guide plates. The pads were still tight so I ended up grinding a bit off the edge of the pads to make them fit better. No problems since.

[dan_b]

I'm using 30mm discs (should be 32mm for the correct Porsche installation), which have been on the car since January and it's had about 7000miles of pretty vigorous braking since. The pads have been on for about 2 months, like I said this problem wasn't occurring until I put the new anti-squeal shims on on Friday. Discs look clean and smooth.

[audiman]

The pads should fit into the caliper with ease. What your are getting is the brake binding on slightly, causing the noise. Peters solution above is pretty good, thats what i would do. The pads must be free to move in the caliper.

[dan_b]

I did give the calipers a right good blast with brake cleaner and a liberal application of Copslip, but it's clearly fouling something.
That does sound like my problem, and a solution therein. What did you use to grind the pad backing down with? I'm a bit short of grinding equipment.

[Pete_RS2]

I had access to a mini DA. You may be able to use a Dremel or something similar ?

[dan_b]

Don't even have a Dremel

[dan_b]

Incidentally, putting in the new anti-squeal shims has solved my intermittent ABS gremlin issue, which was a bonus.

[Alistair E]

I had the same symptons on my Avant with what I was told were Porsche 928 calipers. Mine had a tendency for corrosion to build up under the stainless steel pad guides. This resulted in the guides no longer being sprung and tightening on the pad. It was strange that it was fine just after fitting new pads and cleaning under the guides, but would re-appear when the pads had worn down by about two thirds. It was particularly evident after a few back to back heavy stops.
The only possible reason I could think of was that the pad backing plate became hotter quicker due to the thinner pad material. I am not convinced by this argument but it was the only reason I could think of at the time.
Eventually got fed up with the noise. Boxster S monoblocs, no problems so far.

Alistair

[dan_b]

I don't really want to have to change my calipers just yet, only had them on the car 10 months! And, if I did change them, I'd only want to upgrade again...

I'll have a go at grinding off the edges of the pads a little. It seems it's a bit of a crummy design - I presume the later monoblock calipers have a different pad retaining system?

[audiman]

just use a file or similar. Alistair, that sounds a very plausable theory.

[dan_b]

I'll pop them out on Thursday and use a spare emery board from my wife's manicure set, I'm sure she won't mind

[Mikes2]

This is caused by plate lift on these calipers. Very common as moisture gets between the plate and the caliper body.

You can file the edges of the pad backing plates to ease fitting of them but this should be considered a temporary measure.

You can buy replacement plates from Audi but the hard part is removing the retaining bolts for the plates.

[dan_b]

Hi Mike
Did you experience this issue on your car? Did you do the pad filing trick?