Michael posted to the list:
The Person I bought my (89) 928 S4 from said that the reason brakes squeal is that the pad is so hard, and that that was just something they did.
Personally I have never heard of such a thing but the car seemed to be in good shape otherwise. I had the wheels off the other day and there's plenty of pad left. My question is this typical for 928's or has someone else experienced the same problems. Pleas reply to my personal email address if you can offer any help. Michael
Hard glazed pads will often squeal. Glazing is sometimes the result of too much slow driving, but more often occurs when the pads drag on the rotors all the time. As some others have mentioned, brake dust sometimes contributes even on cars where the pads retract adequately when the pedal is up. Others also mentioned the anti-squeal goodies that hold the pads to the caliper pistons, and the RTV-style goop that you can buy to glue the pads to the pistons. I'll add to that, and mention that a very light resurfacing of the rotors may be necessary to break a glaze on them too.
Not yet mentioned is sticking calipers, or calipers where the rubber boot has been damaged. The piston is actually retracted by the resiliency of the piston seals. They roll out a little when the brake is applied and the piston is pushed out, then roll back when pressure is removed, thus pulling the piston (and the pad) back slightly. If the dust boot is damaged, dirt and brake dust may keep the piston from sliding back completely. It also might allow water to get in the gap between the caliper and the piston, promoting corrosion.
On a lark, I decided to try to reuse the anti-squeal clips that stick to the backs of the pads. I'd purchased a new set, but decided to try the old ones anyway. So the new pads went in (Axxis Metal Masters) with the old parts, with a dab of Hi-Temp orange RTV gasket maker on the face of the clips. New, they have a peel-off pad that exposes some adhesive. I stripped that stuff off the old ones (very easy) and just put a dab of orange RTV there, then dropped the new pads in. So far, at maybe 15k on the 'new' brakes, everything is fine. Might be the different non-original pads, might be the glue and the anti-squeal clips. The Metal Masters from 928 Specialists came with a happiness guarantee, by the way, and so far I'm very happy.
If I could just perfect the technique of getting those pad wear sensors out without cracking the plastic...
There have been a few posts lately regarding brake squeal and what to do to stop it. After the track day at Hallet, OK during the 928 OC convention, I decided I needed new brake pads before driving home. I had Mo put them on at his shop where he graciously worked me into his hectic convention schedule.
Mo used Metal Master pads and used a material made by BG Products to prevent squeal. It is a thin low viscosity liquid, and the mechanic just put a few drops over the entire surface of each pad and let it soak in for a while. It went on the friction material side of the pad, not the backing. The brakes were assembled without the usual round anti-squeal disks. Just pad against the piston. No beveling of the pad edge or any other technique.
It works fine. I have had the pads on for about 6000 miles now including one track day at Thunderhill where the brakes got very hot. I have never heard any offensive sound from them hot or cold.
The product is "Stop Squeal" by BG Products, Wichita, KS., 67213. I bought a small container (1 fl oz) of the product from Mo.
BG Products had a presentation of their products at the convention. Possibly Marc White could obtain more info on contacting the company if anyone is interested.
Yep, Louie. The stuff works. It has been amazing me for about 6 years now.
If anyone wants info about this, please contact the company at 316-265-2686. Mailing address is 701 S Wichita, Wichita, KS 67213.
Subject:  Squealing Brakes
On my '87 S-4, the front brakes are squealing badly. I just had the rotors turned today. The pads are less than 50% worn. Any suggestions on what to look for?
1987 Porsche 928S-4 Guards Red (Weekend Car)
1987 Porsche 928S-4 Venetian Blue (Daily Driver)
1982 Porsche 928 Pacific Blue Metallic (Sold, Wrecked by New Owner)
1977 911S (Metallic Blue, In Restoration)
On the Aluminum Brembo Calipers (S4 onwards for definite not sure about
earlier) the most likely cause is corrosion of the Alu caliper behind the
stainless anti rattle clips on the leading and trailing edges of the steel brake
pad back plate. A good time to completely clean and repaint the calipers. - The
corrosion can be quite deep (like 1/8")
The corrosion expanding forces the anti rattle plate against the pad causing the pad to skew slightly which makes the squeal when you break gently.
Black SE - No brake squeaks and currently no clutch.
Brake noise is basically vibration. Common knowledge on the subject is that
if you put some sort of damper between the end of the piston and the back of the
pad it will keep the vibration from hitting the annoying frequencies. These can
be actually silicone pads that you install, grease or stuff that is like a caulk
that dries after you paint it on.
The pads and the stuff that dries go bad after a while. Especially if you are a DE person or a hard driver. I use a synthetic blue goo caliper assembly paste. Really high temperature and sticky stuff that doesn't break down at brake temps as far as I can tell. That is in about two years because all my brakes come off all my cars every two years. On my winter car that is because of back roads... On my 928 it is either because of maintenance or because I warped the rotors :)
The most tame street pads are the quietest. The most racy pads are the loudest squealers. Lots of pad wear especially uneven and no cleaning will make for some noise even with anti squeal pads in place because the dust (metal) gets in between the pad and piston and makes a solid joint canceling the dampening effect. So many just get the hose out and clean the brakes out every year and that can help.
I had this phenomena: when the car was used for a longer stretch, let's say 1 hour, the right front brake started to squeal. High pitched beep which happens only at about 50 km/h and can be influenced by turning the steering a bit or pressing the brakes gently. For a long time I thought it was due to wear of the disk and I might solve it by shaving off the edge of the pads a little, or maybe due to corrosion the pad did not move freely and gets stuck. Early 2016 I decided to have a good look and resolve this.
Guess what? The vibration dampers that are supposed to keep the pad hooked up to the pistons were nicely in place, stacked to a thin metal plate ... that was supposed to be glued against the brake pad itself. It had separated and the pad was now in free flow. That caused the issue !!
I used high temp RTV to glue the plate back on and let it cure for a day. Since then the brake was silent again.