MrLexse

I'm changing the pads / dampers on the rear of my S4 and while installing the dampers in each piston, I am trying to envision how they effect brake squeal, but can't. Can anyone explain ?

WallyP

Brake squeal is caused by stick/slip of the pads against the rotor causing the pads to vibrate at an audible rate. The vibration can be damped by putting a rubbery material between the backing plate of the pads and the caliper pistons, by putting a slippery sheet between the backing plate and the pistons, or by bonding small devices to the backing plates that then snugly fit into the pistons. That is the most expensive method, so that is what we have on the 928...

UKKid35

OJ GTS

Imagine that the vibration that creates the sound is caused by the pad moving up and down with the rotation of the disc, rather than in and out with the movement of the piston

928mac

Pull the pads out and rough them up with sand paper.
If the rotor is glazed, sand the shinny finnish off of it.

MrLexse

Thanks. Now I can visualize how it works. What are my options if I choose to go the "slippery sheet " or "rubbery sheet" in order to make pad change easier.

atb

I've used the product that Paul shows above with good results. Bottom line though, some pads are just going to make noise no matter what you do, make sure you start with a pad that is known to be quiet first.

okbarnett

Clean and sand the back metal side of the pads and the round piston then spray Permatex brake quiet on the pad back and let it dry for an hour or so then put it togather and dont scrape the spray off as you do it. I never had any noise

dr bob

The pistons back off slightly when the pedal is released, thanks to the shape of the seals in the caliper. The factory pieces stick the pad hard to the piston, so the pad is also drawn back clear of the rotor. No contact, no casual glazing, and of course no squeal.

The alternative options shared by others work in various ways to dampen the vibrations in the pad that are audible, but none actually pulls the pads back as the caliper pistons and their seals relax. Most common disk brake systems depend on a certain amount of runout in the disc to bounce the pads back clear of the friction surfaces for at least partial relief. You get into a situation where a pad that's tight in the caliper doesn't bounce back easily, while one that's got a little clearance at the edges will be noisy since it can easily vibrate.

FWIW, the last (and only...) time I put pads in my S4, I bought all the new anti-squeal pads but didn't install them. Instead, I decided on a whim to try gluing the old pieces to the new pads with hi-temp RTV adhesive. Figured that I could replace them if it didn't work. But it did, at least for my casual driving with no 'glowing rotors' events. With 55k on the replacement pads it's getting close to needing a new set. I'll get a chance to do a full inspection and evaluation of the durability of the orange RTV. If the old pieces have suffered, of course I still have a full set of now NOS pieces to put in.