928S4 Brakes Replacement question
Chronic Tool Dropper
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Joined: Oct 2001
Posts: 20,506
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From: Bend, Oregon
Thank you all for the help. Got it done last night. Cracking the bleeder was the ticket. Calipers look great, and all 8 pistons compressed fully and smoothly. She is all back together with fresh hardware. Re-used the pad backers(dampers). They were in good shape. Bled it out. Great pedal, but really doesnt stop any better. It was pretty good to begin with. I had one pad, on one side, that was making noise for some unknown reason, and it was hellaciously embarassing when rolling up next to hot babes at the stop light. Under inspection of both the rotors and pads, nothing too much out of the ordinary. Not sure where the noise was originating, but the noise is now gone, and I feel better with having those old, dirty pads off of it.
Thank you all, and thanks to Roger for some phone support.
Thank you all, and thanks to Roger for some phone support.
Pads are "noisy" when they either don't fit tight enough between the steel plates (rumble) or when they vibrate while dragging on the rotor (squeak or squeal). The 'dampers' when new have an adhesive face that sticks to the back of the pads. Meanwhile, the pistons ride in square-section seals in the bores. When applied, the brake pistons cause those rings to roll slightly. On release, the slightly-rolled rings draw the piston back a few thousandths as they move back to their relaxed condition. Drawing the pads back just a few thousanths is all that's needed to avoid the squeaking noise, and the glazing and heating that often result from dragging the pads on the rotor.
Some folks use anti-squeal products on the rear of the pad to dampen vibrations against the pistons, That takes care of the noise but leaves the glazing and heat.
Conclusions: It's easy to avoid buying the dampers and either put pads in bare or use one of the blue-goo products. But for the relatively few dollars they cost, the dampers do more than the goo will. If you are really tight, you can clean the old ones and re-glue them to the new pads. You may end up doing that a few times in the life of the pads though, as I did on the last set of pads.
On the steel guide/wear plates, they should be cleaned carefully. Old brake crud/dust/whatever can get behind those plates and cause them to be too tight on the pads. But it can be a major chore to get the screws out with the caliper assembled, so do as much cleaning as you can aand see if you can get the pads to go in without disassembly. The pads should just fit between the plates with zero clearance. I usually put a film of waterproof synthetic grease on those plates where the pad backing plate contacts.
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Can you tell I just rebuilt the calipers and replaced pads recently? Gotta share this stuff while I still remember it...
Thread Starter
Racer
Joined: Nov 2011
Posts: 309
Likes: 33
From: St. Augustine, Florida
Pads are "noisy" when they either don't fit tight enough between the steel plates (rumble) or when they vibrate while dragging on the rotor (squeak or squeal). The 'dampers' when new have an adhesive face that sticks to the back of the pads. Meanwhile, the pistons ride in square-section seals in the bores. When applied, the brake pistons cause those rings to roll slightly. On release, the slightly-rolled rings draw the piston back a few thousandths as they move back to their relaxed condition. Drawing the pads back just a few thousanths is all that's needed to avoid the squeaking noise, and the glazing and heating that often result from dragging the pads on the rotor.
Some folks use anti-squeal products on the rear of the pad to dampen vibrations against the pistons, That takes care of the noise but leaves the glazing and heat.
Conclusions: It's easy to avoid buying the dampers and either put pads in bare or use one of the blue-goo products. But for the relatively few dollars they cost, the dampers do more than the goo will. If you are really tight, you can clean the old ones and re-glue them to the new pads. You may end up doing that a few times in the life of the pads though, as I did on the last set of pads.
On the steel guide/wear plates, they should be cleaned carefully. Old brake crud/dust/whatever can get behind those plates and cause them to be too tight on the pads. But it can be a major chore to get the screws out with the caliper assembled, so do as much cleaning as you can aand see if you can get the pads to go in without disassembly. The pads should just fit between the plates with zero clearance. I usually put a film of waterproof synthetic grease on those plates where the pad backing plate contacts.
----
Can you tell I just rebuilt the calipers and replaced pads recently? Gotta share this stuff while I still remember it...
Some folks use anti-squeal products on the rear of the pad to dampen vibrations against the pistons, That takes care of the noise but leaves the glazing and heat.
Conclusions: It's easy to avoid buying the dampers and either put pads in bare or use one of the blue-goo products. But for the relatively few dollars they cost, the dampers do more than the goo will. If you are really tight, you can clean the old ones and re-glue them to the new pads. You may end up doing that a few times in the life of the pads though, as I did on the last set of pads.
On the steel guide/wear plates, they should be cleaned carefully. Old brake crud/dust/whatever can get behind those plates and cause them to be too tight on the pads. But it can be a major chore to get the screws out with the caliper assembled, so do as much cleaning as you can aand see if you can get the pads to go in without disassembly. The pads should just fit between the plates with zero clearance. I usually put a film of waterproof synthetic grease on those plates where the pad backing plate contacts.
----
Can you tell I just rebuilt the calipers and replaced pads recently? Gotta share this stuff while I still remember it...
I utilized the old "dampers", by cleaning the backs up and using a thin film of Permatex, per Roger. Worked fine. New pads quieted the brake noise right down, and hopefully get rid of the brake dust.
