Brakes squealing, help!

[scphelps1]

Well, I finally thought I was getting close! After about 2 months without being able to drive the car I finally had all the parts and bolted the calipers back up. I will give a quick rundown of what has been done; new strut assemblies, new front wheel bearings, new front rotors, hats, pads, and rebuilt calipers. Also flushed fluid with ATE Blue with a piece of a 2x4 under the pedal so it wouldn't go too far.

I bolted the calipers up on Sat and went for a brief ride, being pretty cautious. I stepped on the brakes hard a couple of times, but I'm not sure of the best method for breaking in new rotors, pads. Doing so caused the steering wheel to go back and forth and a high pitched squealing from the front brakes. The sound is reminiscent of warning squealers, for pads so equipped, only LOUDER. This was a brief ride, and when I returned home the front rotors were pretty warm.

Today I decided to have another go at it. I started on the passenger's side and the pads came out fairly easily. I hadn't lubed the backs or sides with any caliper grease, so I decided to give that a shot. I'm not sure if that's usually recommended, but I figured it couldn't hurt. The driver's side inboard pad was fairly tight to get out, so I decided that this might be sticking and part of my problem. I ground some more off the backing plate so it would fit a little looser in case it was sticking when I released the brake. No luck. The driver's side is still squealing. Any ideas?

I went with Porsche pads because of what I've read about other pads squealing, and yet these are squealing anyway! I even tried to chamfer the leading edge, as I've heard sometimes that can cause a problem; all to no avail! I question if they are the right ones because of how much material I had to take off of each backing plate for them to fit. Perhaps someone can check this number: 964.351.930.03.

Any insight would be greatly appreciated!

Oh yeah, anyone want to buy a 930, really cheap?!?!?

[scphelps1]

Bump for the Mon AM crowd. I did some reading this morning and noticed that several others have heard squealing to this embarrassingly high level. So, has anyone been able to get to the root of the problem?

BTW I replaced the rear pads on the AWD Volvo over the weekend. Pads and flush with ATE in about an hour and no sqealing. I thought the older ones were supposed to be easier to work on!

[Jeff]

Clayton, did you index the caliper pistons to 20 degrees of the rotor surface?

[scphelps1]

The calipers were rebuilt by VCI, so I assume they did it correctly. Also, does this apply to the 930 calipers? I've read the tech article before, but I believe the subject was an SC. I know the difference between the calipers, but I'm not sure of the indexing for the pistons.

[Jdub]

Yes, it is critical that the cutout on the caliper puck face the oncoming rotor, that is why the template for the 20degree (use Search if confused here...).

Sadly, Porsche brakes squeal. At least mine do, and I was very good about getting it all right on the caliper rebuild. It may be you have a slightly stuck puck -- that might account for it.

I guess you would have to inspect the calipers directly. This means removing them or getting a very clear look in at the pucks and making sure the cutout faces the rotor. If you had to move them (rotational -- in the caliper body) I believe you can without removing the seal, but my memory is foggy here...

John

EDIT: There is no need to grind any part of the pad, front or back, to accommodate the puck's ability to move in and out: the pucks are supposed to handle any latitude needed to push the pads out and then pull them back in again. Note that the "cross" metal piece, held in place against the pads by the two pins, is supposed to not only keep the pads in place but also help move them away from the rotor. You might take a hard look at those, though making them work any better after countless heat cycles is not a possibility. New ones might be in order?

[Wil Ferch]

I could be wrong but I don't think the 20 degree caliper indexing applies to 4 puck type calipers like 930's.

The 4-puck caliper types will always tend to squeel more than the 2-puck calipers.

Try a combination of this:
- file a small , 45 degree edge all 4 sides of the brake pad material.
- put a high temp grease on the outside-edge of the backing plate...especially those surfaces that make contact berween the pads' edges and the receiving-bore of the caliper.
- on the pads' backside, use a 3M acrylic aluminum anti-rattle self stick material made for this purpose.

I think you need to do all three for any chance of success.

---Wil Ferch