911LE

To answer one of the OP's other questions, shims are interchangable between aftermarket and OEM. The steel backing that the pad material is bonded to is the same no matter who manufactured the pads. Buy cheap aftermarket shims if you need them as they are just stamped steel.

Johnhav430

This tech explains the OE shims, are for OE pads. Don't need them when using aftermarket because as many of us know, Akebono already has shims on all their pads, not just Toyota products. But he suggests saving them, for when you do want to use OE pads.

Solid is outer, slotted is inner. Even Prius have them. 8 per axle, 16 per vehicle. Obviously many of them get thrown out, so if they are not used, it's not the end of the world.

911LE

Or just use "liquid shim in a bottle"

It fits 100% of pads on the market with just one part number!

Johnhav430

Not to derail the thread, but my BMW has semi metallic pads, and when they have about 15-20k on the rears, the car will make a "squeak squeak squeak" sound. This was when the cars were barely 1 1/2 yrs. old, people would say it's so embarrassing, makes my car feel and seem cheap. Guys on the forum all had this issue, and they started saying only way to fix is to get new pads (why when they are only 1/3 worn if that?). I took my car to the dealer under warranty, and noise is not covered beyond the 12k adjustment warranty, even on a BMW.

So what the dealer does is warranty work billed internally--remove pads, clean carriers, and they put some of that on all the pads, as I saw when I did the brakes myself. Didn't work or help. So I wanted to test whether just new pads got rid of that sound--they did. The unfortunate reality is that if one cannot live with the squeak, they had to get new pads prematurely. The car mfgs. put a lot of research into frequencies, groans vs. squeals, pad to rotor, pad to piston, etc. Long story short is this is a first world problem, there are countries in the world where tires are changed without a machine and using one's feet and fire.

911LE

Does your BMW have floating calipers? It's a totally different design than the LS's fixed caliper design. Floating calipers, which most cars use, have more areas that noise can start. If I do brakes on a floater I pull the bracket and all the pins/slides and clean everything. Regrease the pins and make sure the dust boots are installed correctly and seated. The caliper installed without pads should slide easily on the fresh grease and will ensure even pad wear. I then use the high temp grease on the back of the pad or shim where it contacts the piston (inboard side) and the caliper housing (outboard). I've done 100's of brake jobs and never had a noise issue. Some pads, like older GM's, must then be staked to the caliper with a large flat head screwdriver and a hammer.

Most brake noise comes from clearances in the system. If the pad isn't always under at least a little pressure it can rattle or knock. This is more important on fixed caliper designs as the shim is the only thing there to take up the slack. If it's properly installed it acts as a slight spring to keep the pad in contact with the rotor at all times. No rotor is perfectly flat so when you release the brakes and drive the rotor slightly pushes the pads away. As long as there is a shim there to take up the slack no noise is produced. Shims themselves can be loose on the pad and create noise as well. That's why I slightly bend the tabs on the shims inward before I install them on the pad to insure the are tight.

Johnhav430

excellent points! Yes, my BMW has floating calipers (wish they were fixed)...the BMW dealer used a yellow pad quiet so when I changed my brakes, I saw them on all 8 pads....factory is gray.

That's why my indie advised me to put the shims in the fronts where he duplicated that knock sound by tapping on the eyelets if you will of the front LS pads, where the pins go through. He thinks with shims, there's no sound...

imho floating calipers are inherently prone to uneven wear, and it's so easy for the inner pad to wear more than the outer. Someday when I grow up, I want 6 or more pistons in the front brakes, and at least 4 in the rear...

911LE

Floating calipers don't wear pads unevenly if they are installed correctly. Most shops just put pads in and don't address the "floating" aspect, mostly due to not understanding how they work. Theoretically they should be better because they should be equalizing pressure on each side. Fixed calipers can't do that and rely on hydraulic pressure being equal on both sides. This works great in theory but in reality water contaminated fluid and/or air in the system wreaks havoc. Any bit of air in the caliper will compress and absorb pressure and braking force won't be equal on each side of the caliper. Race cars use fixed calipers because there are less moving parts and they are a stronger design which equates to less flex and more stopping power. Pads and fluid are changed after every race so they don't care about uneven wear.