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Old 02-09-2020, 08:58 AM   #9
Norm Peterson
Scooby Specialist
Member#: 498642
Join Date: Mar 2019
Chapter/Region: Tri-State
Location: our wrx IS the family sedan
'19 WRX Ltd 6M dgm
'08 Mustang GT (the toy)


Originally Posted by Yeeman19 View Post
Im not sure the shims are necessary.
No, possibly, and be careful.

There's no guarantee that you'll get any noise without them present - or that you won't get any noise if they are.

What they also do is provide a little thermal insulation of the caliper pistons (and the fluid behind them) from the heat generated during braking (the shim being separate from the pad backing plate acts slows the conduction of heat, acting a little like insulation). This is mainly an issue if you track your car, but may be something to consider if you do a lot of driving in the mountains where the braking tends to be more severe than on flat land.

On the 'be careful' part - keep in mind that when you aren't running shims that the caliper pistons are sticking out further (by the thickness of the shim) at any given combination of pad and rotor wear. Mostly this doesn't matter until you get pads and rotors down to min thickness, where you'd have less margin against popping a piston out of its bore. Basically, don't run your pads or rotors all the way down to the specified min thickness; make your discard thickness about a mm thicker than spec if you're not running shims.

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