Member
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Join Date: Jan 2012
Location: LA
Posts: 179
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Member
Join Date: Jan 2012
Location: LA
Posts: 179
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The OE pistons are not just polished steel, they are chrome plated. They have excellent corrosion resistance. The issue is that moisture collects around where the boot fits to the casting...then slowly creeps under the boot and around into the bore where as the paint or zinc plating degrades, pinching the piston...as seen in your picture.
The problem becomes worse in rebuilt caliper because the surface where the boot fits is no longer a clean machined surface, but a blasted more porous surface...so the boot doesn't seal as well as it once did.
Once the caliper is all cleaned up and re-assembled, pull the boot back and squirt it full of silicone dielectric grease...then burp the air out until grease oozes out of it. Once it's full of grease, it won't get able to get full of anything else and it will live considerably longer.
This is not a toyota specific problem.
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