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While there are posts on BrickBoard about caliper rebuilds there is nothing about preparing/cleaning the caliper bores & O-ring recess & pistons. Though its possible to remove light rust and varnish from caliper pistons and bores with 1200 grit abrasive paper, the major deposits of rust and varnish appear to be in the O-ring seats as per photo. Its only "light" rust and varnish - there is no pitting.
I was told at a brake shop that the piston surface and the O-ring seat in the bore must be perfect or they will leak, since they are the sealing surfaces. So how do you clean the O-ring seat without a sand blasting machine?
Abrasive paper will get out some of the deposits, particularly in the center of the seats, but to clean the inner edges would require some sharp object like a scriber run around the seat. The sharp oblect in the photo is a screwdriver with a bent & sharpened point to clean seats. I also used this to dig the seals out. Will this wreck the surface or is some soft (brass) tool needed?
After cleaning up the caliper there seems some confusion about which way to insert the new O-ring. Maybe the O-ring is tapered but looked square to me even with a magnifying glass. One of the red dots in the photo only goes halfway across O-ring - it appears that this small red dot is to face the base of the bore.
If you just say buy remanufactured calipers, this is not so easy or cheap in Australia. I paid a major brake shop $150 per front caliper ($300 for the pair) for "refurbising" - no simple replace seals by them. $300 got caliper split, sand blast, hone bore (if necessary), fit stainless steel sleeve (if necessary)replace piston(s) (at additional $34 per piston if necessary), fit O-rings & boots and paint - yes paint! But only in their color - black! Never again!
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