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Fitting Seals To Brake Caliper


beta tim
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I have just tried to re-buid the back brake caliper on a 2004 Rev-3 as the pistons were seized. It now has new pistons and seals but they leak. I have removed the pistons and found small slithers cut from the new seals which has occurred when I fitted the pistons . Can anyone tell me how to fit the pistons without damaging the seals. ( last time I used a silicone grease spray to re-fit them )

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I have just tried to re-buid the back brake caliper on a 2004 Rev-3 as the pistons were seized. It now has new pistons and seals but they leak. I have removed the pistons and found small slithers cut from the new seals which has occurred when I fitted the pistons . Can anyone tell me how to fit the pistons without damaging the seals. ( last time I used a silicone grease spray to re-fit them )

When pushing in the piston, it's quite easy to catch the outer lip on the outer radius of the bore. I usually drop the piston in until the seal lip rests on the beginning of the bore and then use the end of a thin sharp pick inserted carefully between the seal and the bore and move it around slowly to ease the outer lip into the top of the bore, using very little pressure on the piston. If you're uncomfortable using a pick, use a thin piece of 35mm negative strip (hard to find in the digital age now) or if the piston/bore clearance allows, use a strip of the negative film around the piston (don't overlap the ends of the strip) like you would use a piston ring compressor.

The seal lips are sometimes flared out so that they seal better with added pressure on the inside but most are like a band, either way, the inner lip condition is critical.

Jon

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The seals I was sold were like a band and didn't seem to have any kind of a lip, I looked at them for some while trying to decide if they were tapered in some way but they seemed to be a flat band. I need to get some more so I'll ask Lampkins and this time try a bit of 35mm film. Cheers.

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When replacing the seals, take your time and don't force anything.

Why were your original pistons seized, were they corroded or dirty?

When you get your new seals, check very carefully the recess/groove in the caliper that the seal fits in, it must be scrupulously clean or the seals will always be tight on the pistons. Split the caliper and clean the groove out with a thin piece of plastic so you don't damage the aluminium caliper, wash it out with old brake fluid until you're sure its clean.

Lubricate the new seals and pistons with brake fluid, fit the seals making sure they're seated evenly, then slip the pistons in. If they don't go in easily i.e. moderate thumb pressure, something's wrong, either the seals aren't in properly and evenly or the piston is not being inserted squarely.

Don't use mineral or silicon grease as a lubricant. You can buy a red grease compatible with brake fluid & seals but it's hard to track down, I just use lots of brake fluid.

Again, take your time and don't force anything.

Edited by GII
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