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Brake Piston Seals


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Rebuilding my front brake calipers and getting ready to reassemble, do you recommend using some kind of lube on the seals or just brake fluid ???

 

My searching on the internet has been inconclusive, lots of people recommend using Castrol Red Rubber grease, which is water resistant and DOT 4 compatible, but apparently not sold in the USA, and none of the specific brake lubes sold here in the US mention DOT 3 / 4 / 5.1 compatibility on their label's or data sheets. Service manuals don't seem to say anything on the subject, but small packets of lube are included in a number of caliper rebuild kits, I believe Brembo sends it out with their rebuild kits.

 

 

 

 

Tyler

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Do not mix brake fluid types, e.g. 3 vs 4 vs 5.1

 

When I have cleaned my brakes, I have always used a brake grease like the red Castrol you mention for the seals. But having it available also makes it a bit easier to do so.

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While I have used wheel bearing grease ( a light swipe with a finger) on cars I have never used anything but DOT 3-4 to assemble pistons. I do not like DOT 5 because it isn't hydoscopic, there is no problem mixing DOT 3 or 4 and in fact most say DOT 3/4. Other than a few properties you always have to keep in mind all petroleum products came from the same place and will mix back together.

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DOT 3,4,Super 4, 4 Plus, and 5.1 I believe are all the same basic thing with differing boiling points, Better Living Through Science and all that. Dot 5 is a silicone based fluid that is hydrophobic and shouldn't be mixed with any other kind of brake fluid, and is not recommended for "performance" situations.

 

My understanding of using grease on the brake seals is that it cannot cause the rubber seals to swell, thus petroleum based greases are not recommended. It also needs to dissolve into the brake fluid so as not to clog any of the little passageways inside the caliper itself. Withstand the extreme heat that brakes generate without breaking down and possibly contaminating the braking surfaces themselves.

 

From what I've read the advantage of using the correct grease on the seals over just brake fluid is that it creates a hydrophobic barrier on the seal preventing contamination of the fluid and corrosion or damage to the inside of the piston. and makes installation of the pistons easier.

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  • 2 weeks later...

I have always just used brake fluid on the seals and pistons during install, has never failed me and assembly has always been easy. So I don't feel one needs the grease but having never used it maybe it is better?

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You can use just brake fluid but if you can get rubber grease then it greatly prolongs the time between caliper rebuilds due to road salt etc., by which I mean corrosion. For about 15 years I never used it but I have some now and went through the last two winters no trouble. I think it's castor oil based but I'm not too sure. Don't use silicone grease, i have seen several bikes where they have ended up suffering from the pistons not being well gripped by the seals, and sucking back into the calipers, so giving way too much travel at the lever. You do only need a smear, could you ask someone at a race meet for a little? A teaspoon will last you until you're old and grey.

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