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Replacing brake piston seals. Waste of time?


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#1 awacs

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Posted 16 June 2012 - 02:31 PM

Hey VFR gearheads. I've always replaced the brake piston seals on my bikes every few years. Just a prophylactic measure, not that I've had any issues. Is it a waste of time? I ask, because I *hate* bleeding the linked brakes on my 5th gen. Much prefer chasing the old fluid out with new, but that's not an option after disassembly.

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Aram

#2 MBrane

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Posted 16 June 2012 - 03:12 PM

I replaced all the rubber parts in the calipers, and MCs when I installed my new lines around 30K. The seals that came out were noticeably worn. I'll probably do 'em again around 100K or so.

Bleeding the lines is the worst part of the job. Think I'll make myself a pressure bleeder before I do that again.

#3 timmythecop

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Posted 16 June 2012 - 03:27 PM

it is also so important to polish the outer walls of the pistons. If they still have the ridge on em, they muck up the seals on the first squeeze.

Can I convince you to paint it flat black?

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#4 KevCarver

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Posted 16 June 2012 - 04:04 PM

it is also so important to polish the outer walls of the pistons. If they still have the ridge on em, they muck up the seals on the first squeeze.

^^^^
+1
Every time I buy a used bike I go through the calipers and generally the seals are fine. I just clean 'em and the pistons and re-assemble. But that's the same bleeding job either way.
I'd think if you cleaned the pistons in the caliper at every pad change you'd be ok.
By the way, the pistons are pretty long. Without the pads installed they really won't come out, but maybe enough to let out fluid. If you left one pad in and extended the pistons, you'd never pop them out.

Kevin


#5 Lee 2002

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Posted 16 June 2012 - 04:06 PM

Based on my (somewhat extensive work related) experience with hydraulics, the chances of a catastrophic failure are nil. You will develop weeping and dampness long before you have a leak big enough to cause a noticeable loss of braking power. At that point it would be advisable to change seals.

In my opinion, your prophylactic replacement of seals every few years is gaining you nothing more that a lighter checkbook and some peace of mind (which may have some value to you that justifies the practice).



The best thing you can do for your seals is to thoroughly clean the exposed part of the piston before shoving it back inside the caliper when changing pads.
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#6 awacs

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Posted 16 June 2012 - 04:07 PM

By the way, the pistons are pretty long. Without the pads installed they really won't come out, but maybe enough to let out fluid. If you left one pad in and extended the pistons, you'd never pop them out.


Yeah, I've thought about what I think you're suggesting --- pop the pistons out far enough to clean the affected surface, without removing them entirely? I was always too chicken though!

#7 MBrane

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Posted 16 June 2012 - 08:29 PM

it is also so important to polish the outer walls of the pistons. If they still have the ridge on em, they muck up the seals on the first squeeze.


After a simple cleaning the pistons on my girl looked like new. The seals weren't scored, but were noticeably deformed compared to the new ones. I always clean the pistons off before pushing them in when changing pads.

#8 awacs

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Posted 16 June 2012 - 09:42 PM


it is also so important to polish the outer walls of the pistons. If they still have the ridge on em, they muck up the seals on the first squeeze.


After a simple cleaning the pistons on my girl looked like new. The seals weren't scored, but were noticeably deformed compared to the new ones. I always clean the pistons off before pushing them in when changing pads.

What do you clean them with?

#9 KevCarver

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Posted 16 June 2012 - 09:44 PM

Brake cleaner, or some general degreaser.

Kevin


#10 awacs

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Posted 16 June 2012 - 09:46 PM

Brake cleaner, or some general degreaser.


Thanks. That's what I've always used as well.




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