Front brake caliper leaks after seal replacement
Thread Starter
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Intermediate
Joined: Feb 2022
Posts: 45
Likes: 19
From: OH
Front brake caliper leaks after seal replacement
I was cleaning up the caliper and decided to update the seal. Bought a kit and thoroughly cleaned the piston and bore. After seal lubed and installed, it drips with very little pressure. I pulled it apart and verified the seal was not torn or twisted but it still drips.
This is one of the simplest designs I have seen. Not much to screw up so it seems it should be so simple.
Anyone else have this and figure it out? Either the seal is too small? Or the piston has an issue I don't see. It looks fine.
Thanks!
This is one of the simplest designs I have seen. Not much to screw up so it seems it should be so simple.
Anyone else have this and figure it out? Either the seal is too small? Or the piston has an issue I don't see. It looks fine.
Thanks!
Thread Starter
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Intermediate
Joined: Feb 2022
Posts: 45
Likes: 19
From: OH
I couldn't pull it out with my fingers when I took it back apart but that could be because the system was closed and it meant drawing a vacuum.
I suspect the O-ring but it is brand new from Dennis Kirk.
I wonder what the piston to bore clearance should be. Or what the bore diameter and tolerance is? I hate to buy a piston and new seal if the bore is shot.
I suspect the O-ring but it is brand new from Dennis Kirk.
I wonder what the piston to bore clearance should be. Or what the bore diameter and tolerance is? I hate to buy a piston and new seal if the bore is shot.
Stellar HDF Member
Joined: Apr 2016
Posts: 3,331
Likes: 2,122
From: Masshole
It doesn't really seal in the bore itself, the oring fit's in a groove and is stationary. Are you sure you didn't miss or have one of the smaller o-rings move that seal the halves of the cailper together? It could be leaking from those and running down along the piston making it look like those are leaking.
Grand HDF Member
Joined: Sep 2009
Posts: 4,558
Likes: 1,847
From: Albuquerque, NM
Did you verify that the fluid is coming out from around the pistons? There is also the fluid passage from one side of the caliper to the other. That also seals with an o-ring. I knew someone who reassembled his caliper and accidentally left that o-ring out.
Thread Starter
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Intermediate
Joined: Feb 2022
Posts: 45
Likes: 19
From: OH
I am leaning towards it being a seal issue. I did not split the caliper halves so not the o-rings.
It did not leak before I replaced the seal. But is was very grubby and in need of a good clean so used brake clean and a shop towel to clean the bore, seal and boot grooves.
It did not leak before I replaced the seal. But is was very grubby and in need of a good clean so used brake clean and a shop towel to clean the bore, seal and boot grooves.
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HDF Community Team
Joined: Aug 2018
Posts: 3,087
Likes: 1,246
From: New Hampsha
These things are pretty simple. If the piston surface is not pitted then the most likely problem is one of the seals got pinched on assembly.
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Thread Starter
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Intermediate
Joined: Feb 2022
Posts: 45
Likes: 19
From: OH
Turned out to be a bad piston seal. I stopped at the dealership and bought just the seal. it was stiffer than the replacement by a little bit. Installed easily and seals perfectly. Brakes bled out quickly and lever is very stiff.
