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stuck piston

Posted: Fri Feb 23, 2018 12:10 pm
by kwl82
Trying to rebuild caliper. Seal kit from AR. Followed instructions and watched videos. Went ok but this is as far as i could squeeze in piston. Seems stuck on inner seal? Tried to compress with brake spreader but wont move. Does the inner seal need to be perfectly flush against wall? Mine wasn't. Should I blow it out and try again? any thoughts? Thanks

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Re: stuck piston

Posted: Fri Feb 23, 2018 2:23 pm
by AZRuss124
It doesn't look like the seal is seated properly. It also looks like you are trying to install the piston dry. lube it will some brake fluid.

Re: stuck piston

Posted: Fri Feb 23, 2018 3:09 pm
by andy
I cant see the image (restrictions at work) so Iam assuming this is a front caliper.

But if the inner seal is not fully seated that is a problem. The groove for that seal needs to be free of all corrosion/dirt/sludge.

A narrow flat blade screwdiver with the tip bent 90 degrees makes a great tool for cleaning the groove.

As notes use a little brake fluid as lubricant and you should be able to get it back together with little difficulty.

Re: stuck piston

Posted: Fri Feb 23, 2018 5:25 pm
by kwl82
It is front caliper. I used what seemed to be liberal amount of brake fluid to lubricate. There was fair amount of grime in old groove and I was able to get most out. Likely needs to be removed and cleaned more thoroughly before trying again. also pretty sure the top seal is backwards in the pic. Thanks. I'll try it again

Re: stuck piston

Posted: Fri Feb 23, 2018 7:41 pm
by kwl82
the plot thickens... i blew out the piston twice today. both times the brand new seal was worn/damaged on one side. Dunno what causes that. the worn part is between 10 and 2 in the pic on inner part of seal that touches piston. the piston is smooth all around. Also i cleaned out the inner seat. there was a surprising amount of dirt still in there
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Re: stuck piston

Posted: Fri Feb 23, 2018 9:56 pm
by bartigue
This isn't a seal issue, it is a corrosion issue. Inside the groove where the seal rests you have something causing it to rise up - and any rise is too much. I use a hook pick like a dentist tool to clean out the entire groove repeatedly, then blast out the caliper with brakleen, then blast it out with dry air. I use brake fluid (clean fluid) on the seal and caliper piston. If the piston requires more than hand force then the seal isn't sitting in the groove.

Pistons ride ONLY on the seal, the caliper "bore" is just a chamber. Therefore the quality of the seal and piston are essential. When in doubt, replace with new.

Also put in the outer seal last, after everything else is done and the piston seated.

Re: stuck piston

Posted: Sat Feb 24, 2018 10:50 am
by kwl82
Thanks all for the advice. I sprayed brakleen then used my dremel with soft wire attachment. It fit nicely into the groove. Resprayed with cleaner and wiped out.There was a surprising amount of dirt that came out still. My concern is after doing that I tried to slide the piston into the bore with no seal in (with brake fluid lube) It seems extremely tight. There is next to no wiggle room and it feels as if there is even the slightest seal protruding it will stick again. I have to order another seal set so wont be able to try again until delivered. Btw, does anyone know if the inner seal can be purchased at a local store? I support AR and 95% buy from them but for a simple item like a rubber ring it would be nice to quickly grab locally. Thanks again

Re: stuck piston

Posted: Sun Feb 25, 2018 10:10 am
by bartigue
The fit is snug. If you look at the piston it is designed with a beveled edge so that it is slight smaller when first encountering the seal. I’ll admit I’ve used a thin smear of grease on the piston when installing, which may be a “no no” but it seems to work to no ill effect.

Don’t use just any seal - brake fluid eats everything not specifically made to resist it.

Re: stuck piston

Posted: Fri Mar 02, 2018 2:34 pm
by kwl82
Ok , i think i got it done. scraped, wiped and rinsed inner seal groove with brakeclean until shiny. wet sanded piston a bit with warm soapy water and 2000 grit paper. new seal and used a little sil glide from napa. piston pushed in with moderate finger pressure and tucked in dust seal. think i got it correct. now for the other side :D . many thanks to all and AR for the phone support and quick shipping

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Re: stuck piston

Posted: Fri Mar 02, 2018 7:46 pm
by andy
Looks great! Nice job!