front caliper

[oldyam80sg]

I looked in the links section but have a couple questions regarding my front brake caliper-right side.With the caliper removed from the bike and cleaned of all fluid,should i be able to by hand- push the piston inwards?or will this be difficult?The reason i asked this is because there is rust on the top of the piston where it pushes the pad against the disc.Is that OK?I looked at the piston and it looked to be in decent shape-no marks on it.When i tried to push the piston back into the caliper it wont go easily.The o-ring that is in the caliper -can that be replaced?What is the best way to get the piston to move inwards?The area the piston goes into is clean of rust.Can i use some sort of lubrication on the inside?

[Rasputin]

If you have the piston out of the caliper, you can use a pick and remove the O-ring. There is usually a build up of gunk behind that O-ring which makes it hard to move the piston. Once you have the O-ring out you can clean the groove it sits in. New O-rings are available and com in the rebuild kits. I got mine from georgefix on ebay. You can use some very fine emery paper or sandpaper to clean any rust etc off of the piston as well. I found the piston hard to push in when i did it until I used a swipe of brake fluid for lubrication and then it went in smoothly. Hope some of this helps.

[oldyam80sg]

I removed the o-ring and there was junk underneath.Once i clean that up should the piston move freely inside the caliper?

[prometheus578]

Let's see...
Yeah, it may be a little difficult to push the piston back in. Not really difficult, but there will be some slight resistance.
You're dealing with a machined fit, sort of. Very close tolerances... not much wall to wall clearance.
And that rubber, square-sided, O-ring gasket doesn't make things easier.
But yes, you should be able to push the piston back in.. though it will be difficult to pull back out again.
This is as it should be.
I usually take a real fine grit sandpaper and polish up the piston and the caliper bore. Piston should slide pretty nicely(with the O-ring removed)
Never had to replace the O-ring. Never saw one go bad (Just don't clean or soak them in Brakleen... they swell up and are then useless!)
Clean the dried gunk offa the o ring... just scraping it with your thumb nail is fine. Anything harder(sharper) and you could gouge it and it won't seal.
Don't forget to take an angled pointy thing and clean out the groove that the O-ring fits into. Calipers hang when the dried out brake fluid behind that O ring builds up and pushes the O-ring tighter into the piston.
No lubricants... just brake fluid. (lubricants may not be chemically compatable with brake fluid.)
Don't worry about the rust on the piston where it meets the pad.

[Rasputin]

Fairly freely. With a little brake fluid on it mine went in with a one finger touch after enough of it was past the oring. It cant be too hard to push in or your brakes would not release.

[oldyam80sg]

I will try that tomorrow.That was my problem as the brakes would not release.

[DGXSER]

Oldyam,

I had the same issue when I got my XS. front brakes grabbed and it was hard to even move the bike until it was riden a a few miles then they worked ok until they cooled back off. Then tight again. I cleaned the spooge hole in the master, and pulled both fronts off and apart (one at atime) used the same o-rings and seals that are most likely original to the bike. Cleaned that groove very carefully and completely, and used brake fluid to lubricate just as the others have suggested (possibly the same guys who told me how to do mine as well). Plenty of gunk in there on mine. Slid back together nicely once you get the bottom lip of the piston over the o-ring.

One other item, is the bolt that holds the caliper on the Special models. Mine was just ever so slightly bent in the threaded area. Replaced it as well. That seemed to make alot of difference too.

Work like brand new brakes.

[theduke]

having the opposite trouble as yam, need to remove my pistons to clean the rust out and change the o-ring, but can't get them out. don't want to do any damage, and wont come out with pumping of the brakes. any advice without doing damage??

[oldyam80sg]

Surprisingly there was no rust behind the piston as i first thought.I thought that because of the rust the piston wont come out.I have a pair of rubber jawed pliers that i gave a slight twist to and held the caliper and hit it with a plastic mallet.I also soaked the caliper piston in penetrating fluid.

[prometheus578]

Answer for The Duke:

Three old threads concerning removing brake caliper pistons, and rebuilding calipers, in general.




http://www.xs11.com/forum/showthread...compressed+air

http://www.xs11.com/forum/showthread...sed+air&page=2

http://www.xs11.com/forum/showthread...compressed+air

[DGXSER]

Duke,

Not the qualified mechanic that some are for sure, but it seems odd that your master can't create the needed pressure to pop it out. Did you keep the master full of fluid as you pumped, not create an air pocket in the line?

If you have access to an air compressor, and I used that technique on my rear because I did not keep the fluid filled and lost the prime on it (don't do that on the rear MC for sure, what a PITA to get primed and bled). Just use the pressure regulator to keep the pressure down when you use that to pop it out. Only use the force required kind of idea. Mine did not ocme out violently, but there was enough crap behind it to make me cringe.

[oldyam80sg]

Today i took the caliper and lightly sanded the inside where the piston goes and took a toothpick and scrapped out the old dried brake fluid behind the o-ring.I lubed up the o-ring with brake fluid and installed the piston.It would not go in so i took a flat screwdriver and lightly scrapped the dried fluid off of the groove.Cleaned groove real good and installed o-ring again.Once the piston got past the o-ring groove it went in easy.Inserted tip of blow gun and using 10 psi was able to blow piston out.Piston again went back in.I only used 10 psi and that was enough to push the piston out.Any more than that and i think that it could break a bone if you don't move your hand.

[bikerphil]

caliper

Sounds like you got it straightened out. Don't forget to clean the cr ap out of the bleeder screw holes.

[oldyam80sg]

Will do.Thanks.Do i really need to put that boot on that covers the piston area?Are they available?Mine has seen better days.

[bikerphil]

boot

Yeah, you can get 'em if you order the caliper rebuild kit. I've fixed 'em before with some RTV black. All the boot does is keep the brake dust out. Fluid will never touch it and it won't be visible when it's on the bike.