Caliper piston wont go back in.

[Guest]

Pretty simple question,

Im trying to get my front wheel back on after getting a new tire mounted. and while trying to compress the front caliper piston so that i can get it onto the rotor it wont go back in!

Pulling the brake lever pushes the piston out nice and smoothly but while using my big ol' C-clamp and Hulk'in out on the thing, nothing... just a sore hand...

Is there a trick to these calipers or is something else wrong with my Lemon-bike?

[JTGS850GL]

Try opening up the bleeder and then compressing it. If it does return then you may have an issue upstream. How old are those brake hoses?

[Bustedknuckles]

Try opening up the bleeder and then compressing it. If it does return then you may have an issue upstream. How old are those brake hoses?

Good idea, and no clue...

[bbjumper]

When was the last tome you overhauled the M/C and caliper?

[Bustedknuckles]

When was the last tome you overhauled the M/C and caliper?

well I just bought the bike 2 weeks ago so never. BUT, JTGS850GL's idea worked. I got the caliper back on and the wheel mounted. Looks like I need to rebuild the MC then...

[boggart]

Useing a G clamp and a socket inside the piston ususally works well.

[TooManyToys]

well I just bought the bike 2 weeks ago so never. BUT, JTGS850GL's idea worked. I got the caliper back on and the wheel mounted. Looks like I need to rebuild the MC then...

You either have the compensating port clogged or if there is a lever adjustment it is set so the master piston will not fully return.

[Nessism]

First of all you need to take the lid off the master cylinder, and make sure there is room in the master for more fluid since you will be pushing it backwards.

A full system tear down and clean out, and replacing the rubber lines, should be considered mandatory for a 30+ year old bike. It's amazing how much crud builds up over the years. If the crud fouls the return port in the master it can lock up the brakes and dump you on the road. Not good. A little maintenance goes a long way here.

[chuck hahn]

I am gonna go with the seal is seized to the piston. What causes this is the groove the seal sit in inside the caliper body gets full of corrosion....thick white calcified looking stuff.

As the corrosion builds it ( of course ) has to displace something..and that something is the seal. Thus the seal gets tighter and tighter against the piston and eventually its seized solid.

My suggestion is to pop out the piston, not only to service the caliper correctly, but to also see that there isnt rusted pitting around the piston where the seal sits. And I would STRONGLY suggest you service the master cylinders and all the other calipers as well. Riding is fun until you need a handful of brake and its not there....OR its there so hard and sudden that a lock up occurs and throws you anyway.

[Bustedknuckles]

Thanks fella's, I will order up some new lines and tear everything down and do a nice little cleanup/rebuild!

[chuck hahn]

Get a nut pick for getting into the very corners of the seal grooves. Some carb spray and a dremel wire wheel works well for the flatter areas. Go easy with it though..lightly brush off the crud till its clean. Too much can make divits and get thing out of round.

[GSX1000E]

First of all you need to take the lid off the master cylinder, and make sure there is room in the master for more fluid since you will be pushing it backwards.

That is absolutely the WORST POSSIBLE thing to do!!!! (Note my sig-line about free advice)
Never, ever back-flush the minerals/moisture that has settled to the lowest points in the brake system INTO the master cylinder!!!!!!! Sure fire way to ruin a working system!
Use a line-lock to stop the flow to the master while opening the bleeders (that you have already drilled the rust out of so that they flow like new) and then retract the pistons back into there bores while the dirty/garbage old fluid
is expelled form the system.

[Bustedknuckles]

I'm going to tear down the brakes and go through them 100% the fact that the return valve in the MC is clogged makes me un-easy about the whole system. This is a cheap beater-bike but one thing I will NEVER half-ass or cheap out on is brakes. especially on a motorcycle... I like my face just the way it is...

[chuck hahn]

GSX..in this case its OBVIOUS that the entire system needs dismantled, cleaned, and bad parts replaced..so if he did back flow anything its of no conciquence.

[tkent02]

I'm going to tear down the brakes and go through them 100% the fact that the return valve in the MC is clogged makes me un-easy about the whole system. This is a cheap beater-bike but one thing I will NEVER half-ass or cheap out on is brakes. especially on a motorcycle... I like my face just the way it is...

They need to be cleaned out inside, front brakes locking up out if the blue is a bad thing. It doesn't take very much rust to block that port, it's tiny. Clean it all from the caliper to the master, new lines, good to go another 30 years.
At least it will be if you change out the fluid every year like you are supposed to.