Rear Caliper piston stuck: rebuild or replace?

[FutureVentures]

Sooooo, changing the rear brake pads I have discovered the pistons are stuck.

 

Had the rear master cylinder opened and still couldn't push the pistons in, just barely moved.

 

Questions:

-Before rebuilding, what if I try a bigger hammer so to speak, and C-clamp these into position?

 

-How hard is it to rebuild? Will I have to bleed the brake?

 

-Saw used rear calipers on Ebay for $50, no idea if the pistons compress.

 

Other thoughts, ideas? At least it's raining so, I am not missing riding today!

 

Cheers,

[N3FOL]

It could be a case of clogged brake lines that is causing it to be stuck in position. How old are your lines? If you decide to buy a rebuilt caliper, it may be a good idea to bleed and replace all lines at the same time.

[FutureVentures]

It could be a case of clogged brake lines that is causing it to be stuck in position. How old are your lines? If you decide to buy a rebuilt caliper, it may be a good idea to bleed and replace all lines at the same time.

 

From what I read of maintenance, these lines are original.

 

I did attach a bleeder hose to the caliper and opened it a bit, the fluid flowed freely, if that means anything.

[GeorgeS]

Hook back to brake line, Put the two OLD, Pads in place, the use large tool to Fully spread pads, compress the pistons, use pedal to pump them back, then compress them again.

 

Repeat process several times. This might free them.

[saddlebum]

If you do have to rebuild there not bad to do but pull apart and inspect solid parts for pitting and scoring before getting a rebuild kit, if they are then replace caliper

[FutureVentures]

Hook back to brake line, Put the two OLD, Pads in place, the use large tool to Fully spread pads, compress the pistons, use pedal to pump them back, then compress them again.

 

Repeat process several times. This might free them.

 

 

I get the overall idea here, I think, but not exactly sure.

 

"Hook back to brake line"

I didn't disconnect anything, yet...

 

"use large tool"

What large tool?

 

With the master cylinder cover on or off? On, I presume...

[GeorgeS]

OK, OLD pads to push pistons, cause they will be damaged in the process.

 

Somthing to Force the pads agianst the Pistons, to Full Bottom position.

 

Lets say a small crow bar. something to Insert between the TWO pads to force the pads to push IN on the Pistions.

 

Then Slowly pump them back toward center, the force them in again.

 

If the master cylinder fills, when compressing pistions, then you will have to let some fluid out for space.

 

This should lossen up the pistons, and make it eaiser to get them out for clean up and a complete rebuild.

 

How many miles on it> ???? If its never been rebuilt, then it needs a complete rebuild with a new Seal Kit.

[V7Goose]

I have no idea what model of bike you have, but don't jump to conclusion the pistons are stuck.

 

When changing the rear pads on my 05 last year I went my usual route of putting a C-clamp on them to push the pistons back in to make room for the new pads - didn't move! I put enough pressure on the C-clamp to leave circular marks on the finish on the outside of the calipers. Seemed pretty odd to me, since the brakes had been working fine, so I tried to move the pistons by just putting a 1x2 in there and twisting it - they slid right back as they should. I can only surmise that the C-clamp caused them to slightly tip and bind up in the bores. Never had that happen before, and I've done a lot of brakes over the years. Just thought the info might help you take another look.

Goose

[Canuck]

What Vgoose just said. Had the same thing happen just lately after changing the rear tire. Make sure the cups are straight and they should go back in.

[Carbon_One]

Sooooo, changing the rear brake pads I have discovered the pistons are stuck.

 

Had the rear master cylinder opened and still couldn't push the pistons in, just barely moved.

 

Questions:

-Before rebuilding, what if I try a bigger hammer so to speak, and C-clamp these into position?

 

-How hard is it to rebuild? Will I have to bleed the brake?

 

-Saw used rear calipers on Ebay for $50, no idea if the pistons compress.

 

Other thoughts, ideas? At least it's raining so, I am not missing riding today!

 

Cheers,

 

You have a pm

Larry

[FutureVentures]

What Vgoose just said. Had the same thing happen just lately after changing the rear tire. Make sure the cups are straight and they should go back in.

 

Yup, got two of em in last night with a C clamp, but not the other two.

 

Then, when pumping the rear brake, the two that I got to go in, didn't come back out. The two that would not retract, did come out more.

 

Trying to envision how you got a 1x2 in there to pry? Assume it was still on the bike for leverage.

 

I'm going to try again tonight to see if I can get them to move.

 

Thanks!

[KiteSquid]

Also check for foreign material in between the caliper and piston!!!!!! Bikes have a lot more dirt getting at the calipers than cages do....

[V7Goose]

Yup, got two of em in last night with a C clamp, but not the other two.

 

Then, when pumping the rear brake, the two that I got to go in, didn't come back out. The two that would not retract, did come out more.

 

Trying to envision how you got a 1x2 in there to pry? Assume it was still on the bike for leverage.

 

I'm going to try again tonight to see if I can get them to move.

 

Thanks!

My point was that they slid back very easily WITHOUT prying or clamps. When mine did not go right back in with the clamp, I knew they had to be binding up from off-center pressure, so another course of action was needed. I just stuck the piece of wood in between the pistons and twisted it, and the pistons on both sides slid in easily. If you have to put much pressure on them at all, something is WRONG, so stop. The other method I often use is to leave the old pads in place and just stick a large common screwdriver between them and gently twist or flex it to push the pads back (done with the calipers off the bike too). The fluid goes right back into the master cylinder without problem.

 

Think about it - when the brakes are working, just letting off the lever needs to allow the pads to retract slightly and stop dragging on the disks. If any pressure was needed to push the pistons back in, the brakes would just stay tight.

 

Unfortunately, from your description above, I suspect you may have damaged the pistons or bores with the C-clamp. If they were working properly, just a light push on the peddle or lever would cause them to pop all the way out immediately. Good luck finding out what is wrong.

Goose

[FutureVentures]

My point was that they slid back very easily WITHOUT prying or clamps. When mine did not go right back in with the clamp, I knew they had to be binding up from off-center pressure, so another course of action was needed. I just stuck the piece of wood in between the pistons and twisted it, and the pistons on both sides slid in easily. If you have to put much pressure on them at all, something is WRONG, so stop. The other method I often use is to leave the old pads in place and just stick a large common screwdriver between them and gently twist or flex it to push the pads back (done with the calipers off the bike too). The fluid goes right back into the master cylinder without problem.

 

Think about it - when the brakes are working, just letting off the lever needs to allow the pads to retract slightly and stop dragging on the disks. If any pressure was needed to push the pistons back in, the brakes would just stay tight.

 

Unfortunately, from your description above, I suspect you may have damaged the pistons or bores with the C-clamp. If they were working properly, just a light push on the peddle or lever would cause them to pop all the way out immediately. Good luck finding out what is wrong.

Goose

 

First, you and others were bang on about the pistons being twisted, they were. So, I looked closely and could see the pistons were off canter, doh!

 

Applying pressure to the high edge allowed me to get the pistons moving in freely, with just my hands.

 

However, pumping the brake pedal, the pistons do not appear to come out evenly, so I'm thinking there's still an issue.

 

Took the bike for a ride and the rear brake does work fine, but I wonder what bad things are going on...rubbing, over-heating, etc...

 

Carbon One has a spare caliper that I'm going to purchase from him just in case.

[V7Goose]

If you got them to slide with your fingers and they don't leak any fluid when pumped up hard on the bike, all may be OK.

 

I am always careful to NOT apply any pressure to the brake while the pads are out, so I wouldn't know if tilting/binding is normal under that situation. But before I got worried I'd slip a pad in over the pistons and hold it flat against them before I applied a little pressure to the brake - that should ensure the piston stays straight and allow it to operate smoothly.

Goose

[FutureVentures]

If you got them to slide with your fingers and they don't leak any fluid when pumped up hard on the bike, all may be OK.

 

I am always careful to NOT apply any pressure to the brake while the pads are out, so I wouldn't know if tilting/binding is normal under that situation. But before I got worried I'd slip a pad in over the pistons and hold it flat against them before I applied a little pressure to the brake - that should ensure the piston stays straight and allow it to operate smoothly.

Goose

 

Rode the bike the past two days, appears to be working fine. However just to be sure, ordered a spare caliper from Carbon One. Now I can replace and work on mine without losing the precious little riding time remaining in our season.

 

Thanks for all your tips, love this site!

 

Cheers,

 

Erich

[saddlebum]

take it it for a decent ride then after bringing it to an easy stop with the front brake put your hands on the disc if cold or even just a little warm they are ok if hot they are dragging.campare with the other rotors to get a better idea.

[Pasta Burner]

Having a similar issue. A little while back the rear was hanging up, I thought I had it fixed after adjusting the freeplay, then she sat for a month waiting on new tires and me getting time to put them on. Rode to work and home yesterday and the rear was dragging again, I could hear and feel it when trying to push the bike. First as mentioned in another thread I cracked the bleeder to relieve pressure, that did nothing.

second I Took the caliper off last night and externally gave it a good cleaning with brake cleaner and a nylon brush. Two pistons were extended the other side retracted. Using a few clamps and whatnot I individually got all four moving smoothly pumping the pedal and pushing them back in.

put it all back together and rode to work this morning...rotor was hot as hell when I got to work. 5miles.

 

my plan for tonight is to bleed the system and see if that helps. Any other ideas? The front left seems fine.

[BlueSky]

Time for a rebuild I think.

[Condor]

 

my plan for tonight is to bleed the system and see if that helps. Any other ideas? The front left seems fine.

 

Behind the plastic right angle fitting in the line that comes from the rear reserve and feeds the master there's a expansion hole that may be plugged up. It's a very small hole and using a wire tie from the grocery section of your local market is small enough to clean it out. Just strip the cover off the tie. What happens is as the fluid heats up from the pad dragging it expands and puts more pressure on the pads.. instead of returning to the reserve..and the caliper gets hotter and the fluid expands more.. A vicious cycle.... Ride it around town long enough and the rear locks up tighter than a frogs a$$ If you find it's a plugged hole it's time to bleed the brakes... All of them...