Why wont rear caliper piston release

[mjpxs11sh]

hey all, still working on my smokin rear caliper. i pulled and tested the rear caliper off the caliper bracket and found the pressure is not totally releasing off the piston. its hanging up causing the disc to heat up while riding. as soon as i open the bleeder it will obviously let the piston go back in, so whatever causes the pressure to be released is the problem. i just had taken the whole rear system off and cleaned the MC and spooge hole with the reservoir off and blew out the MC, lines, and caliper with compressed air. appreciate any assistance

[bikerphil]

The m/c plunger rod may be adjusted too tightly causing the brake to not fully release, JAT.

[BA80]

If the spooge and the hoses are ok, that's the only other thing that it could be.

Back off the adjustment on the push rod.

[mjpxs11sh]

ill recheck. i remember someone here posted a space of 7mm, and thats exactly where mine was, but its probably a matter of function and not nec. a measurement. how about the MC spring? anybody had issues with that? i think its the only other part thats in play with relieving the pressure. anyone that experienced sticky rear brakes? seems to be common after sitting 4 yrs

[BA80]

Yeah, but it's usually an issue with a stuck caliper piston or clogged spooge.

If the MC piston cup doesn't retreat back behind the spooge when realeased then the brake fluid can't return to the reservoir through the spooge and release the brake.

You do realize that there are 2 holes in the bottom of the reservoir right? The feed hole, which is comparably large and can be readily seen, and the spooge hole which is further forward and VERY small and at the center af a small indent. Much more difficult to see and clean.

Not trying to insult, just asking.

[mjpxs11sh]

yes, i used a wire tie to clean it on the bench, it didnt seem to be clogged. then used compressed air to blow out all rear brake components. i didnt have snap ring pliers though, so i didnt take the MC piston out. the system seems pretty basic, but im suspicious of the MC since its the only part i didnt disassemble. still not sure though! thanx 4 ur response!

[DGXSER]

If you did not pull the MC apart, there could and most likely is a bunch of gunk inside there. That gunk could easily have plugged the spooge hole up. You really need to pull that thing apart and clean out the insides of it. The rear MC just takes normal snap ring pliers you can get cheap enough at Harbor Freight. Its the front MC that takes the looonnngg nose snap ring pliers.

[mjpxs11sh]

thanx DGXSER

yeah, thats what ill do. are there any issues to watch for when reinstalling piston and seals? i read somewhere here someone had a problem when they put theirs back together after rebuild. something bout the seal, plunger?

[DGXSER]

It is a major PITA to bleed the rear system. As to the plunger, that tends to be more of an issue with the front mc if you squeeze the handle clean back to the bars. As to bleeding the rear system...mityvac.

[mjpxs11sh]

yeah, ur correct. still hardly a pedal aft constant bleeding. left overnite and ck'd this am. maybe ill put the new pads on i bought, but reinstalled the old pads cause the caliper was sticking. pulled the MC apart, cleaned all internals, but no problem found. like i said, now i hardly have a pedal.

[jurgenkoppen]

Bleeding the rear

I have gone though all this. If you are sure the spooge hole is clean, the easiest way to get the pedal to come back is to suck in more brake fluid through the rear bleeder screw. I put a clear hose, about 6"long, filled with brake fluid fit tightly on the nipple. Then , as you bleed the system press brake lever, release nipple (with the fluid filled hose attached on nipple above your wrench): The air gets ex-spelled via bubbles through the fluid in the hose. On the brake release leave the nipple open, so you suck the now air- free fluid back into the caliper. Then close nipple, refill clear nipple-hose with fluid and repeat.
I find that this cuts out on a lot of time pushing fluid and air from the reservoir. Lemme know if this works for you....Cheers, J

[DAVINCI]

It is a major PITA to bleed the rear system. As to the plunger, that tends to be more of an issue with the front mc if you squeeze the handle clean back to the bars. As to bleeding the rear system...mityvac.

+1 on the Mityvac...before i bought one, tried everything including bleeding with the system off the bike, then re-installing. Yikes. With the mityvac it's a breeze.

[crazy steve]

Another vote for the Mityvac; I wouldn't even bother trying any other method now.

It makes bleeding the rear in particular a snap; the front is a bit tougher. I bled the front and rear on the SG a couple of weeks ago, and starting with dead-empty systems I had both bled in under an hour, with most of that time devoted to the fronts. I find that you can't quite get all of the air out of the front (unless you 'reverse bleed' by forcing the fluid in at the calipers, but that's a bit messy and has a harder set-up), but you'll get enough out that by just letting bike sit overnight, the rest will rise to the master and give you a firm lever the next day.

The trick with a Mityvac is getting a good seal at the bleeder. It will suck air past the bleeder screw threads most times, making you think you still have air in there and slowing how quickly it works. I always wrap about 2-3 turns of teflon tape on the bleeder screw threads, this makes it go much better....

[mjpxs11sh]

thanx Jurgen

i initially sucked on the caliper banjo till i got the fluid. yeah, tastes terrible but didnt care. still spongy and no bubbles comin out! ill try ur method and see what happens. took the MC apart to clean, but was ok. this sucks. i want to ride

[Phoenix Rider]

If you haven't already done this. here is just another thought. When you took apart the caliper did you remove the rubber o ring seal? The o ring is tapered. Sometimes what happens is the fluid crystalizes and collects under the edge of the rubber o ring pushing up against the piston not allowing it to retract. I had this happen to my fronts. They can be clened up with a very fine copper wire wheel with a Dremel at a low speed. The wheel will not score the inside of the caliper, but will clean out the o ring channel nicely.

Good luck,
Wayne