rear brake problem

[gilou]

hi , i need your help , my rear brake make me crazy ;
first question; my fj 1100 has 2 piston in the rear caliper ( 1984 ), and my dealer says it' s strange because we only see one piston on part list .
what about you ? is it original build ?
second question the pistons don't return after braking
i have check 3 time the master cylinder , very clean and all the small holes are clean , the seals are in good condition.
the 2 piston of the caliper were cleaned and had receved new seals.
stange phenomena , after braking the pistons don't come even i open the small bleeder screw !
i had try with new or old brake pads , it' the same
in the operating cycle it' s the seals witch allow the return of the piston i think , so i am ready to put the old seals ??
did you had this problem?
thanks for your help

[andyb]

Rear brake locks on solid after use, even after releasing pressure at the screw?

They're binding somehow.  Pads sticking, getting cockeyed or such?

Stock wheel?  If you're using a thinner brake disc than spec, the pads can in theory get hung up on the caliper rather than return.

Quickest way to check that I can think of would be to install new pads (more thicker because of newness).  To do same for cheaper and faster still, use a piece of shim stock type materieal (aluminum or steel or whatever, a few cut up beer cans would work).  Stick between pad and rotor.  Use brake firmly until pads seat completely in garage, then see if wheel can be rotated and shims fall out.  Sorta making the pads thicker and changing where in the piston travel it's seeing pressure.  If they fall out easily, then your pistons are overextending themselves somehow, most likely due to worn pads.

Also usual ideas apply.  Check for a burr or nick that could catch on the pad and prevent it from returning.  Strikes me that the failure is mechanical rather than part of the fluid system if everything else checks out properly.

[gilou]

hi andib the wheel and brake disc are stock , i tried whith new pads ;same problem i had cleaned and check all the parts properly!!
i'm going crazy
i did the same work on the front wheel , the only difference whas original parts yamaha for the rear brake and adaptable parts for the front!
the front is working very very well !

[racerrad8]

If the bypass/return port in the master cylinder is blocked then the caliper will maintain pressure until you release it.

I would check the master cylinder and make sure both holes a completely open when the lever is released. I have heard of some aftermarket parts not allowing the piston to fully return to open.

I believe this was experienced by axiom-r on his conversion as well.

Randy - RPM

[RichBaker]

An old, original hose can collapse internally and cause the same problem.....

[andyb]

If the bypass/return port in the master cylinder is blocked then the caliper will maintain pressure until you release it.

Absolutely, I've fought that before also.  But releasing pressure at the bleed nipple should allow things to retract normally (on the caliper side).  The master will screw it right back up as soon as you use it again, of course.

[gilou]

hi , after many hours i've find the solution
there were two problems
first one the two hole to bleed in the caliper were not machining at the same place !! it seemed incredible but when the piston was
totaly pushed in the caliper (with the new pads) it was very difficult to bleed properly the system. i took the dremel and enlarge the hole


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after that it was very easy to bleed the system
second problem
in fact the brake was working very well , it was only the caliper witch was not aligned with the disc !!!!
after came loose the caliper bolts , there was no problem !! i understand now why the old pads were slant wear .
i have just now to align the caliper and it will be ok