Rear brake calipper

I have a problem that rear brake calipper  , not release fully…

Examples:
1. verify the rear wheel spin freely before start driving.

2. after a while I feel it hang more and more.

3. stops the wheel it look at the calipper is super hoot….

4. cool it down with water and the brake release.

no more issue on the same trip…
next time same issue….

One time I feel it was hanging more and more I had bad time and was pushing brake many times, and suddnley it was releasing…


These is happens without using the rear brake….


any ideas?


thank you

You may not have good fluid flow through the holes in your master cylinder.  You will have to flush the system and ensure the holes are clean.

The caliper piston slides over a seal on the inside of the cylinder.  If dirt builds up behind the seal (in the groove where it fits) the piston will be tight.  To check it you will have to pull the caliper off and remove the piston.

The equalizing port (the small of the two ports) of your Master Cylinder is plugged.  When the port gets plugged, excess fluid (due to piston retraction and heat expansion) can't flow back into the MC, which causes the pad to drag, which causes even more heat, causing more dragging, causing even more heat ...... until the brakes eventually lock up.  Use a guitar string to clean the port out and flush with new fluid.

Thank you!

everything was 100 cleaned 3 years ago….

will umount master cylinder.

wrote:

 

Thank you, will check these also, these can be the case, that the pedal is not fully "back", but how is the pressure building up since I`m not using the brake? vibration from driving?

 

I had trouble with my back brake building up pressure to where I had to pull over and bleed the caliper to release the pressure,
so I took it to the local (trusted) bike shop and the owner gave it to some kid to fix.
Fresh pads and a master cylinder rebuild later it was still hanging up, so after two or three  trips back to the shop the owner decided to have a look, he started at the foot pedal and then looked at the adjustment bolt and found the problem.
That was 40 years ago and cost a bunch of time and money but was a lesson well learned.

I’ve never watched my rear pedal, but I bet on a bumpy road it could get pulled up or down adding a slight amount of pressure each bump. Just a guess. I have to believe as mentioned it’s either the adjustments or the pressure relief port that is blocked. 

 

I will check the reelfe valve.

the strange thing is these typicaly happens after 10 min, and after that I can run for many hours without any issues….

It has never happend twise on the same day trip…. Only in the start of it.

Following this topic.

Having the same problem on my gpz11 uni rear brake.

New master cylinder and rebuild kit. New brake line. Rebuilt caliper with new seals and new piston. Relief valve not blocked.

Starts off fine then brake drags after about 10 mins and seizes solid until it cools down.

Just in the process of stripping it down and rebleeding to see if that makes a difference.

probably aligment