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Dotetcher

Rear caliper won’t release.

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 So after replacing the header I took the black bird out for a ride and about halfway into the ride noticed that something didn’t feel right from the rear end. Not mine. The bikes. So while I was moving I pulled the clutch in and just coasted to a stop and noticed that the rear caliper wasn’t releasing the disk.  At first I thought the caliper was binding but after getting home and releasing the pressure from the banjo connections at the brake pedal it seemed as though the caliper freed up quite a bit. So is there a valve or a small passageway for the brake fluid that could be obstructed in someway shape or form.

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I have read about other bikes with this exact symptom. I believe there was a pressure relieve passage in the master, very small, that could be obstructed and lead to pressure build up in the rear caliper. 

  Have you regularly replaced your brake fluid?

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There is no valve in the master.  There is the port that lets fluid in/out of the cylinder.  Did you recently adjust the pedal height or remove the master, or make any changes in that area?  The piston isn't returning far enough back to uncover that port, usually happens when someone makes a pedal height adjustment, or maybe the pedal or piston is sticking.

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it could be the slider pin is gummed up.years ago the one on mine was full of crud.it has a 14mm bolt head. i recently replaced front and rear brake pads and the rears were sticking with the new pads.slider bolt was clean so gave the pistons a clean by pushing them almost all the way out and cleaning them with a rag dipped in brake fluid.made no difference so ended up refitting a half worn set  and that was enough to bypass the problem.am interested in hearing others responses to your question as im stumped where to look next to fix them. 

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The check valve slapper references would be in the secondary master cylinder, and that can become clogged. 

 

Differential diagnosis would include finding what piston(s) of the rear caliper are hanging up.

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14 hours ago, Dotetcher said:

 So after replacing the header

I would be looking at any other part that was touched during the header swap.  I think the right muffler attaches to the right peg bracket, maybe something there got moved/tweaked.  Maybe a hose got pinched.  At least 90% of the time that a new problem arrises right after fixing something it was an effect of the repair process.

 

And I forgot about the LBS.  Grab a wrench that fits the banjos on the caliper.  Ride 'till it starts to tighten up.  See which has pressure, now you'll know which circuit has the problem.

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Found this link that explains how the linked brakes work. http://ixxra.org/birdbrakes.htm 

Sitting on the bike in the driveway while i have the rear caliper released I grab a handful of front brake and release. According to the link the two outer pistons of both are activated while engaging the front brake. When I release the front brake the bike rolls freely. Did this a number of times with the same result. Engaged the rear brake pedal, then released and the caliper is locked. So I'm thinking its either the center piston binding or problem somewhere in the rear circuit. Back to work.

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Released pressure on rear most banjo. Caliper still engaged. Release pressure on front banjo. Bike rolls freely. Back to it after it cools off outside.

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The front brake will only apply rear brake when in motion so grabbing front brake sitting still would do nothing to the rear.  There's a master cylinder attached to the left front brake, braking force pushes on that master to apply rear brake.

 

Regardless, there appears to be a problem with the rear brake pedal/master cylinder.  Do the test again, when it's locked up pull up on the rear brake pedal and see if it releases.

 

How long did the bike sit before getting the new header on and going for a ride?

 

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Which banjo on the front released the pressure, and are the front brakes binding at all?

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21 hours ago, Dotetcher said:

loosening the forward banjo on the rear caliper releases the rear brake. Front brakes are fine.

 

Sorry, I misunderstood your earlier post about releasing the front brake. If the rear is sticking and the front isn’t, my money is on a problem either in the rear caliper or between it and the rear master. If it was the rear master itself, the fronts would drag as well. 

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Sitting here in my underwear is when I do my best thinking.  Trouble is, that thinking isn't backed up by fact because I can't just run outside and look.

 

Soooo........

 

Front banjo of rear caliper should run to the proportioning valve, and if you trace the line on the other side of the proportioning valve, it should end at the......secondary master cylinder, located on the left fork leg.  The secondary master cylinder can get gunked up and not release pressure.  And PCV's have been known to go bad as well. 

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This place is on the verge of becoming a Jeep forum.

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8 hours ago, superhawk996 said:

This place is on the verge of becoming a Jeep forum.

 

No shit.

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8 hours ago, blackhawkxx said:

Not for all of us.

 

Yeah, for the rest of us it's a gun forum. ;)

 

 

Bill, when you going to sack up and buy that .40 from me? :P

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So back into the rear caliper issue. Bike hasnt moved since the last time I posted about the problem. Went to move it to a better position in the driveway and the bike rolled fine. Hit the rear brake a couple of times and the problem returned. Loosened the banjo at the proportioning control valve and the caliper released. Retightened. Hit the rear brake a number of times. No problem. Took the bike for a spin. No problem. Loosened and retightened both connections to the PCV while applying a little pressure to the rear brake. Just enough to dribble a smidge of brake fluid. Retightened. So far things seem to be ok. Gonna take it for a spin this evening (carrying the appropriate tools) and see what happens. Maybe some smegma in the valve that cleared itself? 

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Anything's possible.  Sometimes stuff just hangs up for no apparent reason then 'fixes' itself.  If it's been a while it would be a good idea to do a fluid flush.

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9 hours ago, superhawk996 said:

Anything's possible.  Sometimes stuff just hangs up for no apparent reason then 'fixes' itself.  If it's been a while it would be a good idea to do a fluid flush.

Will do.

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On 7/1/2018 at 8:31 AM, rockmeupto125 said:

Trouble is, that thinking isn't backed up by fact because I can't just run outside and look.

 

Why not?  It can't still be cold out there.

 

 

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