Rear Brake Issue help

[ccsct203]

i'll try it tonight.
Thanks again

Maybe some build-up internally, small bore to clean so I'll have to do the best I can.
Maybe If I just buy one on Ebay....

[mz_rider]

I have rebuilt nearly everything on my my bike.
The issue I'm having is this;
The back brake caliper is dragging on the rotor.
I took the rear caliper was disassembled and that seem fine.
No rust.
I reinstalled the same seals back because they seemed fine
The adjuster is all the way in
could the rear master cylinder be bad?
Could the pressure applied to the caliper not be releasing once the brake is released???
HELP

Here's my experience. Dirt on the piston tends to damage the dust seal (the outer seal). These get torn & jam the piston. You could replace the dust seal or simply remove it. This works ok and the piston isn't adversely affected by dirt or corrosion.

Stuart

[oldktmdude]

   G'day ccsct203, I'm having a similar problem with my '85 1100 at the moment. My problem is only occurring occasionally, so it's fairly difficult to find the problem. You can apply the brakes lots of times when it's parked in the garage on it's centre stand and they seem fine, but take it for a ride and some times they stay on but most of the time, they're fine. 
   So far I've replaced the disc and pads,(which were worn)  thinking that they were allowing the piston to travel too far and not return, also drained and renewed brake fluid and cleaned master cylinder. So far, after a couple of rides it seems fine, fingers crossed I've fixed it.   Pete.

[ccsct203]

ok
I took the rear master cylinder apart and blew out the small .015 diameter hole
put it all back together and it seems better.
I'm wondering ...as I look at the pistons.. one is out further then the other.
This is due to my 18" wheel upgrade.
Could on piston out to far be the issue?
I'm buying a used fj1200 caliper and I'll rebuild it with Randy's kit.
let me know what you think
it is better but not perfect.
Maybe one new pad and one older pad to reduce the piston out too far?

[Harvy]

I'm wondering ...as I look at the pistons.. one is out further then the other.
This is due to my 18" wheel upgrade.
Could on piston out to far be the issue?

Maybe one new pad and one older pad to reduce the piston out too far?

Ahha........ that tell me one of 2 things.......either you have 2 unmated pads in there.....or more likely, the calliper is not sitting centrally over the rotor.

Looking from the back of the bike at the calliper sitting over the rotor...... there is a line in the middle of the calliper housing......it should be sitting perfectly over the centre line of the rotor.

If not, I would suggest a bit of shimming on one side of the calliper mounting arm, and/or removal of material on the other  side to bring it into alignment.

Then shout yourself a new set of pads.

I had a similar issue when I did the 18" Genesis rear wheel..... followed the instructions to the mm on all machining, but the caliper was a mm or 2  too far inboard........a washer between the spacer and the caliper mounting arm solved my problem.

Hope we have finally nailed it.

Harvy

[rktmanfj]

\

...or more likely, the calliper is not sitting centrally over the rotor.

Which is exactly where we were with this same caliper in the other thread on May 26.

Randy T
Indy

[ccsct203]

The rotor is sitting far centered.
there is more then a few mm misalignment.
the inboard piston is extended further then the outboard.
I can't add washers between the caliper and the support bracket, this would worsen the problem.
so what you are telling me is that both pistons should be extended the same distance?
I have two options... machine the caliper mounting tabs where the bolts attach or shim behind the inboard brake pad to "fool" the piston and force the piston back in the caliper the same distance  as the outboard piston.
Would both of these options work?

THanks guys

[RichBaker]

The way a brake caliper works, it shouldn't matter if it is offset slightly to one side..... once you pump the lever a few times, the pads will be pushed out to the rotor, and if the seals are good, they'll retract the piston a few thousandths. There's got to be something preventing this... either crud on the piston, or something preventing fluid from returning to the MC/reservoir.

[Harvy]

I can't add washers between the caliper and the support bracket, this would worsen the problem.
so what you are telling me is that both pistons should be extended the same distance?
I have two options... machine the caliper mounting tabs where the bolts attach or shim behind the inboard brake pad to "fool" the piston and force the piston back in the caliper the same distance  as the outboard piston.
Would both of these options work?

THanks guys

Not between the calliper and the support bracket.......down at the axle is where you add the washer if necessary - between the bracket and the spacer will move the bracket/calliper assembly out......... and machining of the bracket where the axle passes thru it on the inside, will move the entire assembly inwards.
I would not be shimming anything in the calliper myself, just get it sitting centrally over the rotor and all will be good.

Harvy

[Harvy]

The way a brake caliper works, it shouldn't matter if it is offset slightly to one side..... once you pump the lever a few times, the pads will be pushed out to the rotor, and if the seals are good, they'll retract the piston a few thousandths. There's got to be something preventing this... either crud on the piston, or something preventing fluid from returning to the MC/reservoir.

Slightly being the operative word........ it only needs to be slightly more than slightly and the rotor will be rubbing on one side or other of the calliper.

Harvy

[ccsct203]

the offset is more then slight
I would need to shim out the caliper bracket
I don't know if there is enough room to add any shims in there
I'll check the difference with calipers tonight and then I have a dimension of what I'm dealing with
I'll try to take a pic also

[MOTOMYSZOR]

Very old post but similar problem:

Yesterday I cleaned whole rear brake system (I have Fazer 1000 calliper and FJ1200 ABS MC):
- calliper (I took out pistons and I cleaned all inside)
- master cylinder was disassembled and cleaned. All parts inside in really good condition.

Today after 5 minutes ride I started feel strong drag on rear brake. After slow return home rear disc was really hot. When I unbolted calliper It was impossible to push back pistons - but it was easy when I unscrewed bleeding screw. Also when I push brake pedal it will pump out brake fluid as it should.

So guilty can be brake line or MC. But I am not sure which one is guilty that it works as one way system....

[Pat Conlon]

There is a relief port in the m/c that's clogged. This port releases line pressure when the piston retracts.

[MOTOMYSZOR]

those relief port is microscopic. How You think: drill it to 1mm size will be good idea???

[Pat Conlon]

No...I would not drill anything Karol.

Just another disassembly and cleaning. This port resides in the piston bore and connects between the pressure side and intake side of the circuit.
Pay attention to the remote reservoir and the connecting hose. Any crud in there can (and will) settle down into your m/c.

This is also common on the handle bar mounted m/c's (clutch and front brake) The relief port is located under a plate at the bottom of the reservoir. For through cleaning you have to remove these plates and get the accumulated crud off the bottom. With the plates out you can see these relief ports working. When you squeeze and release the levers, a little fountain of brake fluid will squirt up out of these relief ports as the line pressure is relaxed.
The plates are there to prevent this fountain of fluid from causing you headache and damage.

When I converted over to non hygroscopic DOT 5 I removed these plates. I no longer worry about brake fluid spills.

Hope this helps.