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Stiff Rear Brake

  • Thread starter Thread starter Topman
  • Start date Start date
T

Topman

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Started out with sticking pistons and a leak in my Rear M/C boot, determined there was a hole in the boot, as well as bad seals (hence the leaking fluid). Got a M/C rebuild kit, and took apart the rear caliper. Pistons and seals in caliper were in good shape, but there was lots of gunk build up behind the piston from an assumable lack of break fluid changes and sitting for some time.
Thoroughly cleaned and rebuilt the caliper and the M/C, couldn't find a 100% understandable description of "priming" the M/C so I just kept pushing out air and tightening the bleeder until I finally got liquid. Then I bled until I got no air bubbles from either bleeder. Now it's good, aside from the fact that my pedal is very stiff. I can press it maybe an inch, and it works, certainly applies the brakes and stops the wheel in motion, but I can only fully press the pedal when I'm bleeding. Looking at the pads it looks as though the pistons still aren't going entirely back into the caliper after releasing the brake, and that could explain why the pedal can only be pressed so much.

Searching the forums didn't return much, but what I'm looking for is what could be stopping the piston from going back into the caliper? I cleaned it all, the piston wasn't rusty or anything, and there's clearly good fluid flow into and out of the caliper. Any thoughts are greatly appreciated.
 
I would first check the peddle Where the arm goes thru the frame. It could be sticking
 
Keep in mind that the pistons in the caliper don't retract very much when you release the pedal.

When you press on the pedal, they are forced against the disk with more pressure. When you release the pedal, the only thing that pulls them back is the elasticity in the caliper seals, which distort a bit when the piston is pushed out.

This means that the pistons only retract a few thousandths of an inch, but that's enough for them to work properly.

.
 
A properly bleed system does not have much movement in the pedal. As long as the brake is applying, and releasing completely without drag it is functioning properly .
 
Thank you all for the replies, they've been both helpful and informative. I guess I won't know until she's running again whether there's any sort of drag.
 
Not entirely true. put it in neutral with the bike up on the center stand. apply brake, release and see how easily the rear wheel turns.
 
Ok. I've been slammed for being a "newb" before, but I don't have the bike running just yet, still re-assembling the carbs right now. I imagine the free play of spinning the wheel in neutral won't be much different than the free play with the bike off. Currently, with the bike off, I can spin the wheel freely, and apply the brake with 100% success of the brakes, completely stops the wheel, after which I can then freely spin the wheel. Although, with the engine not running and all, as the wheel spins I can hear clear impact of the brake pad with the rotor, not that it's making any substantial difference in the free rotation of the wheel. That being said, I don't know that that won't evolve into drag as the bike begins actually running.
 
There nothing wrong with asking questions and you wont get slammed for being a 'newb,' we were all that once!

You've rebuilt the rear calliper, Master Cylinder, new fluid, check the brake peddle where it goes through the frame is always a good idea as the have a habbit of rusting in place.

Then you have drag on the pads to the disc when its not been used for a while so don't worry about it till you have the bike running again. If there's any sign of rust on the disc it wont run right and bind anyway.
 
Yeah, I was going to say, remember that disc brakes aren't like drum brakes. There's no springs to pull the pads (shoes in the case of drum brakes) away from the disc (drum) so there's gonna be some contact. Just the nature of the beast.
 
Topman said:
Ok. I've been slammed for being a "newb" before, but I don't have the bike running just yet, still re-assembling the carbs right now. I imagine the free play of spinning the wheel in neutral won't be much different than the free play with the bike off. Currently, with the bike off, I can spin the wheel freely, and apply the brake with 100% success of the brakes, completely stops the wheel, after which I can then freely spin the wheel. Although, with the engine not running and all, as the wheel spins I can hear clear impact of the brake pad with the rotor, not that it's making any substantial difference in the free rotation of the wheel. That being said, I don't know that that won't evolve into drag as the bike begins actually running.
Click to expand...

That description sounds like perfectly functioning rear brakes to me!

Yep, it's normal to hear a little ting-ta-ting noise as the pads "kiss" the rotors. They're in very light contact with the rotors at all times.
 
dueller said:
Yeah, I was going to say, remember that disc brakes aren't like drum brakes. There's no springs to pull the pads (shoes in the case of drum brakes) away from the disc (drum) so there's gonna be some contact. Just the nature of the beast.
Click to expand...

I see. It would make sense that I'd over react about the noise, I'm used to drum brakes. Guess we'll see when I get her running. Thanks again!
 
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