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2007 Rear Brake Pedal

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Help needed!

I disconnected my rear brake master cylinder (the part connected to the frame - not the reservior) to fit a pair of new carbon frame gaurds. To be honest I'm a bit disappointed with the gaurds - the master cylinder holes had to be filed out to make it fit as they were out of line etc and the air box cover certainly does'nt fit as it moves the rubber air box to carb hose out of line.

On reassembling the bike with the frame guards in place the master cylinder appears slightly out of line compared to the brake pedal piston. I've had a good look and this appears to be a manufacturing tolerance in the cylinder and has probably always been there.

After bleeding the rear brake I have lost the free play in the first 5 mm of the pedals movement. The pedal is slack and has simply dropped down the 5mm, although it can be lifted up by hand. Also the pedal is slow to return after the brake is depressed. Having said all that the effectiveness of the brake is still pretty good.

Immediately after the installation I depressed the brake pedal and it completely failed to return to position. The piston in the master cylinder appearred to be stuck and the only way I could free it was to force the rear brake pads apart.

Any ideas how I return the brake pedal to its normal position and return its movement to what it was before? I've tried bleeding the brake until I'm pulling my hair out and I dont think its air in the system.


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Hi there,

It sounds like you are stressing the master cylinder and maybe warping the unit after fitting the guards and this is causing the piston to stick. Have another look to see if you can mount the cylinder in an unstressed situation with the guards in place, if not then you will have to remove the guard. I have used 50mm wide thick black electrical insulation tape for many years on my PRO frame tubes which looks good for a long time and prevents any scratching to the frame. Easy to replace too! If you take your time, you can easily follow the frame tube contours when fitting the tape so that there are no creases.

Bye, PeterB.

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Not quite sure I totally understand how things got shifted around here or why you had to bleed the rear brake, but I can tell you that if you did manage to get air in it you must break loose the top banjo bolt to the hose to get it out, otherwise you will have a real fight getting it out and work forever trying!

Hope that helps! :rolleyes:

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I will take a run at it as it is not all adding up anyway...

OK, how about, somewhere in this endeavor, he pulled the line off the master, and has it kicked around on the master to where it contacts the frame? Beats me, would have to look if it is even possible, but I bet this is going to be a case of look for the last thing that got "fixed"

If it were at my house, I would pull the master, and isolate the problem one step at a time.

Actuate the master on the bench, clean? Full return, no grit or grunge pushed up under the boot from handling it? I would go ahead and disassemble and clean if it was mine.

Brake pedal, bearing clean? Smooth operation, not hanging on the new gaurd you stuck on there somehow?

I will bet you will see the problem by this point, if not remount the master, insuring that it sits flush against the frame. I have not done an 07 but on my bikes I take the mc banjo bolt and swap it with the rear caliper bolt, lets me tighten the banjo while the master is tight against the frame.

Back bleed, break each joint, see if the problem is gone.

Good luck.

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