Yamaha R6 Forum: YZF-R6 Forums banner
1 - 2 of 2 Posts

438 Posts
Discussion Starter · #1 ·
So after doing my mid summer light overhaul, new tires, pads, and some other maint. stuff.

My rear brake isn't pumping up. The piston comes out and presses against the pad, however not pushing fully on the pad to actually exert pressure onto the rear rotor.

Here is what I have done so far..

-Replaced my master cylinder with a good, known working used one. As I found that my old one would blow bubbles back into the fluid reservoir. The new-ish one does not blow any bubbles whatsoever.

-Bled my brakes countless times, NOTHING but a stream of fluid coming out, I have used both a gravity bleeder, and what could be called a vacuum bleeder(the one with the pump to help pull the air out)

-Replaced the seals in the caliper itself, when I pulled the piston out, I noticed some rubber residue, and wear marks on the piston itself.

-Cleaned the rear caliper inside and out, even the grooves where the seals go before I put the new ones back in. I used a non-abrasive rag and lots of brake cleaner. There is no pits or corrosion on the piston itself, or the bore that it goes into.

Now, here are my thoughts...
-I have not replaced the brake line just yet, It looks fine, no visible cracking, and also it does not flex when I push the pedal down

-When I replaced the rear pads, I did not put the four shims on the pads themselves. At first I thought this was my issues, however, my old pads were thinner than the ones I replaced them with. I've also spoken to a few shops and they said the only reason the shims were on there was because of the quality of the metal used on the OEM pads.

-When I put the piston back in after replacing the seals, I did put a little brake fluid on the seals to sort of lube them up. Also, I pushed the piston in flush with the bore of the caliper, did not force it beyond that. For some reason I'm thinking it may have snagged on a seal and that may prevent it from extending.

-I have the adjuster on the master cylinder set far out so this way there is a longer stroke in the master cylinder.

Sigh, with all of this being said, what are your guys' thoughts?

Ideas are appreciated

7,324 Posts
line. you said that's the last thing you haven't touched. I would gravitate to the line being bad. some dirt or something in it. maybe. the old master was bad maybe is shoved some of the pistion rubber seal into the line.

and check to make sure your brake lever isn't binding. (it goes down all the way and back up without any kind of grinding or snagging)

also check the caliper bracket is on the swingarm correctly. this will make it sit crooked if it's not on the tabs on the swingarm.
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.