Evo Back Brake

[westygas270]

Hi all has anyone else had this problem: got a 2010 290 beta evo, after couple of trials back brake was binding causing it to lock on and ended up melting seals e.t.c. had all of the pistons e.t.c replaced and has been ok had play in brake to. Just been in garden on it and seems as its trailing again, if you spin wheel can hear it binding play in back brake doesnt seem to be there anymore, dont want to ride it again and end up having to replace pistons e.t.c again any help please;

[fivemeister]

My 09 evo 4T has just gone the same way. First heard it squeking every wheel revolution then on a long lap it must have built up so much heat that the fluid expanded and siezed the brake on.

I have previously noted that the evo brake discs are fixed as opposed to the floating discs on the previous rev3. It was always going to be a backward step on a trials bike (with the degree of abuse and potential for the wheel / disc to be out of true) and I can't work out the logic of it?

[westygas270]

Yea mine was exactl the same then rewed the pistons and seals, pads, and new disk and was ok plenty of play in the brake and just seems to of gone the same again, its like the pads are allways are to close to disk

[stork955]

Gday guys, stating the obvious I know but there must be clearance between the pushrod and the piston near the pedal. After this, if something is blocking the transfer port in the master cylinder you will get the same symptoms. This hole is tiny and takes nothing to block. Of course the caliper must not be seized either! It might pay to double and triple check this stuff before fitting parts that may not actually fix the problem.

Cheers,

Stork

[jse]

Gday guys, stating the obvious I know but there must be clearance between the pushrod and the piston near the pedal. After this, if something is blocking the transfer port in the master cylinder you will get the same symptoms. This hole is tiny and takes nothing to block. Of course the caliper must not be seized either! It might pay to double and triple check this stuff before fitting parts that may not actually fix the problem. Cheers,

Stork

I'm with Stork. Something or some condition is closing off the system. Usually lack of clearance at the pedal pivot but also a serious obstruction in the bleed hole in the M/C (it takes a LOT of obstruction to block the hole completely) or the rider riding the rear brake (rare, but I've seen riders do it).

If the expanded fluid can't back up into the reservoir, the system is "closed" fluid expands with heat and pressure builds up on the pads, which leads to more heat in the system, which leads to more expansion of the fluid and pressure on the pads and things rapidly come to a stop.

I'd look for the cause before replacing parts.

Jon

[copemech]

Whot they said, It's not returning fluid! Pushrod too tight or MC piston not returning fully to open the return port the likely culprits, next to blockage of the port!

[doctorbeta]

Make sure you've definitely got some positive play in the pedal before it acts on the master cylinder piston. I had the identical problem on the front brake of my 09 250 Evo. A little extra free play cured it. I think its because without play the caliper pistons just and I mean just touch the pads on the disc which warms and expands the fluid. I found out to my cost when coming to an abrupt stop 2/3rds up a steep climb.