Rear brake help!

[benwall]

I have a beta rev 3 2007 250 and recentley the rear break has stopped working, i have narrowed down the fault to being some were in the intake/inside the rear master cylinder/pump.

can any one recomend what to do? or has anyone else had this problem?

I imagine im going to have to fork out and buy a new master cylinder so is it possible to replace it with a universal brembo one instead of a beta one? or does the beta one being made for trials react diferently to the brembo one?

http://bikeswoop.com/Brembo-Rear-Master-Brake-Cylinder.html

Thank You

Ben Wall

Edited May 27, 2011 by benwall

[betarick]

Just get a master cyl seal kit! & have fun bleeding it out

[nzralphy]

Right-o Ben

Have a bottle of brake fluid, an empty catch bottle, clear tube to send excess fluid to the catch bottle, & 8mm spanner ready

Adjust the brake leaver so there is a little clearance to the master cylinder piston. Really important.

Remove the fluid reservoir cap/lid.

Carefully force the pistons back into the calliper body and jam some wood between 'em to keep them still.

Remove the pads - pads become useless with a drop of brake fluid on 'em

Hang the caliper so the bleed nipple is pointing up hill.

A - Undo the bleed nipple while applying a little pressure to the brake lever...... (put the tube over the nipple to take the excess fluid away)

B - Close the bleed nipple and release the brake lever and check the reservoir is full

Repeat A B A B A B A B A B A B A B A B quite quickly until air bubbles stop coming out of the bleed tube.

With the Beta be prepared to do this for 10 minutes or more so keep recycling the fluid.

Nip up the bleed nipple put your pads back in a try it out.

if that doesn't work (it does every time for me) you may need a master cylinder rebuild kit from the Beta parts man.

Wash up with a water rinse.

Good luck.

Edited May 27, 2011 by NZRalphy

[02-apr]

It may be worth noting that if Ralphy's method does not work, and there is actually no seal problem, that using a syringe to push the fluid from slave to master cylinder often removes those elusive bubbles. Just be sure you don't squirt fluid out of the master cylinder on to the the paintwork!

[rallymadsam]

Right-o Ben

Have a bottle of brake fluid, an empty catch bottle, clear tube to send excess fluid to the catch bottle, & 8mm spanner ready

Adjust the brake leaver so there is a little clearance to the master cylinder piston. Really important.

Remove the fluid reservoir cap/lid.

Carefully force the pistons back into the calliper body and jam some wood between 'em to keep them still.

Remove the pads - pads become useless with a drop of brake fluid on 'em

Hang the caliper so the bleed nipple is pointing up hill.

A - Undo the bleed nipple while applying a little pressure to the brake lever...... (put the tube over the nipple to take the excess fluid away)

B - Close the bleed nipple and release the brake lever and check the reservoir is full

Repeat A B A B A B A B A B A B A B A B quite quickly until air bubbles stop coming out of the bleed tube.

With the Beta be prepared to do this for 10 minutes or more so keep recycling the fluid.

Nip up the bleed nipple put your pads back in a try it out.

if that doesn't work (it does every time for me) you may need a master cylinder rebuild kit from the Beta parts man.

Wash up with a water rinse.

Good luck.

Sorry to drag this old thread up, but I thought it was better than starting a fresh, one question I have is, what do you mean by "Adjust the brake leaver so there is a little clearance to the master cylinder piston. Really important."?

Cheers,

Sam

[pindie]

The biggest advice is patience patience patience when bleeding stuborn brakes. To get air out of a small pipe you have to think like air in a small pipe!

[rallymadsam]

My rear brake was fine last time I rode, then got the bike out the other day, rear brake stuck on, couldn't free it, so bled some fluid out, but now got no brake at all, and I've had fluid coming out of the caliper bleed nipple with no bubbles at all in it, for quite some time, brilliant. Think I'll try the above.

[stork955]

To answer Sam, all m/cyls have two ports between the reservoir and the actual cylinder.The big one feeds fluid into the area between the cups(seals) and the caliper, and the little one allows expanded fluid to enter the m/cyl as the brakes get hotter. As you press on the brake (or pull the lever) the big hole closes first,followed by the small hole (transfer port). Often in an attempt to correct poor brakes, people adjust the freetravel of the pushrod to push the piston into the m/cyl and closing the large port. The m/cyl cannot fill properly. In extreme cases both holes are closed which is really bad. Bleeding becomes impossible. These ports must be open at rest for the system to work properly. Have a look at http://www.agcoauto.com/content/news/p2_articleid/129 (scroll right down) for a picture. It is a tandem car type, but the principles are the same -imagine that one half is cut off.

Cheers,

Stork

[pindie]

Good point. I always back of all adjusters etc to minimum before bleeding so I know I have full movement/MC travel for the bleed.

If you bleed every six months it is a five minute job to do front and rear brakes.