I started my 3rd trial today but didn't finish due to rear is no movement whatsoever in the caliper but the reservoir is full. No sign of fluid leakage anywhere. However the shaft from the brake pedal into the master cylinder is rattling around at the master cylinder end. The bike was held upright with a piece of wood resting against this shaft - I wonder if its damaged the master cylinder? Any ideas

Is there a rebuild kit for the master cylinder? Could it just need bleeding? If so can anyone provide a dummies guide as I've read it can be difficult on a trials bike.

Thanks in advance

Must be something in the air.

I'm going thru my own brake problem but mine is in the front.

The only way to make sure you are trouble free is a rebuild. You may get by for a while but without normal maintenance we are all heading for fail.

We really need a better description. Is the brake stuck on or not actuating? There are rebuild kits for the rear master cylinder but you probably don't need one if there is no leakage. A misadjusted brake is the most likely problem but can't guess without a clearer description of the problem.

Sounds like the master cylinder piston may be stuck / not returning in which case a strip and clean should sort it.

You can try operating the master cylinder with a screwdriver, you should feel the piston rise and then return.

If it's stuck at the top as Dadof2 states, it's stuck and needs a strip and clean at the least.

 

Yes, there are rebuild kits available, they aren't expensive and are available from either a Beta importer or many of the online spares shops.

Watch out for the which year yours is, I seem to recall Beta altered some of the hydraulics at some point, 2005 rings a bell.

 

When you've cleaned/rebuilt it, set the adjustable actuating rod from the pedal with a few milimeters of free play before it starts to operate the cylinder.

Over adjusting this rod will cause the brake to jam on when it's been pumped a few times, the play is needed for the cylinder to return fully otherwise it'll pump up and lock on.

Same goes for the clutch and front brake levers.

 

Due to the small size of the master cylinder, it can be a pain bleeding out, it moves very little fluid so an air bubble on the flat section of hose will never pump out!

You can remove the caliper, hose and master cylinder as one and hang it up right so fluid runs down.

Or

With a large syringe from the chemist and a small rubber pipe, gently back bleed the system from the caliper bleed nipple.

Just loosen the nipple, attach the syringe and pump the fluid in until it stops spitting in the ressie, then nip the nipple up.

 

Also worth noting the 4 piston calipers tend to jam once the pads have worn down a bit.

The tiny pistons don't like extending too far out of the caliper before they twist and jam as they can no long stay straight in the bores.

They tend to do this before the pads are completely worn out.

Edited June 12, 201511 yr by goudrons

Thanks for the responses and in particular the bleeding guide on last post. To answer earlier question - the caliper is not actuated - wheel is spinning freely.

As suggested in most posts - removal of the master cylinder, clean, rebuild and bleed seems to be the way forward. My first time on a bike (done a few cars) so wish me luck!

Thanks again

I've just ordered a rear master cylinder seal kit because the MC piston doesn't return properly so will be doing a rebuild too.

 

I've rebuilt the caliper already and I can tell you that the rear is a PITA to bleed (as stated because of the stupid loop in the brake line and the small piston). It's a PITA to remove too but just bite the bullet and take it off completely and hang it vertically. 

Edited June 12, 201511 yr by al_orange