Rear brake siezed

[Dave G]

My back brake has jammed (again) and after taking off the caliper and looking at the pistons they didnt seem too crappy.It was really hard to force them back in a bit though,and after thinking about this a bit I suspect it may be something to do with the master cylinder.Before touching it the lever had no resistance and flopped up and down -no pressure to return it,this also meant my brake light was permanently on.
After forcing the pistons back into the caliper I noticed the pressure had returned to the lever ,though from past experience I know this'll only work once or twice before giving up again.
I'm no mechanic and have effectively reached the limit of my skills here,so what do I do next? The brake is no longer dragging but as I use mine I dont like riding without it,Ducati Glasgow is an hour away and a real pain in the @rse to get to from here but if thats my only option so be it.
Will I be looking at a replacement master cylinder? and what'll that cost me?.....or have I missed something simple?:o

[Murray Mint]

Dave

I’d be very surprised if it were the master cylinder causing this problem, it sound more like calliper problem as you mentioned that it was very difficult to push the piston back in, the master cylinder dose not pull the piston back into the calliper. Have you checked the pistons themselves? Is there any sign of rust around them as this could prevent them from returning into the calliper, the pads should run with very little gap between then and the disk. I would suggest that the rear calliper is striped, cleaned and checked for free movement.

Hope this helps.

Murray Mint

[Marty916]

There have been numerous cases of seized rear brakes here in the US. Some have been caused by faulty master cylinders and some by the caliper. I recommend starting with a good cleaning of the caliper as suggested by Murray. Then do a thorough bleeding of the system (with the caliper off the mount to allow the bleeder valve to face the correct direction). If you still experience brake problems it has to be the master cylinder. There are only two components in the system so process of elimination is in order. Best of luck!

[Nigel Booker]

Dave,
I would get it looked at asap my 748 had a similar brake problem and eventually I had the rear caliper and brake line melt. Turned out that the master cyclinder was not returning correctly and constantly kept the fluid to the caliper under pressure.

[Felix]

Yep, I agree with Nigel. The symptoms you describe lead me to believe that the fault is in the master cylinder. It's not returning properly, hence you can't push the piston back in the caliper and the brake pedal feels "loose".

[Rip]

It might be obvious but have you adjusted the rear brake pedal recently? Not enough free play even though the wheel turns freely when cold will heat up and expand the disc when ridden to cause binding. This lesson cost me a new caliper and rear disc, aahhh.

[Nigel Booker]

Dave,
if you have adjusted the rear brake lever it would pay you to slacken it back off asap. If you attempt to get a better rear brake by adjusting the amount of travel in the pin and clevis on the master cylinder you can over adjust the pin and not allow enough return movement on the cylinder. This has the effect of cutting off the return flow for the brake fluid and keeps the fluid into the rear caliper under constant pressure. This in return results in heat build up in the caliper, disc, brake line and master cylinder.

[Jinx]

Hi Dave,
My Bro had this problem. He'd readjust the whole system (even replaced the caliper at one point!) and it would lockup again on the next journey.

The solution was to use 'Screw-lock' on the little adjuster screw(4mm?) that's at the brake pedel (I think it switches on the brake light). It was vibrating out by a millimeter or less everytime he applied the brake, and would eventually just lockup the rear wheel.
Good luck.

Jinx.

[Edited on 13-8-2003 by Jinx]

[Dave G]

....thanks for the suggestions so far.
I've removed the master cylinder now and my mate has suggested a new seal kit,but the haynes manual states that brembo regard this as a non servicable item though it does add you can get aftermarket overhaul kits.
What are my options here?
How much would a new cylinder cost?

Is this a straightforward job?

Where will I start looking for a seal kit?
(cant imagine ducati glasgow will help much here if brembo say replace the lot)


I may replace the pipes while I'm at it.
:o:P:o

[Nigel Booker]

Dave,
I tried to get seal kits for the master cylinder and caliper but had no luck. If either is faulty I would ring around a few breakers and see whats available. I got an almost new rear caliper for £20 and a master cylinder for £15.

Try http://www.part-locator.co.uk/