Seized rear brake on 03, 749.
 

At the end of May the rear brake seized at speed and blew the nipple. Brake was not being used at the time and there is plenty of play on the pedal. Under guarantee, so the dealer changed the disc & calliper & fitted new seals in the master cylinder. Has been fine since, till last Sunday when at 30 to 40 mph seized again. Left for 10 minutes and it freed up completely.

The master cylinder is very close to the front exhaust pipe but the bike runs at normal temperature and the rear brake hardly gets used. It’s going back to the dealer today (now out of guarantee) but has anybody any ideas why or had this happen to them?

Never heard of that one Duncan - well done, you've discovered a new one.

Have a beer on me :)

I can think of two possibilities:-

1. Could the operating rod be adjusted in too far?

If the travel of the pedal is reduced by too much by extending the adjustable rod, then the master cylinder piston will not return far enough to clear the relief port. The system will trap pressure if it heats up and the fluid expands with nowhere to go.

Try putting a little bit more slack in the travel of the pedal.

2. The other possibilty is corrosion in the master cylinder bore due to water in the fluid settling at the bottom of the system. I had to change the rear master cylinder on my 851 last month because the piston was seized in the bore and would not return. There was too much pitting to clean it up and change the seals.

Good luck!

Mike

I had a similar thing on a (well) used ST2. Rear brake seized on and I was forced to a stop. Couldn't even get out of the trafiic until it cooled down and released enough to roll it. Who say those rear brakes don't work!!!!

I never could get it sorted, until I got hold of a spare caliper-master cylinder off another bike and put that on complete. Not a very technical way of problem solving, but I was getting desperate at that point.

Problem is - once it has seized on it will ahve generated so much heat that it'll boil the fluid. You're fighting a losing battle then because it'll not work properly anyway.

Good Luck

If the work was carried out in May (this year?) then does it not still come under warranty?
Whats the warranty deal on dealer installed parts?

There is the usual 12 month warranty on anything fitted by the dealer, regardless of the warranty on the bike itself.

Same thing happened on my 996... brake locks on and releases again once it cools.

Turned out to be adjusted wrong at the pedal, like in mikesps's scenario 1.

Nelly set it up properly and it's not bothered me since.

Shouldn't matter whether the bike is still under warranty or not.

Your problem first originated whilst the bike was covered , so the dealer is under obligation to sort out an existing problem!

I agree with mikesps in that it is probably a problem with the adjustment on the operating rod!
I had a similar problem on a CBR i used to own where rear brake wouldn't release fully when warm!
Solution........Adjusted the pedal up slightly to increase play!

Not the same bike, i know, but arn't all systems similar?

Thanks for the replies, Dealer is going to fit new calliper again as it blue the seals & new master cylinder. Though I did find out that nothing was done to the master last time. There is plenty of play on the pedal & it has been at that adjustment since just after we bought it in 03.

So just have to hope the new master does the job as a seize while banked round a bend could be hairy to say the least, especially at track day angles of lean.

Cheers guys