A forum for owners of Yamaha TTR250 trail and enduro bikes!

Sorry about the bad pun but I have spent a few hours this afternoon trying to sort out a TTR250 front brake master cylinder and it's sort of making me feel a bit hysterical 

My mate Jim has a collection of shiny chromed up vintage(ish) Jap bikes and spends quite a bit of time fettling them and trying various improvements.

He read on a forum that the TTR250 front brake master cylinder was a good mod for his Yamaha XS650. Apparently the smaller bore of the TTR one works better than the original.

I had a couple of spare ones here that were waiting to be repaired and refurbished so dug them out for him to look at. Both of them were suffering from the common problem with rusted and seized cap bolts. The heads had been drilled off to allow the cap to be removed. That left the top of the offending threaded part exposed but not long enough to get a grip on it with pliers. The next best solution is to use a MIG welder to weld a washer on to the remains of the screw and turn it out using the washer. A photo of the welded on washer is pictured below to illustrate what I mean.

It worked on three out of the four which can't be bad. Fortunately for Jim, both came out on the best master cylinder so that was the one we would use. This is how they look when unscrewed from the master cylinder reservoir.

That problem solved, we then stripped out the piston to replace the seals etc using one of Steve's kits - see here

We installed the kit and then the lever to test it was working OK and that we had pressure. There was something odd in that the adjustable bolt on the different levers we tried just didn't seem long enough to reach the head of the piston assembly 

It was only after wasting about half an hour trying to figure out what the problem was that we noticed something 

Do you spot anything wrong with our piston pictured below?

Yep, it was about an inch shorter than it should be and, goodness knows how, the top of the piston that engages with the lever had been broken off 

This is what it should have looked like....

The break was so clean that we just didn't notice 

Anyways up, we swapped out the piston and completed the rebuild and, hopefully, the job's a good 'un 

Brian