Master cylinder

[Dman1952]

The piston in my 72 XS is not working the notch in the rubber I’m assuming that is the problem. Probably not going to find a replacement.

 

[Grewth]

I don't think you'll have much trouble in finding a replacement seal kit, although maybe not a genuine Yamaha job.
Important thing is the state of the bore in the m-cyl body.
Is it scored or corrosion pitted ?

 

[cra-z1]

https://www.mikesxs.net/master-cyli...MI4pThg8Pq-AIVlBh9Ch3yjwQHEAQYASABEgLY5fD_BwE

 

[toglhot]

Early models had two different sized masters, one being metric at 16mm, the other being imperial at 5/8" (15.785mm), so they are not interchangeable. I'd suggest you get out your micrometer and measure before ordering a kit. There should be a number forged under the reservoir. I chucked mine away, so can't remember the exact setup, but it was imperial and had two seals, one end had a plastic thingy on one end similar to the one you've pictured. The one cr-z1 linked to is imperial but doesn't have two seals or the plastic thingy on the end so may not work.

 

[arcticXS]

There used to be someone in the UK, who machined out corroded master cylinders, and installed a bronze or stainless liner in it. That also would give the great option of reducing the bore to a more suitable size, like 13 mm.
That is the size of Brembo MC that I use on my 74. RD 350, which has the same dual 48 mm piston caliper as the 72-76 XS/TX.
(Which btw. is a much better caliper than the single piston caliper on the 77 and later models)

 

[willis]

Most replacement pistons are different than the originals. When I rebuilt my 75 this really threw me for a loop. It may look different but still functions the same. Have a read on my findings here. http://www.xs650.com/threads/75-front-brake-refurbish.54088/#post-580979