1979 KZ650 SR rear master cylinder woes

Doonie, was wondering which master cylinder you bought off ebay?

Original Post:  "So here's what i ended up doing as I was getting nowhere with the original master cylinder. I bought this cheap knock-off on Ebay. It bolted on directly (different bolts, no big deal) which simplified things. I had to modify the bottom end of the new MC but didn't do anything to the bike that would prevent me from putting the original back on. I simply extended the bottom of the plunger rod and then rotated the barrel bolt so I could thread up from the bottom. The reservoir bolted on very easily right next to the fuse box. Bled the brakes and all is good. Just wanted to provide an update and thank everyone for all the great advice and taking the time to assist. Really appreciate the help !  Gary"

Well, I got lucky on my bike. I took the whole bike out to a vintage Kawasaki expert in Valley, NE. He took the rear master cylinder back apart. He found that the piston was actually usable. He used the cup and seal out of a front master cylinder rebuild kit. He said all H2's and Z1's are 1/2" pistons for the single disc fronts and 5/8" pistons for the dual disc fronts. To be able to stretch the new seal onto the old piston, he lubed up the seal and used a heat gun to soften it. So far my rear brake is now working fine.