KZ650 C2 Rear Brake Woes

I'm puitting a 78 KZ650 Custom (C2) and the rear brake keeps locking up. I suspect the rear caliper is in need of a cleaning and re-assembly with new seals and other soft parts.

I've shopped a number of online vendors of rebuild kits and they all seem to skip over the Custom models (C1, C2, and C3) in there application charts. The only vendor that claims to have a kit that will fit the "C" models is Z1 Enterprises.. They have a footnote in the seal kit page that says Customs use a 38mm piston (and its seal) while all the other 650s with rear discs used a 42mm piston. Z1E says I have to buy a separate 38mm piston seal if I want their kit to fit my bike.

Does anyone know if this is reallly the case? Cs and Ds all had a rear disc. Why would theyKawasaki use different calipers for one sub-model?

TIA 

Hmmm, I'll look into this because i have a few 650 c2 bikes that I'd like to rebuild. The problem I'm having is that that the cap for the master cylinder is plastic and the the screw holes crack out and leak. No replacement parts that I can find. 

No eBay APP ID and/or Cert ID defined in Kunena configurationThose front master cylinders and/or parts for the same are unobtanium (assuming you are talking about the front M/C with the trapezoidal  reservoir). The opaque plastic gets brittle and cracks. I looked for several weeks and only found one that was reportedly functioning. The seller wanted a king's ransom. The diaphragm rots...and if you do find one for sale -- they are very pricey. 

I gave up looking and bought one of these:

It is a knock off of an early KZ1000's and looks period correct and performs well. 

But right now, I am trying to figure out how to keep this rear brake from locking up.

mrgem wrote: I'm puitting a 78 KZ650 Custom (C2) and the rear brake keeps locking up. I suspect the rear caliper is in need of a cleaning and re-assembly with new seals and other soft parts..............

I would thoroughly flush the brake system, and if that doesn't resolve the problem very carefully clean and inspect the rear master cylinder.  It may simply be some crud blocking a small orifice rather than a damaged part.  As long as no water or other contaminants have caused pitting or deterioration of parts I would expect it to clean up ok.  My 1977 KZ650-C1 rear brake master cylinder and caliper have never given me any problems in more than 61,000 miles, but I do flush and refill the brake systems on the schedule recommended in the manual.   Ed

Yes, I agree. It's at the point where you can buy a later model whatever and scavenge the bits you need rather than to be to spec.