Rear brake from hell - 1978 KZ1000 LTD

Hey everyone, new to the site but this seems like the place to be with regards to Kawasaki knowledge base....

My problems began when I decided to replace the stock rubber brake lines on my '78 KZ1000 with steel lines (the old ones were beginning to corrode pretty bad). The front brakes went back together no problem - the rear one could not be bled no matter what i tried. I even ended up stripping out the bleeder valve and had to replace the caliper. After doing that I completely tore apart the rear master cylinder to check out the internal parts - everything looked to be in good condition and there didn't appear to be any blockage so blew everything out with compressed air, re-assembled it and bench tested it out, seemed to be pumping fluid so I put it back on the bike. After a long session of tag teaming it with a vacuum bleeder and pumping the brake I got it working...temporarily.

then a week later I had new tires put on, after the rear wheel was taken off the piston would not retract enough to get the wheel back on. I had the tire guy just take the pads out and I rode it home, and then disassembled the rear brake again. I checked out the caliper and it seemed fine, no leaks and piston was moving. So now thinking there was something wrong with the master cylinder I ordered all new internal parts and completely rebuilt the rear master cylinder. Put everything all back together and still unable to get the damn thing bled, tried vacuum bleeding, reverse bleeding, still could not build any compression in the caliper.

Finally I waved the white flag and brought it into a shop that works on older bikes. They were also unsuccessful at getting it working and could not figure out exactly why. The only thing they suggested was that the bore in the master cylinder was possibly slightly too big and the piston was not moving enough fluid to build compression in the caliper (even though it's not leaking any fluid).

Anyway, before I drop another $300 on ordering a whole new master cylinder was wondering if anyone on here had any experience or similar issues/insight with this setup? Or could I possibly replace it with a different braking setup for less $. Any help would be greatly appreciated; I'm about to miss another whole riding season...

Check the hole in bottem of reservoir where fluid returns after you release brake to see if its clogged.

Yup...second that. My friend was having the same issue with his front brake cylinder. Brought it over to my house and we "discovered" the second tiny hole. Looked to be just a small depression. I kept digging at it and it turned into a hole. Put it back together and worked great. Don't some of the newer designs have little reed valves looking things built into the piston to do the job of that little hole?

Yep, yep, small hole in master plugged. Had the same deal on my front mc. It's a little bitty hole. Had to grind a finishing nail to unplugit. Good luck

Just bleed mine a month ago on my 78 LTD when I installed the electric pressure sensor banjo bolt and air was harder than usual to get out. Guess I will look for the little hole too... But the stock design is sound. Been hauling my ass down from triple digits for many moons.

My son read that if you precote the inside of the hoses and everything else before the rebuild air wont stick to it.
He used a syringe to cote everything and we had the front brake with fresh hoses powered up in about 5-10 mins.

Hey everyone, thanks for the thoughts....I've definitely checked the holes on the master cylinder - I've had that thing apart like 5 times now. I'll try to include some pics of the setup - the MC is connected to the piston mechanism so the path for fluid is pretty considerable as compared to the front one...





I'm almost leaning towards trying to find an alternative braking system - they apparently didn't make this set-up for very long (shocking) and that's why the replacement master cylinders are so bloody expensive. And if I spend that kind of money and it STILL doesn't work I'm gonna have a meltdown. :lol:

Does anyone know if this braking system can be replaced with anything newer? (i.e. 80's models?)

If you break the hose loose at the master does the caliper return? If so is your push rod too tight? Maybe the cup is too long and covering the release hole. Just some ideas.

Is your new brake line kinking or collapsed on the inside? If the caliper isnt returning pressure isnt bleeding out of the system

Haven't tried the caliper return test....maybe I'lll give that a shot before I throw in the towel. I know the push rod is set right and the brake line is fine...the mc moves some fluid through the line but apparently not enough to pressurize the caliper. Difficult to tell where the cup is inside the mc but it's all brand new components in there and unless the mc is machined wrong shouldn't be blocking anything...