Master cylinder - 81 kz750 Ltd

Well, I'm back with a new set of questions. I opened the master cylinder on my 81 KZ750 Ltd. project bike. The fluid was very dark, and thick/jelled around the edges of the master cylinder. The fluid in the sight window had also jelled. Can this be cleaned out with new fluid? Is there another technique? Where can I find rebuild kits? How about brake lines - where can I get them and what kind would you recommend? I know this is alot of questions. Hope some of you have some answers. Thanks for your time. Greg

do your brakes work at all?if they are still operational i would try cleaning out as much of the old stuff you can from m/c(remove gastank 1st though and cover everything else thats painted.then top off mastercylinder and bleed brakes untill you see clean fluid coming out of calipers.if your brake lines are dry rotted z1 enterprises probably has what you need or knows where to get them;) goodluck,happy wrenching!

del

First the down and dirty way -- just suck out the jelly, crud, rust, old fluid, etc., from the reservoir, clean out the reservoir as best you can with fresh brake fluid (both the larger hole and the tiny hole at the reservoir bottom should be clear) fill reservior with fresh fluid, remove or loosen the bleeder valve on one caliper, and keep pumping fresh fluid through until only clean fresh fluid comes out of the bleed valve hole. Then tighten or replace the bleed valve and repeat with the other caliper. Then bleed all air from the system and keep on bleeding until you feel a good firm lever that doesn't squeeze against the handlebar grip. Same procedure with the rear brakes.


Notwithstanding the above, the following should result in far more peace of mind (at least it did for me).

Just guessing reference is to the front master cylinder, but regardless, the other is likely in the same condition (and calipers as well). Hope a shop manual is available for disassembly of the masters because the circlips, split metal rings, keepers, etc. can be rusted and hidden buried underneath all the crud especially in the area where the brake lever contacts the piston (some parts likely not reuseable). With enough luck, perhaps a good cleaning will suffice and the piston and rubber cups will remain useable, but as long as you're in there, may want to replace those items as well. For cleaning, I use common rubbing alcohol in a spray bottle (common sprayers screw right onto the plastic alcohol bottle) and compressed air is also very handy. Be careful not to mar the inside cylinder where the piston goes back and forth, and carefully inspect this area for any pitting. If pitted, you may use very fine wet sandpaper on a wooden dowel or other non-metal tool and wet sand the area to get it smoother. Clean inside the reservoir and clear both the larger hole and the tiny hole (compressed air). Clean everything with alcohol -- dry well (compressed air is good) -- and coat the piston, rubber cup and cylinder with fresh brake fluid and reassemble.

Now to the calipers, which are probably also just as nasty inside especially behind the piston. May need to first remove the front wheel. Be careful when using compressed air to remove the piston -- stuff a rag inside for the piston to hit when it comes out hard and fast (keep your fingers in the clear). With luck, the caliper piston will be reuseable, but consider replacing the rubber parts (fairly expensive). Check to see if new pads are needed. Clean all caliper parts with alcohol, blow dry, apply fresh fluid to the large rubber o-ring that fits around the piston, and reassemble the caliper. Consider using a thin high temp grease coating on bolts where the caliper half slides back and forth.

Now to the brake lines. I use alcohol to clean the inside of the brake lines, then blow dry. Best to have all the alcohol completely removed from all parts and inside lines before hooking everything all back together.

At this point you should have a pristine master cylinder assembled and attached to the handlebar and pristine calipers assembled and attached to the forks. When attaching the brake lines, you may use new banjo bolt washers, but I've never had any leak problem just using the old banjo bolt washers (maybe just lucky).

Now you are ready to fill the reservoir with fresh brake fluid (probably DOT3 -- it might be DOT4 -- use what it says on the cap), check for leaks, and embark on the joyful adventure of bleeding air from the brake system.

Z1 Enterprises lists some '81KZ750ltd brake parts and might be able to refer you to another source for anything Z1E doesn't carry.

Exasperation (and screwing up) is highly likely without the shop service manual or at least a complete parts diagram.

Also I would recommend your searching the archives for additional and better information and answers.

Good luck.

del