TOPIC:

Hi all,
I am currently restoring my father's old 1980 Z1R, and am having a bit of trouble with the front master cylinder/brake system. I have completely rebuilt the front calipers with all new seals and have blown out the brake lines. I used another post on this forum as a guide to disassemble the front master cylinder. I completely disassembled it, cleaned it thoroughly, including the pinholes in the little reservoir on the top of the master, and reassembled it with the same parts as none had glaring visual issues. I put it all back together and put some brake fluid in the main reservoir and attempted to bleed brakes... nothing. I took the end of the brake lines off of the calipers... completely dry. I pulled the brake lever in an attempt to push brake fluid through the lines, nothing happened. I took the brake lines off the master, also dry. The top reservoir of the master had fluid however, it just appears that the piston isnt pushing the fluid into the lines. I am considering buying a replacement piston and dust seal from Z1 enterprises as my next step. Please provide any insight into my situation that you can, anything at all. Please forgive me if I've missed something obvious i'm 18 years old and this is my first bike restoration

There are lots and lots of threads about this. It seems like you already went through them. But I'll say it again. It's critical that both of the two small holes between the reservoir and the cylinder are open and clear. It'll never work if those are plugged.

kzrider.com/forum/5-chassis/569907-z1r-f...tute?start=20#647373
www.kzrider.com/forum/5-chassis/608766-f...servoir-holes#786303

But even if everything is mechanically perfect, if you have air trapped in the system the master cylinder won't draw in fluid. There are tons of recommendations for this.

One thing you might try is to get a vacuum bleeder, attached to the calipers, and pull fluid though the system. Something like this.

www.amazon.com/HFS-Brake-Bleeder-Vacuum-Tuner/dp/B00NP60URE
www.amazon.com/MV8000-Automotive-Tune-up...eeding/dp/B00265M9SS

That's often good for about 90% of the trapped air. But often you're still left with a bubble. At that point the general recommendation is to let it sit for a day or two.
The idea is that this will let air trapped in the fluid separate, and then hopefully float up to the top to the master cylinder.

And many people say to tie the brake lever to the grip so the master cylinder piston is all the way pushed in. Many people here swear by this. It's possible that a common issue is air trapped in that small space between the two master cylinder piston seals. Pulling the lever in and letting it sit for some time would help to let this area fill with fluid.

Another approach to a stubborn system is to use a Mityvac to push fluid into the system from the caliper. You will need some sort of syringe to remove excess from the master reservoir. This will push the air bubbles upward instead of trying to force them downward.

If the brake lines are completely dry, then the little holes in the reservoir are probably clogged (already mentioned above). If you don't have a mityvac or similar, you should install speed bleeders at the calipers, which make bleeding the brakes much easier. What I do is unbolt the caliper & shim the brake pads as tight as possible, then elevate the caliper with the bleeder pointing upwards, so the fluid can push the air out easier & minimize bubbles. This is especially useful if you don't have speed bleeders.
edit: connect clear tubing, of course, routed to a clear container w a few ounces of clean brake fluid.

Warning: protect the fuel tank & other stuff from brake fluid as Dot 3 will ruin paint. When shimming the caliper or pushing on the piston with the reservoir cap off or loose, brake fluid will squirt out the little reservoir holes & may leak at the cap. If the system is dry, then no problemo.

TexasKZ wrote: Another approach to a stubborn system is to use a Mityvac to push fluid into the system from the caliper.

Actually, since the Z1R has a remote reservoir, you could connect the pump in place of the reservoir and pump fluid into the master and out the calipers. This might be a bit less complicated. You're still pushing air down instead of up, but it should still prime the system and get most of the air out.

Combine that with elevating the calipers and you probably have a pretty good setup.

And because of the remote master on the z1r, you could do all of the bleeding process with the parts off the bike away from the paint.

Ok so we bought a vacuum bleeder kit and managed to suck fluid down through the brake lines and the master, but now we've run into a different problem. We tried both letting it sit for two days and clamping the brake lever to the handlebar but neither helped. Once we got fluid through the lines we then proceeded to bleed the brakes as usual, the old school way, until no more air bubbles are left in the fluid. However, the brake lever refuses to "firm up" and the brakes do not function. Any thoughts as to why this might happen?

My first thought when you say it won't firm up is that there is still air trapped in the system somewhere. As you go through the bleeding process does the brake lever begin to develop resistance or does it always seem to have the same amount of lever effort? Are you absolutely sure your master cylinder is pushing fluid towards the caliper? Every now and then you can run into a brake system that must be bleed over and over again to get all the air out. Multiple calipers can be quite problematic. I would continue to bleed the system and see what happens. Remember too to never allow the brake fluid to get too low in the reservoir while bleeding the system or your are back to square one.
Rick H..

The brake lever maintains the same low level of resistance throughout the process, and I would say that we've bled the brakes five times now, but we will continue to try. The master is definitely pushing fluid as some comes out every time we pull the lever while bleeding.

Do you have a brake bleeding apparatus hooked up to the caliper bleeder? so that air won't get sucked back into the system. this is why speed bleeders are handy >> fluid only goes one way thru the bleeder & air can't enter the system there.

Yes we use a mini bleeder from Motion Pro it looks like this.
Mini Bleeder

never mind. I now see that it has a check valve.
It might help to watch some brake bleeding videos on youtube.