1983 KZ750 L3. Really Struggling For Brakes

As I have noted in other posts I am putting my 1983 KZ750 L3 back on the road.

Things are going pretty well. But I am REALLY struggling to get any front brakes in it.

Calipers cleaned up by a known good Kawi mechanic.

New braided lines to the front block then old line to the master.

New eBay top/front master.

Does not seem to be sucking or leaking from anywhere but it will NOT build any lever pressure at all.

I am beginning to wonder ... I am confident that the calipers are good, the connections are good.

Thinking about buying a new front master and lines all the way to the master (two lines going straight to the master) with a new banjo on the master.

Pretty much my supply house is eBay. Can anyone recommend a good seller there for KZ braided lines, masters and the like?

Try reverse bleeding: just lift the reservoir top off and 'gently' squeeze the lever - you'll see bubbles rising up. Do this a few times, then bounce around on the forks and lean it side to side -you are trying to get the bubbles to float to the top.

Briaded steel definitely improves the feel -but assuming they have been rebuilt properly and it isnt MC or caliper seals your issue is air in the system.

WARNING cover the tank, frame and instrument glass, brake fluid will ruin eerything.

Put a long piece of clear tubing on one of the caliper bleed nipples, open the nipple, and then suck on the line to pull fluid out of the master. Draw the fluid all the way though the system. Typically once the master pump chamber gets filled with fluid the master will then start to pump after that.

This is what I use when doing brakes, slacken off the bleed nipple and inject in some brake fluid. You can buy them from flea-bay.

Thanks for the assistance.

Typically what are you guys running for a replacement master cylinder. I think I am using a China version of a model for the Yamaha FZR600. Perhaps this is the issue as well?

You need to size the replacement MC to the calipers: 1/2 " or 5/8" from memory. Getting it wrong will give you either really 'grabby' brakes or too much lever travel...not your problem here.

I have been known to remove the caliper, put a bit of wood between the pads and bleed it - tapping the caliper and pointing the bleed nipple right at the top to allow bubbles to rise.

70's 80's kawasaki are 'metric' bikes but some components are imperial measurements for economy of sourcing parts at the time.

If you are getting zero resistance at the lever the master is not pumping. You need to get some fluid into the master bore, the pumping chamber so to speak. Once you get that flow started by "priming" the system the master will pump fluid downstream allowing you to bleed the system per normal.

For dual disc bikes like the L3 you want a 5/8" bore master. Some guys use a 1/2" bore master which will work too, only the hand lever will feel spongy, almost as if there is still air in the system, even after the system is fully bleed.

This is almost definitely the trouble, and it is a pain in the neck sometimes. Odds are you have a big fat air pocket at or near the master cylinder and although fluid will pass it, it won't force it down. Here are some strategies for getting them bled.

First off, protect your tank and bodywork with a blanket. Next, rotate the bars, and the MC on the bars so it's at the highest position, and most preferrably with the top banjo bolt angled down from the MC and reservoir above. Level the reservoir, open it up, remove the cap and diaphragm. If it's super full you may want to suck some fluid out with a turkey baster.

Next, fan the brake lever a few times, as fast as you can, WHAP WHAP WHAP! Don't be gentle, We're trying to dislodge an air pocket with this move! Watch the reservoir and see if you get a telltale big fat bubble to rise up. Repeat this a few times.

Next, hold the brake lever about halfway back and take a small plastic hammer, and tap tap tap on the MC just above the banjo, and again, watch the reservoir and see if you're making headway. Get some teeny bubbles? KEEP TAPPING. Take a break, go down to the calipers and splitters, and tap your way up, bottom to top, same thing we are trying to dislodge bubbles, repeat the tap at the MC.

Next, take the night off! Pull the brake lever halfway back to the bars, strap it in position like that and replace the cap on the MC, but not the diaphragm. Give it all one last good night tap and let it sit overnight like that. Check in the AM, lather, rinse, repeat. When you're happy with it, replace that diaphragm and cap, top off the fluid.

Short version is that sometimes there is no amount of fluid or suction you can draw from the bottom to draw down a bubble at the top, you need to create a path and the motivation to dislodge it to rise up to the reservoir in that direction instead.

Report back!

N.

I have 1983 KZ750 L3. Spongy front brake . Rebuilt front calipers. Tried 2 new master cylinders. Bled:. With: lever pump method, vacuum bleed, reverse bleed, reverse pressure bleed,. Tape lever to handle ( several times, sometimes not just over night -- sometimes for a week or more). Gravity bleed with calipers hanging, pads taped in place. Notice that with calipers hanging free, they rotate slightly when lever squeezed. I think brake hoses might be soft...

misterdgc wrote: I have 1983 KZ750 L3. Spongy front brake . Rebuilt front calipers. Tried 2 new master cylinders. Bled:. With: lever pump method, vacuum bleed, reverse bleed, reverse pressure bleed,. Tape lever to handle ( several times, sometimes not just over night -- sometimes for a week or more). Gravity bleed with calipers hanging, pads taped in place. Notice that with calipers hanging free, they rotate slightly when lever squeezed. I think brake hoses might be soft...

What is the bore size of the master? 5/8" or 16mm hopefully. If using a 14mm master the lever will feel spongy. If you used aftermarket seals in the calipers, particularly K&L, that may be contributing. I've seen this same problem from K&L seals several times before. Last thought is to change the brake lines. Reusing old brake lines is like reusing a condom. Not good. The old lines are sure to be full of crud which will contaminate your new brake fluid.

Since my message 2.5 years ago we purchased a MityVac air operated brake bleeder. Harbor Freight sells something similar. Using one of those, one man can fill a three line brake setup in about 10 minutes, strap the lever to the bar overnight, and that's that. If you work on these things with any frequency, quit messing with this and sacrificing chickens and get thee one.

Thanks for help!!
Ordered 5/8 bore m cylinder
Going to order new brake lines, measuring lines for precise length ( centerline of banjo bolt to banjo bolt). Seems like some places only go to 1979 model year for kz750....
PS I did use K&L seals... Still have old seals. Maybe put them back in later if m cylinder and lines don't help... Thanks again!