Front Brake Components

When doing the brake, did you use a brake bleeder apparatus >> usually clear tubing connected to the bleeder nipple & the other end of the tubing immersed in a clear container of clean brake fluid? It sounds to me like there's still air in the system.

A speed bleeder pretty much eliminates any chance of air entering the system, but I still connect tubing w a jar of brake fluid so that I can see the air bubbles exiting.

Another thing you can do is unbolt the caliper, shim the brake pads so they can't move, then position the caliper so that the bleeder is angled upwards. you could also elevate the caliper so that the air bubbles can more easily exit the system.

For starters you have the wrong size master cylinder for your bike. The picture shows a single front disk, but the image you posted shows that the master cylinder piston bore is 16mm. The stock KZ650 dual front disk brake system is 5/8" which equals 15.875mm. So you have installed a master cylinder that is appropriate for a dual disk system on a bike that has a single disk system - not a good idea. Aside from that you may still have air in the lines, but even if the lines are bled completely of any air the master cylinder is still wrong size for a single disk brake system. Ed

By 650ed: For starters you have the wrong size master cylinder for your bike....

That, plus assuming it's made in china, who knows what the quality is. I avoid chinese junk whenever possible & this is one of those opportunities. I went with a good used Honda part. It's the Nissin brand found on many Japanese motorcycles. plus spare parts are available >> I installed a new Honda brake lever with it.

Typically a 14mm master is used on single disk brake bikes. Using a 16mm master will work but more lever force will be required for the same braking force generated. A 16mm master will also make the lever feel MORE FIRM. Since the hand lever is feeling mushy that either means air is in the system or the caliper pistons are not moving close enough to the disc. The "tie the hand lever to the bar" trick is to get the caliper pistons to creep out over time and move closer to the discs. I'd bleed once more and then try tying the lever back overnight.

It goes without saying that a 40 year old bike should have the caliper torn down, cleaned out, and corroded parts replaced. Also replace the brake line since it's sure to be full of scale after so many years. Time and money well spent, particularly if the caliper pistons are binding.

650ed wrote: For starters you have the wrong size master cylinder for your bike. The picture shows a single front disk, but the image you posted shows that the master cylinder piston bore is 16mm. The stock KZ650 dual front disk brake system is 5/8" which equals 15.875mm. So you have installed a master cylinder that is appropriate for a dual disk system on a bike that has a single disk system - not a good idea. Aside from that you may still have air in the lines, but even if the lines are bled completely of any air the master cylinder is still wrong size for a single disk brake system. Ed

Thanks for the info. Could you please send me a link to a good replacement mc assembly? I don't know what good bad, right or wrong. Lol. I'm a little out of my element.

Dont pump the brakes when bleeding. Fill the reservoir, open the bleeder, pull lever, close bleeder, release lever, repeat. This moves alot more fluid and keeps it going in one direction.

A speed bleeder makes the job simple. no opening & closing the bleeder over n over. just open it to start the job & close it when done. and you can pump all you want. I will never do the job without a speed bleeder ever again.

martin_csr wrote: A speed bleeder makes the job so simple. no opening & closing bleeder over n over. just open it to start the job & close it when done. and you can pump all you want. I will never do the job without a speed bleeder ever again.

+1 !!! Ed

Thank you Martin_csr. I had seen the speed bleeders but wasn’t sure if they were just another sales gimmick. I’m detailing the rear swing arm on my 1978 1000 LTD, replacing the rear brake line in the process of making it look pretty. MC was rebuilt recently. Thanks again for the unsolicited product review, and 650ed for seconding the positive review. I’ve places an order for the speed bleeders.

I just want to say thank you to everyone how shared their advice and experiences. I just made an order that will hopfuly put this thread to rest. I ordered a Nissin master cylinder. 7/8 Handel bars. 1/2" piston and a 10x1.25mm banjo bolt. All within specs. Hopefully this works and I can finally get out and ride. Also. To whoever said be careful of Chinese parts..... The clamp broke when I was reattaching it to the Handel bars.. Thank God I wasnt riding it when it broke. Anyway I'll leave a link to the site where I got it. Thanks again everyone for everything. Learned lots of stuff from this post!

www.dimecitycycles.com/vintage-caferacer...linder-717-654h.html

By Jpallison1722: .... Also. To whoever said be careful of Chinese parts..... The clamp broke when I was reattaching it to the Handel bars.

Holy crap. That was me & I thought I was just being a worry-wort, china basher. I've heard of the cheap chinese shocks breaking, but this is the first time for a master cylinder. dang. glad you weren't riding at the time.

Yeah me too lol. I've have plenty of parts made from Chinese mystery metal break on me so it's really my fault for buying it. This is what happens when you cheap out of things lol. Thanks for the heads up I've been thinking about it ever since reading the comment.