Master Cylinder 1/2 inch on dual disks

I have a 81 KZ1000J. Will the master cylinder from a 81 KZ550 looks the same but is(1/2 inch) work on my 81 KZ1000 which calls for the 5/8 size. This number is stamped on the bottom on the master cylinder. I believe its the piston diameter. Thanks.

As long as it mounts onto your handlebars, yes you can use it.

It's pretty much a 50% split amongst the members here on whether the 1/2" bore or 5/8" bore gives a firmer feeling/better performing brake on a dual-disc set up though. :S

82KZ1000LTD wrote:

I have a 81 KZ1000J. Will the master cylinder from a 81 KZ550 looks the same but is(1/2 inch) work on my 81 KZ1000 which calls for the 5/8 size. This number is stamped on the bottom on the master cylinder. I believe its the piston diameter. Thanks.

You are correct about m/c size being measurement of piston diameter.

Same linear movement of larger piston pushes more fluid. When Kawaski first offered the optional second front disc on 1976 KZ900 USA models, the factory kit included the larger 5/8" master cylinder along with the other necessary parts (as came standard on the KZ900 European models).

Believe 1/2" inch bore m/c on single disc KZ900 was increased to 5/8" for dual discs to allow additional volume for operating second caliper. Probably 5/8" would be okay for single disc (with less lever movement needed to brake) but 1/2" may not push enough volume to safely and consistently operate two calipers. Lever may possibly pull against the handlebar grip before pads sufficiently grip the discs. Might be okay with an otherwise perfect brake system with fresh fluid and completely bled, so long as there's a good hard (not mushy) lever feel with a margin of unused extra movement space available before hitting the handlebar grip.

With that said, am guessing there are many KZ900's pushing dual front calipers with 1/2" front master cylinders. Best wishes and good luck to them.

IMO brakes are too important to take even small chances with or second guess Ma Kaw engineers, so in abundance of caution I would recommend not using the 1/2" master cylinder in place of a 5/8" m/c for use with dual calipers on KZ1000.

If the OEM '81 KZ550 pushes dual calipers with a 1/2" m/c, good for it, but the OEM KZ1000 pushes dual calipers with 5/8" m/c, and I'm unfamiliar with the different engineering involved between them.

Happy Trails.

Patton,
As I recall the whole bru-ha-ha back when it happened (some of us were alive and paying attention back then) it was not a question of capacity, but of mechanical advantage. Riders found that it didn't take very much effort to lock up the front brakes. Racers loved it, newbies killed themselves. Kaw went conservative (and wisely so) and opted for a master cylinder that took much more effort to lock up the front wheel. But I don't remember anybody having a capacity problem.
So, 82KZ, be forwarned: the brake effort will be dramatically reduced, and in a panic situation, lock-up is likely. If you're confident in your ability to master this (yes, pun intended) go for it.

And the old wound is opened up yet again...:pinch:

My European Kz 500 B2 has twin front disks and uses a 5/8 inch master cylinder bore. The B1, which appeared in 1979 had a single disk and used a 1/2 inch bore.
Kawasaki made this change in the space of months because they had so many complaints from B1 riders of "inadequate braking".
Fully laden,[with me on it]my bike weighs 286 kg.
The thought of a 1/2 inch bore on a bigger capacity,heavier machine would be enough for me to question even sitting on it!
Even though it's undeniably "thrilling" to wonder in terror if the bloody things gonna stop in time, at my age,[and most of you I suspect],it's rather more important to know that a Kz with effective brakes won't give that heart stopping fear that the twin leading shoe joke on an early two stroke was furnished with.As evidenced by my head marks on the local church wall.:woohoo: Conclusion:don't take the chance.

Hydraulics 101 in a nutshell.

Assuming equal hand squeeze pressure on both 1/2" and 5/8" master cylinder levers:

5/8" lever will not travel as far as 1/2", and will take longer to stop.

1/2" lever will travel farther than 5/8" lever, but will exert more pressure on the pads, and stop quicker, assuming you have enough room to allow the longer lever travel.

Some KZ models had 5/8" master cylinders on single disc brakes while others had 1/2", I am not aware of any stock dual disc KZ that used a 1/2" master cylinder, but there may have been some.

read the article in the filebase about the dual disc upgrade. it talks about using both 1/2 and 5/8 MCs

pstrbrc wrote:

So, 82KZ, be forwarned: the brake effort will be dramatically reduced, and in a panic situation, lock-up is likely.

I can second that. My 77 650 is running dual discs off a Z1R with the stock 1/2" mc and braided lines - it brakes really good, in fact so good that I managed to lock up the front wheel twice in a couple of tight spots and went down on both occasions. Different strokes for different folks, but the 1/2" mc is being replaced with a 5/8" as soon as I can find a master with integrated brake light switch for a reasonable price.

use less fingers on the brake!!

77KZ650 wrote:

read the article in the filebase about the dual disc upgrade. it talks about using both 1/2 and 5/8 MCs

Have a link for this? Am somehow missing the article in filebase, and attempts with archive search results in error message. Thanks.

Dual disk conversion