1980 750 twin brake upgrade questions

presently resurrecting a barn find 1980 KZ750G.

would like to upgrade where possible (and not too expensive).

one upgrade opportunity is front brake. stock fork tube has mount for 2nd caliper:

1. can a right side disc and caliper from a similar vintage KZ (like the 750 or 1000) be mounted on the 750 without modification?

2. will the stock front mas cyl work with the dual caliper upgrade?

3. is there another alternative like a fork/brake assy from a much newer bike that would fit without significant mods to the 750's frame or the upgrage fork assy? (I would spend a few hundred to get significantly better brakes.)

thx in advance for help or suggestions.

Mark in MN

Master cylinders for single disk brakes have a 14mm bore. Master cylinders for dual disk brakes have a 5/8" bore. If you switch to dual disks you need to change the master cylinder if you want decent braking. Ed

Steell (a member here) has just the info you are looking for.
kz750twins.com/?p=131
All of these parts can be found on ebay or z1enterprises.

650ed wrote: Master cylinders for single disk brakes have a 14mm bore. Master cylinders for dual disk brakes have a 5/8" bore. If you switch to dual disks you need to change the master cylinder if you want decent braking. Ed

Theres plenty of bikes out there that have been running the smaller master cylinder for years with dual discs,its a matter of preference.

You mean like this one?
(A previous incarnation of my current bike)

So you guys have personal experience with using the 14mm master cylinders with a dual disc set up? I'm in the process of converting my '78 A model and have been torn on whether or not I need to change from the 14mm m/c to the 5/8" m/c. Think the 14mm would be OK?

The 14mm mastercylinder will be very touchy. You will have the best feel if you use the larger mastercylinder.

80B4 wrote: The 14mm mastercylinder will be very touchy. You will have the best feel if you use the larger mastercylinder.

+1 ! Also, if you use a 14mm with dual disks the lever will need to travel further to push enough fluid for 2 calipers. The different bore sizes in the brake systems used by Kawasaki and other bike manufacturers were engineered for performance - not looks or cost savings, so there really was a reason for the different bore sizes. Assuming you are upgrading your brakes to a dual disk setup it makes sense to me to employ the same master cylinder size specified by the engineers.

Here's a cut & paste from another site you may find interesting. This KZ650 owner tried a 14mm master cylinder with dual disks and came up with what I consider to be a rather conclusive test.

"I thought I was going crazy not being able to get a decent lever feel no matter how I bled the brakes. Done the reverse bleed and absolutely no air bubbles coming up to the master. I then started to wonder if it really could be the dreaded 14mm vs 5/8" issue so started clamping down hoses to see if reducing the volume allows the master to operate at its sweet spot. Before starting the lever could easily pull all the way to the bars. Clamped the single line from master to splitter and the lever was rock solid. Moved only about 15 mm from the resting point. Released it and back to the full travel with mushy feel. Then clamped the left caliper hose and this time the lever comes in about 25 mm and is pretty firm. At that point I thought I may have air in that caliper but swapping the clamp to the right side hose has the same effect, a near perfect feel with 25mm of travel before brake is fully on.

This leads me to believe that the m/c simply cannot move enough fluid to operate the brakes through these hoses, splitter and dual calipers."

Consider that when Kawasaki offered the factory kit to convert single disc Z1 front brake to dual discs, the kit included a 5/8" master cylinder to replace the stock 14mm master cylinder.

Good Fortune!