Front fork and Breaks Z 750-S1 Twin - 83 vs Z 750E -81

Hi
Working on a project to build a Bratbike/Flat track on a Z750-S1 from 1983. When I bought it, I got a chassi incl spokes, tires, breaks and forks from a Z 750E (80 or81).
Decided to replace those funtioning part since they where in better chapes and to upgrade to disc brake back instead of the drum break.

Some questions to above adjustments:
1. I kept the trippel head from the S1, but replaced the fork, breaks and wheel. Have a feeling that the with of the trippel head and the wheel might differ 1-2 mm (wider at the top). Planning to add some chim trays at the wheel axel to compensate this.
2. Are the break pads same front and back? Only had old pads for the front breaks but the desing and functions looks very similar.
3. Air-pressure front fork. At the moment the frontfork is veyr swampy. Planning to change the oil but first of all fill it with air to make sure they are not leaking. Guess I have to thread some kind of valve at the top. Can I do this with a compressot and what dimension/adapter would be needed?

Anything else to chekc or keep in mind to avoid any misstakes?

Howdy. Do you have the Kawasaki factory service manual that covers your 750-S1?
That model wasn't sold in the USA & most places won't have diagrams to compare the parts.
So you'll probably have to use the manual, EB pics & your eyeballs to figure if your components are the same as the 750E or any of the 750Twins, then figure out what might be swappable.

I'd guess the 82 KZ750-M1 CSR & 83-84 750-K1/K2 models would be the best matches. just guessing.
From your avatar pic the muffler stay looks the same as what those models would have, so other parts might be the same as well.
However as for the brakes, the M1 & K1/K2 had a single disk Fr brake & Rr drum brake (not dual disk front. not rear disk brake).

The brakes, if from the KZ750E, should have similar pads front and back, but the model numbers are likely different. This is due to different pad thickness for the different thickness discs. Some aftermarket pad manufacturers will sell pads that fit both front and back by just normalizing the pad thickness. But really, if you take the pads from the front and they fit on the back, then they're the same. Just make sure that any new pads aren't too thick. I know that not all E models have the same brakes, so it's possible that not all of them will work.

If your front forks are air forks, my suggestion would be to ignore the air-fork gimmick. I stuck with it for a while, I liked the idea, but really they're just not very good. The increased pressure causes the seals to grab on the stanchions and results in a sticky travel.

After decades, the springs get a bit tired and people try to make up for the sagging suspension by putting in more air. My advice would be to not pressurise the system, but to use a thicker oil (15W instead of 10W), and fit a spacer (or longer spacer if one exists) to increase the preload. Add just enough preload to get the sag to the right level. If this doesn't get your forks to a level where you like them, the next step is to look at new springs and potentially cartridge emulators.

Hi
Very usefull information. Thanks for sharing!

/johan