KZ400 Caliper / fork swap tutorial

I recently competed this swap and figured I would write up a tutorial as it seems to be a reoccurring problem for 400 owners not being able to get a caliper rebuild kit. I owe a big thanks to Nebr_Rex here for giving me details on this swap.

Here is what you need;
KZ400 wheel
KZ400 disk
KZ400 triple clamps
81-83 KZ440 axle with spacer
81-83 KZ440 forks
KZ440 caliper (or lefthand from kz1000, kz650, kz750. assembly number is 43041-1024 if you want to look up models that used it)
14mm Master cylinder

If you do not have access to a mill or lathe you need to make friends with a machinist

First, turn the 440 axle spacer down to 1.114"


Remove .135" from the right fork bottom, where the speedo sits. This will roughly center the wheel in the forks.
Remove .23" from the left fork caliper bosses





This is all that is needed to run the 440 disk. However the 440 forks are 2 1/16th longer than the 400 forks. They are easy to shorten.



Cut two 2.0625" tubes. I used 3/4"OD .065" wall mild steel. I have heard of people using PVC but i like metal. insert this spacer under the return spring on the dampener rod.



Cut of 1.75" off the fork springs. make sure to cut the big end not the small end. This will add some preload to the fork, since im a big guy and i thought the forks were a little soft I did this. you can still get the cap and retaining clip in easily.
Reassemble forks as normal using the 145-155ml of fork oil as per the FSM. While you're at it put in some fork seals. (the 440 is on the left, 400 on the right)



The fender mounts are different on the 440 forks. I used one of the existing holes in the 400 fender mount, drilled another hole, and trimmed the excess. This mounts the fender much closer the tire, i thought the stock position was too high anyway. I also cut and drilled the fender struts to match.



Thats all there is too it. Hopefully this helps someone when they are looking for a solution for their 400 brake.

This will not work exactly as described for the 78-79 KZ750 B this particular model and years have a 17mm axle.

I was the lucky one with the 78 KZ400 B1 that tried this swap. DoctoRot asked me to get a write up going if I could get this sorted. And well no doubt we got ourselves a workaround.

Just as before a mill lathe is gonna be handy. I had to make my own axle spacer, but potentially something similar could be found, modified ...

What you are going to need:
78' KZ400
Wheel
Disk
Right Fork
Axle
Speedo

80 - 83 KZ440
Left Fork or just the Boot
Caliper

The game plan:
1. Create a custom axle spacer.
Thickness: 0.08"
Outside Diameter (OD): 1.265"
Inside Diameter (ID): 0.670"
2. Modify and swap only the left fork boot which contains the caliper bosses.
a. Open the axle diameter to 17mm
b. Mill down caliper bosses by 0.36" and clear out the side of the boss for the caliper mounting plate
c. Mill down the fender mounting bosses by 0.10"
d. Grind down the speedo stop
3. File, mill, or grind down the caliper mounting plate to allow clearance for mounting

So as soon as I got my KZ440 forks I realized the axle diam. was too small. So I thought open them both up, use the original axle and call it a day. But unfortunately the axles are different. The 78' KZ400 has axle pinch bolts on its right fork while the 80' KZ440 is a solid axle mount. And of course then the axle bolts themselves are different to accommodate these two axle mounting styles. The pinch bolts help you to align your axle with the forks to prevent binding, which sounds like a better axle to me. Dunno why the early 80s 440 uses that flush style. Would love to hear any opinions on pros/cons.


The KZ400 axle will tighten everything against your left fork and then the right fork would pinch the collar of the axle. This allows you to have some error with your axle spacers which wont bind your forks if your wheel is not perfectly centered. To me it seems like the 440 axle would bind the forks if your collars are too big or too small because it clamps both forks against your wheel hub, bearings, and spacers.

So first thing first take apart your KZ440 fork and grab just the fork boot, the rest of the parts can go in your spares bin, the spring is different tho so watch out. While you're at it and fresh at breaking open old rusty forks go ahead and take your original KZ400 left fork apart. Discard the left KZ400 fork boot and keep everything else (spring, damper, tube, damper cover, and the little spring… EVERYTHING)

1. The thickness is easy to figure out by comparing the two forks. You'll see the only difference is that the critical wheel facing side is a little smaller, get the difference and lets roll. The spacer should be 0.08" thick.


To make the spacer I took a square piece of steel drilled a hole in the middle to the ID (inside diameter) of the collar then turned it on a lathe to the OD. To get the thickness I used a surface grinder. The material does not have to be steel, aluminum should work fine and be easier to cut. If this fabrication is too much maybe a washer(s) or something could work?


To roughly center the original disk in the caliper I took off around 0.36" +/- 0.01 wont hurt any (mine was a little over 0.35").

a. Use a 17mm reamer or cutter, a little over should not be a problem. Mine was under and I had to jam feeler stock in with the reamer to get my dimension.

b. The amount to mill on the caliper mounting bosses should be 0.36" which for me was the thickness of the caliper mounting plate. I just kinda held it up to the bike with the 440 boot in there and eyeballed it. Looked like the face of the 440's caliper mounting bosses lined up the with the face of the caliper mounting plate.

Luckily my vice already had holes that lined up. But its really easy to drill and tap holes in your vice if you can stomach it (noo my precious vice noo) or figure out another mounting method. I used a counter bore with a replaceable pilot which I turned down to just fit the ID of the boss making the alignment easy and accurate. For the diameter of the counterbore cutter I found something close to the OD of the caliper mounting boss. A little over is okay, but def nothing smaller. The last thing here is the mounting plate clearance. After you finish your depth cut take out the counterbore pilot and clear out the top of the boss towards the inside of mounting plate. I was rushing and forgot to take out the pilot on my second cut breaking it off in the mounting hole. You can see the difference, luckily for me I got away without any show stopping damage.


c. Mill down your fender mounts by 0.10"
d. Grind off a little bit of the speedo stop so it doesn’t hit the speedo.

The last thing is just to take a touch off the caliper mounting plate to make it flush at the top mounting hole which will hit the inside of the caliper's top mounting boss on the fork boot.


Okay now its time for the fun part. Reassemble the left fork using the modified fork boot from the KZ440 and all the original guts, springs, dampers, tubes, caps, spacers from your KZ400 fork. This will ensure the heights and everything else will be stock with the forks except for of course the left fork boot. Mount your front axel as you would before and slip on the custom spacer between the boot and speedo. Tighten up the axle, mount the caliper, and bask in the glory of a job well done.


I went ahead and junked the original caliper, got a used 2013 Ninja 300 caliper from ebay for cheap. Got rid of the hydraulic brake light pressure switch and put in a steel braided line. And of course moved the wires over from the pressure switch to the micro switch on the new caliper.

Hopefully no one ever has to do this, but if you do and have any questions feel free to hit me up.
Maybe the next upgrade will be to a dual disk with the next model (mid 80s) caliper.

Want to give a shout out and big thank you to DoctoRot for getting his guide together and getting me going on this. THANKS!

Hi all, recently inherited my fathers 1978 kz400 and attempting to get it to a ride able state.
Front caliper seems to be the major problem this far.

Is there any way around all grinding and milling from your write ups?
For instance, using forks/wheel/axle off an 80-83?
or am I sol?

Thanks to Vic and Fiddles for this write up.

Last I checked, a couple months ago, someone is now selling a brand new main seal for the Kz400 caliper on Ebay, but it seems suspect to me. It's super expensive and he claims it will fit even though it "looks different", whatever that means. I didn't take a chance on it. I just rebuilt the caliper with old parts and prayed it wouldn't leak. So far it's been ok.

Doing a complete front end swap is a possibility but you will need to lower the forks even more because the 440 has a 19" front wheel. If you dont care about a "stock" look you can adapt a different caliper to fit but this will likely create a need for machining as well.

Thanks for the tips everyone, this forum is a godsend for this old bike.

I'm still weighing my options. trying to decide between attempting Fiddles write up of swapping a 440 fork boot or run with the original caliper and bite the bullet on the ebay piston seal.
I've searched and searched, but these seem to be my only options.
I don't suppose the A2 or earlier year calipers are a direct swap for this bike either?

I know I'm going to need a new caliper either way, the caliper mount/swivel on mine is pretty well sized; don't think I'm getting it out without a press(or major damage to it).

I am attempting to keep the bike mostly stock, but would rather have a brake I know I can get parts for in the future.

loudhvx wrote: Last I checked, a couple months ago, someone is now selling a brand new main seal for the Kz400 caliper on Ebay, but it seems suspect to me. It's super expensive and he claims it will fit even though it "looks different", whatever that means.

I took a chance on the seal back in '17 but it started seeping on me recently. I contacted Lee (junkboy66 on eBay) and he is sending me a new one so he does stand behind his product. Maybe I got one of the earlier ones. My 400 is rarely ridden but I do like to keep it rideable. I'm not looking for maximum brake performance so YMMV.

ThatGPzGuy wrote:

loudhvx wrote: Last I checked, a couple months ago, someone is now selling a brand new main seal for the Kz400 caliper on Ebay, but it seems suspect to me. It's super expensive and he claims it will fit even though it "looks different", whatever that means.

I took a chance on the seal back in '17 but it started seeping on me recently. I contacted Lee (junkboy66 on eBay) and he is sending me a new one so he does stand behind his product. Maybe I got one of the earlier ones. My 400 is rarely ridden but I do like to keep it rideable. I'm not looking for maximum brake performance so YMMV.

thanks for the update. I may give it a try if this old seal starts leaking.

The new seal is holding so far.

I am about to try this swap but….. I have a bit of a different approach path. My kZ440 is a 80 B model. So it has the drum brake wire wheels 18 inch and the left fork leg has the mounting points for a single caliper. My question is this I noticed that the axle looks like on the 400 it clamps to the lower for leg on the left side while my clamp point is on the right. I am hoping that it all works out as I just jumped on a mint condition wheel that came with axle spacers and all the bits needed. I just had to get a master cylinder and the caliper. I hope someone has tried this and can say for sure if it will work but if not I will update the thread with pics as I fiddle along with it to get it fitted to the bike. I also want to say thanks to all the people who have contributed on this site it truly is a super group and has helped on this and my kz250 ltd project. I will share a couple pics the 440 is a complete tear down rebuild and the 250 was a barn find I freshened up. 

I'm wondering if anybody has found bigger rotors/calipers from other bikes that can be adapted to the stock wheel?  I'm very new to the site but I haven't found posts about it.  My son had a mid-70's Honda twin that I did this to...mated a 298mm rotor from a Yamaha Vmax to the stock carrier on the Honda & a twin piston sliding pin caliper from a Fury.