front caliper rebuild

Hello everyone,

I am working on my 78 KZ400B1 and after replacing the master cylinder and bleeding the brakes I have realized that the caliper needs to be rebuilt.

Basically the seal is not pulling the piston back so the front wheel does not spin freely. There is a lot of friction.

Rebuilding them doesn't seem to be much of an issue, the problem I am encountering is I cannot find the necessary parts. I ordered them from cycleparts but they called back to say that they were discontinued. So my question is does anyone know of someplace that has the parts or should I just look at replacing it with a different caliper. Anyone have suggestions or experience with this? Maybe some ideas on calipers that will fit and of those which ones have service parts readily available.

I was thinking of going with a KZ440 caliper as I did find a place that sells a few rebuild kits for various 440 models.

Thanks, Stephen

Have you looked at the seal? I haven't done a Kaw caliper, but I've done several H^&@a's and those seals rarely go bad, unless you have some oil contamination. If oil gets in there, you'll get swelling of the seal and then it's junk.

Most times cleaning the groove that holds the seal will do the trick. Grunge gets built up in there and cause the seal to tighten around the piston.

Is the tiny relief port in the master cylinder allowing the brakeline pressure to relax when the lever in longer being squeezed. In other words, is there still some brakeline pressure to the caliper when the lever is released (not supposed to be) thereby disallowing the caliper piston to fully retract.

Could test by pumping brake to firm pressure. Then release the lever. Then open the bleeder screw, which should not shoot out any fluid because the line should no longer be under any pressure. If fluid shoots out the bleeder screw when the hand lever is not being squeezed, something is wrongfully allowing pressure to remain inside the line.

If the caliper piston isn't fully retracting dispite no pressure in the line after releasing the hand lever, perhaps the caliper piston and/or its chamber has some corrosion which is preventing free movement back and forth inside the chamber and requiring more return force than the caliper piston seal can provide.

Good Luck!

Well the master cylinder is new, so I do not think the issue has to do with the relief valve.

I also removed the caliper and even with the bleeder open I had to use a clamp to move the piston.

If it is badly corroded is it safe to clean it with ultra-fine steel wool or something. I don't want to do anything that makes the brakes unsafe.

Thanks,
Stephen

steveed wrote:

Well the master cylinder is new, so I do not think the issue has to do with the relief valve.

I also removed the caliper and even with the bleeder open I had to use a clamp to move the piston.

If it is badly corroded is it safe to clean it with ultra-fine steel wool or something. I don't want to do anything that makes the brakes unsafe.

Thanks,
Stephen

Hoping the usual method of using normal brakeline fluid pressure to push the caliper piston out of its chamber will work okay in this instance, so as to avoid damaging surface of the piston by gripping it with a tool (clamp?) of some kind. If not, other methods are available such as compressed air, grease gun, etc. to avoid having to risk damaging the piston surface by gripping it with some sort of steel tool.

Once removed, it may be perfectly all right to clean up the piston (remove rust and corrosion) with fine steel wool or otherwise. Same for inside the chamber. The main idea would be a smooth enough piston surface resulting whereby the seal would not allow fluid under pressure to leak between it and the piston.

I looked on Kawasaki.com which unfortunately shows this particular caliper, piston and seal being applicable only to a few KZ400 models. Perhaps someone else may know of another model's seal which would fit, or another source. Is it no longer available from a Kawasaki dealer? As I recall, these are fairly expensive due to supposedly special heat resistant rubber being used.

Not suggesting this, but am wondering if the piston O.D. is same as some other model, why wouldn't the same seal work so long as it fit snugly inside the caliper channel. Must be a variance in the seal O.D., thickness, or otherwise. Am surprised to learn that all the different calipers use their own special seal unique to each particular model's caliper.

Good Luck!

Well I took the caliper apart and cleaned it out, overall it didn't seem very dirty and after reassembly the piston slides a bit better but still not very well. I can now get the front tire to make about half a revolution as opposed to a quarter before.

I read on another forum about using brake grease on the seals, not sure if this will work correctly because the seal is supposed to be pulling the piston back. Has anyone tried this before?

The caliper holder is also not in the best shape it seems to be quite rusted and I was unable to take it apart though I did get it to spin.

I think I am going to look for a replacement caliper.



As far as the clamp I didn't "grip" the cylinder with it I simply used it to push the piston back into the caliper much in the same way the shop manual shows the use of a press. Since this is what the manual shows I am hopeful it didn't cause any damage.