I think that doing a simple test should isolate your problem. I mentioned it in my post above-when the lever gets soft pump and hold pressure on the brake lever. While applying pressure open the bleeder on the caliper-if you get bubbles then it's possible that the caliper seals are allowing air to enter the housing. If you get no bubbles then I'd be almost 100% sure that the m/c is sucking air past the piston seal.
Do the diagnostic work and it will point you in the right direction.

 

Hi GBAUTO, I understand completely what you meant in your first post. I just bled the fluid last Friday and checked for bubbles. There were none coming from the bleeders. There were some very small bubbles coming out of the MC into the reservoir. That pints to the MC as you said right?

 

As far as pulling air into the system, as GBAUTO suggests the caliper piston sealing rings are the most likely if you've insured there are no fittings that aren't leaking...which you should be able to see from fluid residue. The caliper piston sealing rings are the largest sealing component in contact with the fluid, and they're in the nastiest environment. You'll usually see some fluid residue when this happens, but again, not necessarily always.

On the All ***** MC kit, I'm not a fan of their stuff. I haven't heard anything on their brake parts, but we've had bad luck with their fork seals around my home area. I had fork seals fail in just weeks, and the head seal in my rear shock didn't last a month. I know how to install those parts. My friend who runs the parts department at the shop I used to work at part time said some of their bearing kits seemed to be fine, but there have been more than the normal instances of problems with their rubber/seal parts. I have no idea about their brake parts kit. It's also common practice to go back to the last thing you repaired or serviced on a vehicle when a problem arises.

 

Good info TNC, I'll look for fluid residue when I rebuild everything this weekend. Anything else I should look for in the calipers? Last time I rebuilt them I saw no scoring or pitting.

 

If there were no signs of bubbles coming out of the caliper bleeder when you had a soft lever then I would say that the issue is with the m/c. Take the m/c apart and inspect the bore closely for signs of pitting. If that looks good then order a new piston from Kawasaki p/n 43020-1126 should be about $35.

 

Well, I feel like a real noob, maybe I am jaja. I pulled apart the MC to clean the piston and check the seals. I was real surprised to find that in fact is leaking, just couldn't see until the dust cap was removed. Also the piston and the MC show a lot of wear, like if they've been rubbing together. The fluid was full of shiny specks, my guess its from the piston and cylinder. I think I read somewhere that aluminum will cause the fluid to turn dark, is that so? So I guess this is the end to a 9 month mystery that shouldn't have been.









Well, I guess I'm looking for a new MC. This one is 11mm, should I be looking for an MC that is larger, smaller or same if I want improve braking but with modulation? I've read a lot of praises for the 07+ CRF 250R/450R MCs which I believe is also 11mm. The plus is that Honda parts are about half price or less of Kawasaki parts here in Mexico, and much easier to find.

 

Glad you found the culprit. That quick discoloration of your fluid was the main warning sign to me. I'm no help on picking an exact and ideal match to your existing system. The 11mm piston may not be the only determining factor. Piston stroke, leverage, and such can also come into play. At least you found it. I'd suggest a braided brake hose. I like 'em.

 

A larger bore will decrease lever travel but you will lose brake force vs. the same force to squeeze the lever. I swapped the 16mm m/c on my SV to a 19mm m/c off of the gixxers and you have to squeeze harder but the lever always stays out. I figured that might be a bit more important when scrubbing off 150mph to enter T10 at Road Atlanta.

 

Because of your advice and comments I was led to look at the MC again and find the problem, so thanks! I haven't fixed the problem but at least now I'm fairly certain of what it is.

I've read of the upgraded MC from a KDX or KX that some members have used, and that MC is 11mm also. The CRF250/450 also use a 11mm, as well as dual caliper pistons of the same size as our KLXs. So it's not just the piston bore as TNC mentioned. I will probably get one these.

The crf mc is 140usd new, the kx mc is 180usd, just for the mc, no lever, so it will come down to what I can find used locally in good condition. If not then I'll have to order from the USA.

 

I'm sorry for your troubles, but not if my brake fluid turns grey really fast I can assume some sort of aluminum contamination (or similar). Glad you found the issue!