Year, Make, Model

2001 Kawasaki KX250. I believe other model years, 99-02, are affected as well. If your front brake sucks, then continue reading.

Service Manual

Here are links to service manuals:

KX125 KX250 OEM Service Manual 94-98

KX125 KX250 OEM Service Manual 99-08

Symptoms

The front brake lacks stopping power. You can hit the lever as hard as you want and still fly over berms because you can’t stop in time. If you want to know how bad they really are, go ride any Honda and compare the difference.

Diagnosis

Before I get into the fix, I did have leaky fork seals and the oil did get on the brake pads and rotor. So after replacing the fork seals & pads, I scuffed the front rotor and bled the system really good. These changes made a marginal improvement. It wasn’t until I started swapping master cylinders from other models/years that I noticed a difference.

How-To: Swap A Master

I covered a CRF master cylinder rebuild here.

The Physics Behind Hydraulics

I had to ask myself why the Honda brakes are so much better? I decided to buy an entire front brake system off a newer CRF and find out for myself.

Here is the formula to consider:

• Leverage – The lever pivot distance is the same on the KX and CRF master. No gain or loss here. I try to position the master further towards center of bike to gain more leverage with my fingers.
• Brake line – many say that installing a SS brake line will solve the issue. Well guess what, Honda runs the same style line as the KX. Is this really the answer? I think a SS will change the “feel” of the brake, which will reduce the modulation and make it act more like an on/off switch. Just look at the formula above, a brake line can’t increase force or pressure, it simply transmits it from point A to B.
• Rotor size – I did not compare rotor diameter sizes. A larger rotor will have more leverage and be able to stop quicker. I was not willing to pay for the big brake kits available.
• Brake pads – I bought cheap pads when I replaced them. The compound can make a difference and is something I need to experiment with at a later time. I’ve read numerous people like to run Honda pads due to the compound composition.
• Piston area – The caliper piston diameter is the same between the KX & CRF, therefore the area is the same. No gain or loss here.
• Master cylinder – this is the part that I swapped and made a HUGE difference! I did not take the KX and CRF master apart with fear of damaging the dust boot, however can conclude that the piston diameter must be smaller in order to increase line pressure. I haven’t proven it, but if you look at the formula above, it is the only change that I have made. If you reduce the area, line pressure goes up. The downside is that it will require more lever travel in order to push the same amount of fluid.

Fitment

Fitment is tight. The KX line attaches in front, while the CRF in back with a slight bend in the line. Also, the Honda routing is shorter and runs inside the fork tube instead of under the axle.

Future Improvements

I’m still not 100% satisfied with the stopping power. Here is a list of future things I will try.

• Brake pads – I will try running the OEM Honda pads and see if they bite better.
• Brake line – I am going to swap in a stock Honda (maybe SS) line and it’s routing. It’s shorter and runs inside the fork tube. I will have to buy 08’+ KXF fork guards that have the line clamp provision.

Comments

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