My ’84 200X I recently bought needed a replacement rear master cylinder since the original was in poor condition and a rebuild kit just wouldn’t do any good. After searching the forums I came across mention of the LTZ400/KFX400 swap. This seemed like a good way to go since these parts would be about 20 years newer and less expensive. I only found one thread with some detailed information for the 85/86 250R so I took a chance and bought a 2003 KFX400 rear master cylinder assembly that included both hoses and reservoir. Here’s my experience with going this route.
First step was to turn the threaded holes in the master cylinder body into clearance holes for the mounting bolts. Next I used 5/8” long spacers to locate the unit away from the frame due to the design of the LTZ/KFX master cylinder body which also required longer bolts. I also had to rotate the tube connector so it points up (the one that connects the master cylinder to the reservoir) to clear the frame. I reused the brake rod joint from the 200X since it’s shorter than the LTZ/KFZ joint and connected this to the arm in a slightly different way due to the offset (see pictures). I retained the 200X reservoir due to mounting issues with the LTZ/KFZ version, although you will need to heat up the hose to allow it to stretch onto the 200X reservoir connector.
If you go with a LTZ/KFZ master cylinder I suggest purchasing a unit with both hoses to avoid difficulties due to hoses being too short. I still need to address the brake pedal height, right now it sits too high, but this should not be difficult to remedy. Besides that I am satisfied with the outcome, newer parts and less expensive.
I imagine you could also use some kind of adapter plate for mounting, but this method will definitely work.
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