1978 XS400 Rear Master Cylinder Replacement - any universal MC?


XS400 New Member
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Northern Virginia
Hi all -

I have a 1978 XS400 I'm working on restoring to probably flip. It's in beautiful shape, but the owner, for some reason that still baffles me, decided it was a good idea to drain the brake fluid when he stored it a few years ago. It basically renedered the entire brake system in need of a rebuild. I rebuilt the front master cylinder and put an XS650 front caliper on (the piston of the caliper on my bike had pitted to the point of being unusable).

This brings me to the rear master cylinder. It is so rusted and gummed up it won't come apart, and I actually broke the piston inside the master cylinder. I've done some reading on here and I see rebuild kits basically don't exist, and I'm not going to pay $100 for an original master cylinder on ebay that may or may not work. This leads me to finding some sort of universal master cylinder to use as a replacement.

Does anybody have any sort of universal master they've adapted to work for the rear of an XS400? I'm thinking of buying something like this:


Any input would be great. Thank you!
Brembo for the win but you need to fabricate a bracket to mount it to......almost the same as you have in the pic.

This is what I did on mine.
IDK if you could make it fit, but I probably have a setup from and xs850, which is a shaft drive bike, so it may not, but afaik, the calipers are same. I have a complete (nearly) 850 I will get pics of if you like, the cylinder is pretty small.


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I would be a good idea to replace that 40 year old hose with a new stainless braided style one. It will be far safer and work much better.