Brake Master Cylinder - rebuild or buy new?

Found ours leaking out of the front rod.

Is it worth it to rebuild, assuming I can find parts - 2008ish Merlin MR29.

If we replace it, are they fairly generic, or pretty specific to chassis manufacturer and/or caliper?

We’ve got 5 days to get this done…found it during shakedown runs today.

I don’t have experience with this particular brand but most every European manufacturer uses their own design and most are rebuildable with a kit of rubber-like seals and o-rings. The rebuild is usually straightforward. You will likely need a good pair of snap ring players and the ability to bleed the brakes. With only 5 days I doubt you are going to find what you need, order it, receive and rebuild in that time frame. Unless you are not able to build pressure when applying the brakes, it will likely work fine till you can source the parts.

If you have some pictures, someone might be able to help you with your specific needs too.

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Did it sit after it started leaking? If so, then pitch it, there’s no chance of the bore being good. If not, rebuild it.

As long as you’ve got the right effective diameter (cc of fluid moved per mm of brake rod travel) and the brake fitting matches, any master cylinder can be made to work. Righetti or Intrepid are usually the “generic” cylinders that people use and they’re pretty good.

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Thanks. Here’s a pic.


I think it had been leaking before we got it, from some grime I noted on initial cleaning. Changed fluid and bled, then ran the kart for the first time today. Driver reported soft brakes. Evening cleaning showed fluid where rod enters.

Are you thinking it’s shot because of moisture absorption and corrosion?

Frankly, due to limited time I think new would be faster. I hate not rebuilding stuff, but it may be shot anyway.

Thank you both.

My suggestion: take it apart. Inspect the bore to make sure there is no scoring. If it looks good, get a piston/seal kit and that will (most likely) fix the issue. If it doesn’t, then change the whole master, you’ll be off by just few dollars for the rebuild kit…always worth a try.

If driver says it’s mushy but there is no leak, most likely you have some air trapped somewhere. On old karts this could drive you nuts, so best option is always throw in a rebuild kit for the master and the caliper and redo both.

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Yeah, that sounds shot. Get another one. How much does crashing cost?

Not sure where you’re located, but Franklin is the US importer of Merlin chassis’s and parts. Call over and Jamie or Michelle might be able to overnight you the rebuild kit.


Thanks all.

It’s not really the cost, it’s the idea of tossing something that could still be used. But I don’t have enough time to rebuild it and find it still doesn’t work.

Reached out to both Franklin and my local shop for parts or a full MC.

Had Franklin send parts and had my kart shop hone and rebuild MC same day. Looks like it’s holding fine. Thanks guys.

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