How to choose a new front brake master cylinder?

**Nick Fracture** · 9th February 2012, 12:54

Hi guys,

I lost the top off the front brake master cylinder on my '87 Honda Rebel 450. I've been trying to find a new one, but it's proving to be a little tricky.

I'm now thinking that since the bike isn't going to stay stock, I could just replace the master cylinder with a shiny new aftermarket chrome one.

My question is - what do I need to look for in a new master cylinder, to be sure it's compatible with my stock brakes & caliper? Is it the fluid capacity, size of the port..? something else? Obviously I'm pretty keen to get this right because I'm a big fan of being able to stop when I want.

Thanks in advance,
Nick

**bogan** · 9th February 2012, 12:59

Cylinder diameter, apparently there is a number cast into most masters which tells you what size it is, post up what you find on it.

Originally Posted by Nick Fracture

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Obviously I'm pretty keen to get this right because I'm a big fan of being able to stop when I want.

I'm addicted to brake fluid, but it's ok because I can stop whenever I want

**F5 Dave** · 9th February 2012, 16:25

depending on how much of a pendant your WOF man is they could claim that a MC change is requiring a brake validation & LVV certificate. A tleast that's what the VINZ chap told me.

They have a point. Some clutz could put a twin system cylinder on a single disc set up & decrease the leverage & hence power of the brakes considerably. Or one could buy some chinese pitbike crap & have the cylinder snap off when brakes are applied hard.

Generally if you keep the MC the same size you should be ok. Size cast on cylinder & should be something like 12mm or 1/2" for a single disc setup, or 5/8" for a dual.

**Nick Fracture** · 12th February 2012, 10:34

Thanks for the answers guys. 1/2" is what's stamped on it. So can I just replace that with any 1/2" cylinder?

**Drew** · 12th February 2012, 10:59

Originally Posted by Nick Fracture

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Thanks for the answers guys. 1/2" is what's stamped on it. So can I just replace that with any 1/2" cylinder?

Yip. That's all ya need.

**cs363** · 12th February 2012, 11:42

If buying from wreckers etc., it would pay to take the banjo bolt that attaches the line to the master cylinder with you to check the thread as they do differ between brand and models. Either that or get the original banjo bolt for the cylinder with it, assuming the size of the hole in the union on the hose is the same. That's about the only small issue you might strike.
Also, probably obvious but make sure you get the cylinder complete with lever to save hunting one down to fit. It's a good idea to note down somewhere what your new cylinder is off in case you need to buy spares at a later date such as levers or seal kits.