Front Master Cylinder Upgrade?

[justanother54321]

I have a 79 gs 850 with stock brakes. I my front master cylinder is leaky and the housing plastic is deteriorating. I would like to just replace the whole thing.

I was recently informed by a motorcycle race mechanic that I could get a lot more stopping power out of my brakes if I got a new master cylinder with a smaller piston than what's on my stock setup. So my question is, what are some bikes out there whose master cylinder will give me more stopping power and where can I get one?

As always and suggestions and comments are appreciated.

[Nessism]

Going with a smaller piston will give you more pressure for any given amount of hand effort, but the lever travel wil be greater which some people consider mushy. Guess you could offset that with teflon/stainless brake lines to some extent but clearly there is a trade off with going with a smaller master.

Regarding piston size, the dual disc bikes have a 5/8" piston and the single disc masters are typically 14mm. You can get a brand new aftermarket 14mm piston master on ebay so you might want to check on that.

[justanother54321]

Thanks Nessim,

Does anyone know of any specific bike makes and models that fit into the 13-14mm master cylinder piston size range? I'm looking to get something as cheap as possible.

[Nessism]

Thanks Nessim,

Does anyone know of any specific bike makes and models that fit into the 13-14mm master cylinder piston size range? I'm looking to get something as cheap as possible.

Single disc GS bikes use a 14mm piston.

[salty_monk]

Go for a modern sportsbike master cylinder.... Most have the piston size stamped into the casting.

You will ultimately get more power for given lever pressure with smaller piston but with more travel (make sure you don't run out of travel before you get good brakes...) 14mm piston has been used by a few & seems ok but in my opinion when I tried a couple of bikes it made no really noticeable difference to power, just made the lever "mushy".
Going this route to upgrade you also have no more resistance to fade than you have at the moment - that's to say you can get more pressure which will work but only until they get hot enough to fade away.
I use Twinpot Kawasaki calipers with the original or matching 5/8 piston. They work brilliantly in power & feel compared to the wooden feeling originals... Just my opinion again!

Dan