12.7mm master cylinder into 14mm equipped bike?

[Guest]

Hi there guys, I'm after a new reservoir for my front brake on my 1980 GS850G. They're all either destroyed and leaky like my current one or $60 new... which for a plastic tank is a bit rich in my opinion.

I'm currently looking at a new, complete master cylinder setup which is compatible with my system as it uses 10x1.25mm banjo fittings... but it has a piston diameter or 12.7mm and my original one is a 14mm unit.

Does this just mean that I will have to squeeze harder on my brakes for a given stopping force, or could it have other consequences?

- boingk

[tkent02]

Edit, what I have used is 14mm MC in place of the 5/8 inch ones. That worked fine on dual brakes. Have not tried a 12.7mm.

10x1.25, is that right? It's been a while but I thought we had 10x1.0mm threads??? Not sure but check it out.

[Nessism]

The 850 uses a 5/8" master (about 16mm).

[tkent02]

It's 1x1.0mm thread, isn't it Ed?

[Nessism]

It's 1x1.0mm thread, isn't it Ed?

Sorry Tom, never measured the thread size. The answer is in the archives, seen it mentioned here before on numerous occasions. I'm just too lazy to search it out.

[SVSooke]

That size MC is meant for single disc systems.You really need a bigger one for your 850's duals. Keep looking 16mm ones are out there at around the same price.Stock Suzuki threads for the MC are 10x1.00 at least on our bikes.Honda and others use 10x1.25 and so do newer Suzuki's .Oddly some European bike use 10x1.00,go figure.

[boingk]

Not a worry guys, that's exactly the kind of insight I was after. I'll keep looking for an appropriate option, and some braided lines while I'm at it!

Cheers - boingk

[Ghostgs1]

Wouldn't the reduction from almost 16mm to 12.7 be of concern? Unless my math is faulty the area of the piston surface would be about 64% of the original piston. The pressure required to brake the bike would have to be significantly increased would it not? The difference in thread class would be a moot point I would think, if you use the correct banjo bolt given that they are both 10mm diameter bolts. Ray

[tkent02]

Wouldn't the reduction from almost 16mm to 12.7 be of concern? Unless my math is faulty the area of the piston surface would be about 64% of the original piston. The pressure required to brake the bike would have to be significantly increased would it not? The difference in thread class would be a moot point I would think, if you use the correct banjo bolt given that they are both 10mm diameter bolts. Ray

You have the mechanical advantage backwards. Smaller diameter master means more pressure for a given finger pull pressure, or about 2/3 the finger pressure required for a given braking pressure. You will be moving less fluid, so you would need to pull the lever about 1/3 farther to move the pistons in the caliper far enough to apply the brakes..

Shouldn't be a problem with good brakes and steel lines, going from 5/8 to 14mm is no problem, maybe 12.7mm just a little too small.

Someone needs to try it and let us know. I will maybe.

[Ghostgs1]

You have the mechanical advantage backwards. Smaller diameter master means more pressure for a given finger pull pressure, or about 2/3 the finger pressure required for a given braking pressure. You will be moving less fluid, so you would need to pull the lever about 1/3 farther to move the pistons in the caliper far enough to apply the brakes..

Shouldn't be a problem with good brakes and steel lines, going from 5/8 to 14mm is no problem, maybe 12.7mm just a little too small.

Someone needs to try it and let us know. I will maybe.

Oh boy! You are correct of course. The older I get, the less I know. Ray

[GregT]

The Honda Hornet - I think the 900 - uses a 14mm M/C. Thread size on the output is 10 X 1.25 - and the integral mirror mounts fit the Suzuki mirrors too.

For years the std thread size on japanese M/C's was 10 X 1mm but more seem to be going to 10 X 1.25. Most calipers still seem to be 10 X 1mm though.