4 piston front brake upgrade help.

[ovlovder]

So, I'll admit, brakes are not my strongest subject.

What I have is a pair of rc51 nissin 4 piston calipers, braided stainless lines, and a CBR600F2 Master cylinder.

I just filled the system with motul 5.1, there is no air in the system, the pads drag a bit, and if you really squeeze the lever you can bottom it out. But the brakes are applying plenty of pressure.

My guess is Im using the wrong size master cylinder.

Any insight?

[SMF]

could be a master cylinder issue... I'm surprised you can bottom out the lever... you sure you blead the hell out of them? after bleeding I've never had the level get anywhere close to bottoming out on any bike I've owned (even when using both hands to squeeze it... but I'm a bit obsessive about bleading brakes )

[Doc]

Good you can bleed my rear brake when you come up.

I would say Master too. I bet the RC51's is bigger.

[ovlovder]

It must be, I blead it again and no air. One hand, to the grip...

[Doc]

Got a leak?

[SMF]

weird. if you're got a spare master around I guess try that, but there are hawk guys at loudon pushing a lot more than the stock calipers with the stock master (just can't remember their specifics right now).

Doc, I'll bring my mighty vac up. we'll make your brakes _scary_

[Doc]

I cannot thank you enough... :cry: tears of joy

[ovlovder]

Going to get a new 5/8 master from Hord, he seems to think it should do the trick...

No leaks for sure...

[ovlovder]

Just spoke with my Dad, he thinks there may be air trapped at the banjos. Will try to crack banjos during a re-bleed.

[Hordpower]

F2 master with RC calipers (or any dual, 4-piston) won't cut it. The piston bore of the F2 MC is too small and it won't push enough fluid. You will need a 5/8" Nissin, or 18mm Brembo radial, something like that. The semi-technical explanation is, the F2 calipers only have 2 moving pistons each, total of 4. The RC has 4 pistons each, total of 8. So, roughly, you are having to move the lever twice as far to move the pistons the same amount. Result: Mush.

[ovlovder]

Yea, I kind of figured the 1/2" MC from an F2 was a bit small, especialy since a Hawk stock MC is the same size and is moving half the piston of the F2.

I think I may have been a combination of things though...