Does anyone know if it's alright to use an 11/16" bore size front master cylinder on a single disc brake caliper..I know the standard uses a 9/16", but I have a good deal on an 11/16".. I'm running a Performance Machine 4 piston caliper if that's any help.. Thanks

 

I ran one on my roadking for a little while. a very hard pull on the lever to stop.
Have since switched to the 9/16 for single disc.
My buddy likes his as it is.
There was a diff in banjo bolt sizes between the two.
TOMMY

 

Interesting thread, why would bore size make so much of a difference?

 

I don't know..that's why I'm asking..all the catalogs out there say 9/16" bore for a single disc and 11/16" for a dual..and from the previuos post, it looks as though it does make a difference.

 

As with any mechanical system, and with physics in general, EVERYTHING is a "trade off". You give up one thing, to gain another.
In this scenario, bigger piston(bore) will give you MORE volume, but LESS pressure(psi = pounds per square inch). The caliper piston size(square inches) did NOT change, so thusly, you are applying less psi to the calpier piston which likewise translates to less force at the pad/rotor.

Laymen's terms - gonna take ya longer to stop.
Bigger piston = More volume, Less pressure

IF you went the other way, smaller piston, you'd gain pressure, but you'd lose volume displaced, and MAY NOT, that is MAY NOT, have enough volume to apply brakes fully, without pumping them(to displace enough fluid).
I experienced 'this scenario' on Black Betty (78 FLH). Stock Harley rear 'banana' caliper, but the previous owner had put aftermarket fwd controls on it, with a 5/8 master cylinder. Stock is 3/4. Push the pedal all the way down til it stops, would produce less than 1/2 the stopping power, as the master cylinder would not displace enough fluid to apply brakes FULLY.

The determining factor is the caliper piston. And it is the manuf (PM, GMA, etc) who calculates what diameter master cylinder piston is required for THEIR caliper piston size.

Make sense ??? Good. Onward and Upward.

IF not, post back.


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Thanks 'Bro..You make alot of sense..that's what's I was looking for here..You've been a BIG help..

 

Yes but doesn't the fact that you have two setups with the 11/16 more than make up the difference over the 9/16 single setup? I realize in relation to the OP's question your answer explains the problem with swithching the sizes and setups. Just wanted to point out that when the apprpriate sized bopre is used with it's intended setup it works well, it is only when things are used with something unintended that the tradoff becomes an issue.

 

Although your reasoning seems sound, you achieve pressure by flow being restricted, I know this sounds contrary to real life applications, but it would seem that a larger master would give greater flow, and thru restriction would give greater pressure. Is it the difference in the banjo bolt obstructing the pressure from being applied to the slave?

 

My take on the bolt size is more for the folks who go from single to dual disc. The Motor Co must not want us to mix-n-match.
Too much brake pressure and easy to lock front wheel.
TOMMY