This is getting pretty interesting.
Both Bill and Calvin are correct. Looks like they are saying opposite
things, but not really.
If you want the REAR BRAKES to lock up first, use a SMALLER rear wheel cylinder.
If you want the FRONT BRAKES to lock up first, use a LARGER rear wheel cylinder.
For you engineering students out there, still in school, have a little
fun with your MATLAB program. MATLAB provides a can routine to you can
see the static and dynamic results in the brake pressure.
The early (single) and later (tandem) brake master cylinders both have
a single pressure point on the pedal. For racing, it is best to use
an adjustable ballance bar and two seperate master cylinders (I think
Bill Kenyan has such a set up on his vehicle... been a while since I
have seen it -- or was that on Ralph's?).
QUICK CHECK: Step on the brake pedal... feel how far it goes to the
floor; Now pull up on the handbrake, and try again! If you feel a big
difference... you need to adjust the rear brakes. Obviously the pressure
was the same in both cases, yet the brakes would behave different under
braking... hint, displacement does play a big part of this.
Carrol Smith has a pretty good write up in one of his "... to Win" books.
Cheers,
Tom Walter
Austin, TX
P.S. For you engineering students: Front pistons are 2.125" diameter.
Master cylinder is 3/4". Rear wheel cylinders can be 11/16" , 3/4",
or 13/16". You'll always find the LARGER rear wheel cylinder will have
more STATIC pressure... but add displacement volume, and observe the
dynamic results.
>From: "Calvin Grandy" <cmgfam@sover.net>
>
>When considering fluid power (hydraulic brakes) The work is done by pressure
>not by distance. This is not the true definition of work i.e. Force X
>Distance, but is what we are considering. If the small cylinders move out
>more rapidly under pedal application, so what! The resistance to movement,
>when the shoes hit the drums, will result in a build up of pressure that will
>extend any sluggish members (front caliper pistons perhaps). When all the
>free play is taken up, then the real pressure will build, and the work of
>stopping can be done.
>
>If the wheel cylinders are smaller, the resulting braking force may be smaller
>(do not neglect the self energizing effect of the leading shoe) and there will
>be less pedal travel before the brakes start to "bite", A higher pedal action.
>Mechanical adjustment of the pedal linkage can reposition the pressure point
>of the pedal if desired.
>
>Please do not construe this as an endorsement for the exchange of wheel
>cylinders! I do not know what the results will be. I just want to make clear
>the nature of the system.
>Regards
>
>Calvin Grandy
>Vermont
>
>----------
>> From: SRL311KA@aol.com
>> To: toby@wolfenet.com; datsun-roadsters@autox.team.net
>> Subject: Re: Rear Brake Swap
>> Date: Tuesday, November 23, 1999 10:24 PM
>>
>> Hey list,
>> Pistons in smaller rear wheel cylinders will move further than larger
>> cylinders with the same amount of pedal depression. Think about it!
>>
>> Bill Kenyon
>> SRL311 KA
>
|