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Re: Rear Brake Swap

To: "Gary McCormick" <>,
Subject: Re: Rear Brake Swap
From: "Mike Kerr" <>
Date: Tue, 30 Nov 1999 12:35:12 -0800
No :-)

Mike Kerr
Roadster Restoration
3730 Todrob LN.
Placerville CA. 95667
Ph.# 530-644-6777
Fax# 530-644-7252
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-----Original Message-----
From: Gary McCormick <>
To: Thomas Walter <>; Datsun Roadster List
Date: Wednesday, November 24, 1999 12:42 PM
Subject: Re: Rear Brake Swap

>So I am thinking that  the tandem master cylinder (like on my '70 2000)
provides a balance between the front and rear brake; that is, the two
circuits (or whatever) are sized to compensate for the difference in slave
(wheel) cylinder diameters and therefore displacement volume, front and rear
; allowing balanced braking  (per the design intent of the engineer who laid
out the braking system). Have I got that right?
>Gary McCormick
>San Jose, CA
>  -------------------------------------------------------------------------
>Thomas Walter wrote:
>> 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
>> If you want the FRONT BRAKES to lock up first, use a LARGER rear wheel
>> 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" <>
>> >
>> >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:
>> >> To:;
>> >> 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
>> >> cylinders with the same amount of pedal depression. Think about it!
>> >>
>> >> Bill Kenyon
>> >> SRL311 KA
>> >

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