Lou, I am glad to see that someone has done the legwork (hee hee) on
substituting a dual system master cylinder for the original. However, I
don't think a person should be diddling with the size of the rear wheel
cylinders, as even small changes will have an effect on brake balance. If,
over the years, the linings and front brakes remained constant, it is very
likely the changes to the rear slaves were an attempt to fight premature
rear wheel lockup under hard braking. If the rears lock up, you loose
directional control, unless you let off the binders and hit the object you
were in a panic to avoid. A very awkward situation which I am personally
familiar with. Another variable (besides lining and brake area) is the
amount of servo built into the drum brakes. This serves as a primative
power brake, and I believe was used mostly on American cars. I have no idea
how the Alpine brakes are designed.
On to the dual system. The early dually's (American Motors) used a "Dual
Diagonal" (left front plumbed to right rear, etc.) system. I have seen
others that are front/rear split. Does anyone know which is best and why?
Bill
----- Original Message -----
From: "Louis & Laila" <bwana@c2i2.com>
To: <ellis838@concentric.net>; <alpines@autox.team.net>
Sent: Thursday, February 15, 2001 1:09 PM
Subject: Re: Wilwood M/C
> Jim,
> Are you lucky or what?! I just spent the last week figuring this all
> out! I had my physics books, and automotive repair books all laid out. I
> even had help from the physics genius at UCSD! SO, here is the $64,000
> answer.
> Think in terms of a simple system. i.e., a master and a slave, with
an
> area of 1" square face on the piston. If 100 pounds of pressure is placed
on
> the master, that will transmit exactly 100 pounds of force through the
> slave. Now, increase the diameter of the slave cylinder to 2" squared, so
> that it is twice as big as the master. If 100 pounds is placed on the
> master, there will be 200 PSI through the slave.
> Now, rather than have 1 slave twice as big, just put two slaves, each
> with a face of 1 square inch. The pressure in the system is still the
same,
> no matter how many slaves there are. Therefore you will have two slave
> generating 100 pounds, for a total of 200 pounds. In a car, with 4 wheel
> cylinders, you would have 400 pounds of force for the one master at 100.
> Going back to the simple system, you can see that decreasing the size
> of the master or increasing the size of the slaves, creates the best
braking
> for the car. So, the ideal situation, is to have wheel cylinders that are
6"
> in diameter, and a brake master that is 1/4". OF course, that sounds
absurd
> because there is no way that the brake master could supply enough fluid to
> power 6" wheel cylinders. It would bottom out before the pistons moved
> enough to make contact with the drum.
> This is where the trade off comes. Here is a simple rule for you to
> remember. Smaller master equals MORE pedal travel, and LESS felt pedal
> pressure. Larger master means LESS pedal travel, but STRONGER quadriceps.
> You want to increase braking power, yet still have enough brake fluid so
> that your pedal doesn't bottom out. And, you would like to have a margin
of
> error, so that the pedal still could go down farther if there was a little
> air in the system.
> Lets talk about the early cars. They did not have a servo, so braking
> power was related to the quads of the driver. The series I & II used a
.700"
> master. It escapes me right now, but I believe they used a 7/8" (.875")
rear
> slave. The Series 3, which was boosted, used a .750", and the 4,5, and
> Tigers used a .875", and of course, they were boosted. However, on the
rear,
> they used a 3/4" (.750) slave wheel cylinder.
> So, you can see that on the early cars, to get the felt pedal
pressure
> down, they used bigger slaves in the rear, and a smaller master cylinder.
> On the later cars, since felt pedal pressure was reduced by the servo
> (when it wasn't sucking up the fluid or locking up), they used a bigger
> master for safety, with smaller slaves.
> All that aside, I drove my tiger without servo for 8 years every day
> with no problem. Now that I am servo spoiled, it would be a problem!
> There are 2 other things that affect brakes that you must think
about.
> The radius of the braking force at the wheel will affect how much pressure
> you need. If the wheels are ten feet in diameter, that is like a 5' prybar
> putting torque on the brakes. So, decreasing the size of the tires
DECREASES
> the amount of braking force required. And INCREASING the sizes of the
tires,
> requires trips to Gold's Gym and the quad master.
> The last one is the diameter of the brakes. A brake drum of 10'
> requires less force than the brake drum of 5', again, it is the prybar
> effect.
> The real "last" thing is pad composition, but that is a matter of
> choice and race conditions/requirements.
> So, all that said, you can't do much about your brake drum, or rotor
> size, so we look at them as constants. You will probably put smaller tires
> on, so this will reduce the amount of felt pedal force. You will also
reduce
> the master cylinder bore, so again, less pedal force. If you have a series
> 3,4,5 or tiger, you "can" get a set of rear slaves from a series I or II,
> and this will give you better braking force in the rear. You would have to
> experiment with this since you don't want these locking up on you before
the
> fronts take over.
> For safety purposes, I am going with a 13/16 bore, dual master. It is
> from a 82-84 Honda Accord. That way, if one system fails, I can still stop
> the car. To clear the Weber carbs, I moved the brake master to the clutch
> hole, and then welded in the gear for a clutch in the firewall, and used
> Tiger pedals and Tiger clutch master. I have strong quads! Lou
> ----- Original Message -----
> From: <ellis838@concentric.net>
> To: <alpines@autox.team.net>
> Sent: Thursday, February 15, 2001 6:13 AM
> Subject: Wilwood M/C
>
>
> > Hello,
> > Question, is the Wilwood master cylinder with the 3/4 inch bore big
> > enough to replace the stock 7/8 inch unit and not cause any braking
> > problems due to the different bore size. I want to use the Wilwood to
> > clear a set of side draft webers. Thanks Jim
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