[DeTomaso] Any interest in dual (no booster) brake MCconversion?

Mon Apr 2 00:50:03 EDT 2012

Will,

Doing the conversion, it's easy to mount the balance bar and MCs a bit higher and get the same ratio (I think it's 6.5 to 1) as the Wilwood pedal assembly.  But I think the stock ratio is about 5.5, so it's only about a 20% difference.

Ken

From: Will Kooiman <will.kooiman at gmail.com>
To: 'Ken Green' <kenn_green at yahoo.com>; 'Guido deTomaso' <guido_detomaso at prodigy.net>; detomaso at realbig.com 
Sent: Sunday, April 1, 2012 5:20 PM
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake MCconversion?

Ken is right.

What everyone is missing, though, is power brakes do not have the same
leverage built into the pedal as manual brakes.

If you remove the booster and replace it with a manual master, your brakes
will likely require at lot more force to stop.

That's why I used a Wilwood pedal assembly instead of modifying the stock
medal box.  The Wilwood pedals are designed for manual brakes.  They stopped
my car very well.

I chose the smallest bore masters, and I was using stock Girling calipers
with Porterfield pads.  I plan on upgrading to Wilwood 6-piston calipers
(after much deliberation).

-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of Ken Green
Sent: Sunday, April 01, 2012 3:48 PM
To: Guido deTomaso; detomaso at realbig.com
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake
MCconversion?

I know I'm not always right, but I think I am on this.  

Maybe I am not understanding what you are proposng? I think that you are
saying that dual (side by side) 3/4 dia master cylinders will generate half
the brake line pressure of a tandem 3/4 dia MC with the safe pedal ratio and
same force on the pedal?  

I don't think that is correct because the side by side MCs will move the
same amount of fluid as the tandem MCs for a given pedal movement.  I think
that utimately, the ratio of pedal force to brake line pressure is
proportion to the ratio of pedal movement to fluid movement, so the line
pressure should be the same for side by side, or tandem MCs of the same
dia..

Ken
From: Guido deTomaso <guido_detomaso at prodigy.net>
To: "detomaso at realbig.com" <detomaso at realbig.com> 
Sent: Sunday, April 1, 2012 11:16 AM
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake MC
conversion?

"I think you're suggesting you get half the pressure for the same pedal
force 
and leverage?  I don't think that's correct."

Yes, it is.

"A tandem MC has two pistons, and even though they are sequential versus 
parallel, there is still twice the area of each piston. "

No, there's not.

Guess it's not as obvious as I thought.  But there's no law requiring you 
understand the underlying principles before building or modifying brakes. 
Many 
here recommend you concentrate braking power at the front of a 
rear-weight-biased vehicle, for example.

GD

________________________________
From: Ken Green <kenn_green at yahoo.com>
To: Guido deTomaso <guido_detomaso at prodigy.net>; "detomaso at realbig.com" 
<detomaso at realbig.com>
Sent: Sat, March 31, 2012 2:52:59 PM
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake MC
conversion?

I think you're suggesting you get half the pressure for the same pedal force
and 
leverage?  I don't think that's correct.  All of this is about leverage, a 
combination of mechanical (the pedal lever arm) and hydraulic (ratio of
piston 
areas).  A tandem MC has two pistons, and even though they are sequential
versus 
parallel, there is still twice the area of each piston.  My personal
experience 
is that with proper brakes, I never push the pedal much for the brakes to
come 
on, and once the brakes start to engage, more engagement is much more a
function 
of force that pedal travel.  AND, if there are any problems, I can just add 
residual valves.

The correlation between dual MCs and the booster is the ugly vs cool factor,
and 
more usable front trunk volume.  Plus, a booster is a band-aid that falls
off if 
you loose vacuum.  If you engine fails and you hit the brakes, there could
be 
problems.

Ultimately the test will be how well they work.  I have big calipers and 13
in 
rotors, so I think I will have enough braking.  Someone with a lot more 
experience than I have ran the numbers and said with 3/4 dia MCs, I should
be 
fine with no boost.  That also will depend on brake pads, so I see how well
it 
works.

Goran has been using a nearly identical system for a long time.  It's
described 
in PI 113 pp 14-15.

Ken

From: Guido deTomaso <guido_detomaso at prodigy.net>
To: "detomaso at realbig.com" <detomaso at realbig.com> 
Sent: Saturday, March 31, 2012 1:43 PM
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake MC
conversion?

Oracle of the obvious, but:

You're combining two unrelated ideas, eliminating the booster and going to 
parallel cylinders.

Each parallel cylinder will only create half the pressure an in-line
cylinder 
will produce for the same diameter.

Unless you can physically increase the swing of the brake pedal, you'll
likely 
be chasing your tail:  smaller MC(s) , greater leverage ratios and the pedal

hits the floor before you skid; bigger MC(s), lesser leverage ratios and you

can't skid since the effort is so high.

While we're in the neighborhood, for all the problems associated with the 
ubiquitous tandem master cylinder ( difficult to bleed, failure of half the 
system goes unnoticed, expensive, more difficult to rebuild ) ; you don't
see 
that much conversion back to a single master, pre-'67 arrangement.

GD

________________________________
From: Ken Green <kenn_green at yahoo.com>
To: "MikeLDrew at aol.com" <MikeLDrew at aol.com>; "detomaso at realbig.com" 
<detomaso at realbig.com>
Sent: Wed, March 28, 2012 9:11:09 PM
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake MC
conversion?

You can easily increase the mechanical advantage by mounting the balance bar
a 
bit higher in the pedal arm and mounting the MCs a bit higher.

Next question?

From: "MikeLDrew at aol.com" <MikeLDrew at aol.com>
To: kenn_green at yahoo.com; detomaso at realbig.com 
Sent: Wednesday, March 28, 2012 7:37 PM
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake MC
conversion?

In a message dated 3/28/12 19 18 38, kenn_green at yahoo.com writes:

I can email photos to anyone interested.  It really cleans up the front
trunk.  
Maybe not a good idea with stock calipers, but if you have big brakes, seem
like 

the way to go.

FWIW, Geoff Peters has been struggling to make his GT5 stop after he ditched
the 

brake booster to save weight (!?)

He's got six-piston Wilwoods on the front and four-piston in the rear.  He
has 
gone through numerous different sized master cylinders in an attempt to get
the 
car to stop properly, to no avail.  It still requires an enormous amount of 
pedal effort.  I drove the car from England to Modena and back, and it
wasn't 
nearly as pleasant as it might have been otherwise.

The fundamental problem is that the pedal doesn't have enough mechanical 
advantage.  Normally when cars are available either with, or without power 
brakes, they have a different brake pedal depending on the application; the
one 
without power has a much higher leverage ratio.

What is your reasoning behind getting rid of the power assist?

Mike
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