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

Ken Green kenn_green at yahoo.com
Sat Mar 31 17:52:59 EDT 2012


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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