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

Mon Apr 2 03:47:41 EDT 2012

2012-04-02 08:40, Will Kooiman skrev:
> I agree that you get additional leverage by going with a smaller master
> cylinder.  The problem I had was finding a smaller master in the style I
> wanted.
>
> It wasn't a big deal with me.  I wanted to use the Wilwood pedal assembly
> anyway.
>
> I don't agree with what you said about an inline cylinder.  The rear piston
> doesn't push the front cylinder.  It is one long shaft with two sets of
> sealing rings (square o-rings?). The pedal is pushing both o-rings.

This is not how a standard inline dual master cylinder works, and I 
doubt that there are any cylinders like that.

Check:
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake1.htm
http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html
http://www.auto-repair-help.com/automotive_maintenance/master_cylinder.php

If both pistons were attached to the same rod, both curcuits would have 
to take exactly the same amount of flow to engage properly.

There may be a rod in between the front and aft pistons, but that is 
only a fail safe device, in case there is a leak in the rear circuit, 
the rod will act instead of hydraulic pressure to engage the front piston.

Thomas

>
> -----Original Message-----
> From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
> Behalf Of Thomas Tornblom
> Sent: Monday, April 02, 2012 12:42 AM
> To: detomaso at realbig.com
> Subject: Re: [DeTomaso] Any interest in dual (no booster) brake
> MCconversion?
>
> But wouldn't you just as easy get the additional leverage by going with
> a smaller master cylinder?
>
> I see that .75" dia cylinders are mentioned in this thread. I notice
> that Wilwood has .625" cylinders, which will provide 44% more pressure,
> or leverage, than the .75" cylinders.
>
> And inline cylinders will produce twice the pressure, at twice the pedal
> travel, compared to side by side cylinders of the same diameter.
>
> With a side by side arrangement, half of the pedal force goes to each of
> the cylinders, if the balance bar is centered.
>
> For an inline cylinder, all of the force is applied to the rear piston,
> and the hydraulic pressure in that circuit is then used to move the
> front piston, so the rear piston will travel twice as long as the front
> piston, and the hydraulic pressure will be the same in both circuits.
>
> Thomas
>
> 2012-04-02 06:50, Ken Green skrev:
>> 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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