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

Will Kooiman will.kooiman at gmail.com
Mon Apr 2 11:53:05 EDT 2012


I see what you mean now.  I was thinking both pistons would move at the same
rate, but it's pretty obvious that the rear would move twice as far -
assuming the same bore for both.

And, if the pushrod moves twice as far, the effort would be roughly half.

Of course, that means it's even more important to have pedals designed for
your master configuration.  Inline masters would need more pushrod travel
than tandem masters.  Conversely, tandem masters need more leverage.

-----Original Message-----
From: Thomas Tornblom [mailto:thomas at hax.se] 
Sent: Monday, April 02, 2012 9:06 AM
To: Will Kooiman
Cc: detomaso at realbig.com
Subject: Re: [DeTomaso] Any interest in dual (no booster) brake
MCconversion?

2012-04-02 15:31, Will Kooiman skrev:
> I didn't realize they weren't connected, but I don't believe it matters in
> this discussion.

It does indeed matter.

>
> The force required will be a function of the fluid displaced in the
masters,
> which is really just a function of the bore(s).  And if you have 2 ports
> with 2 pistons/o-rings, you displace twice as much fluid - whether they
are
> inline or tandem.

Not correct.

Run the howstuffworks video, and you'll see that the rear piston moves 
twice the distance, compared to the front, and all your pedal force is 
applied to that single piston. In a side by side arrangement, each 
piston takes half of the force, which makes it twice as heavy for the 
same diameter cylinders.

The rear piston displaces twice the amount of fluid compared to the 
front. It must displace the amount of fluid needed for the calipers in 
that circuit, as well as the amount of fluid needed to move the front 
piston, so that it can feed the calipers in that circuit.

For a side by side arrangement, the piston area needs to be half of the 
area for an inline cylinder to move an equal amount of fluid into each 
of the circuits

The pedal travel/effort in an inline master cylinder will in fact be 
equal to the travel/effort of a single circuit cylinder. It is the rear 
piston that does all the work. The front piston is just a safety device 
which does not change the pedal force/travel needed.

Cheers,
Thomas.


>
> -----Original Message-----
> From: Thomas Tornblom [mailto:thomas at hax.se]
> Sent: Monday, April 02, 2012 2:48 AM
> To: Will Kooiman
> Cc: detomaso at realbig.com
> Subject: Re: [DeTomaso] Any interest in dual (no booster) brake
> MCconversion?
>
> 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.ht
> m
> 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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>>
>>
>
>


-- 
Real life:   Thomas Törnblom             Email:	   thomas at hax.se
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