[DeTomaso] Aftermarket Disc Brake System for a 1973 Pantera
Tomas Gunnarsson
guson at home.se
Sun May 14 11:53:50 EDT 2006
Dave,
Now I see how you think with regard to the different pressures. I'll try to describe it in animal terms! :-)
The doors in a tandem cylinder are not side by side, they are behind each other like in a corridor. The broom handle pushes on the first door and behind it is a 500 lbs gorilla. This gorilla stands on roller skates and has his back against a second door. Behind the second door is another 500 lbs gorilla with his back against a solid wall. Each gorilla represents a brake circuit. Now as you can see, if you push the handle the first gorilla will hold the door just as well as if he was against a wall as long as the second gorilla is fit and present. If the first gorilla leaves (i.e. brake circuit fails) the first door will slam open but it will soon hit the second door (they're real close) and the second gorilla will have to resist the same broom handle force. Alternatively if the second gorilla leaves, the second door will hit the wall and the first gorilla will see the broom handle force alone. The whole time the broom handle will produce the same force but with different movement if one of the gorillas are missing.
If we bring in a prop valve it's like having the gorilla tell his buddy the chimp standing beside him that "Hey, now this broom handle is pushing so-so hard. Push your door about half of what your maximum is." The gorilla holds up just as before but the brake caliper sees a smaller force from the chimp.
Does this help? :-D
Regarding your ratio I'm surprised that the valve doesn't allow you to adjust that much. A stock system is close to 2:1 f/r I think. I have about 1:2 f/r (i.e. lots of rear brakes!) on my car and I'm able to adjust until the fronts lock first. Without the valve it's Spin City!
Tomas
----- Original Message -----
From: "David Bell" <davidabell at worldnet.att.net>
To: "Tomas Gunnarsson" <guson at home.se>
Cc: "DetomasoList" <detomaso at realbig.com>
Sent: den 14 maj 2006 16:56
Subject: RE: [DeTomaso] Aftermarket Disc Brake System for a 1973 Pantera
Tomas,
The piston area ratio in my brake system is 1.5:1 (which in percentage terms
is 60/40) front to rear. The static weight distribution is about opposite
that - roughly 40/60. Dynamic weight distribution is much more difficult to
determine but I'd really like my front to rear brake bias to be more like
1.3:1 or possibly even lower. At any rate, the brake balance that I desire
requires significantly larger rear piston area or a tandem MC setup with a
larger rear piston (though a stepped MC like you mentioned would also be an
option). The closest I can get by upgrading with commonly available rear
calipers (Wilwoods with four 1.38" pistons) is 1:35:1.
As far as how proportioning valves work or don't work, I realize that
pressure feedback through the MC may not sound logical. I'm working from
experience with my proportioning valve setup where I encountered reduced
braking force overall as I stepped up the resistance in the front lines (and
yes the maximum resistance is quoted by Wilwood at 57%). My somewhat
off-the-cuff analogy goes something like this:
Imagine two doors positioned side-by-side in separte door frames. The doors
can be opened by broom handles connected to a common lever on the floor in
front of the two doors. The broom handles are the same length and are at
the same angle and location on the two doors (identical leverage on the
doors). So when the lever on the floor is moved, both doors open equal
amounts. Now image that a 500 lb gorilla is leaning against the back side
of only one of the doors. The same amount of pressure on the lever will now
move the door with the gorilla a smaller distance (if at all). Because the
two doors are opened by a common lever operating two broomsticks, the second
door will also open the same limited distance as the first door. The amount
the second door can open is limited by the amount the first door can open.
In a brake system, the fact that the levers opening the doors are hydraulic
rather than broomsticks just serves to ensure that the pressure is
completely equal throughout the primary side of the system. The 500 lb
gorilla (proportioning valve) is still in there blocking the first door,
limiting the distance that the second door (caliper pistons) can be moved.
Or so it seems. Maybe you can correct my contorted logic?
Dave Bell
-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of Tomas Gunnarsson
Sent: Friday, May 12, 2006 11:30 AM
To: davidabell at worldnet.att.net
Cc: DetomasoList
Subject: Re: [DeTomaso] Aftermarket Disc Brake System for a 1973 Pantera
Dave,
That is not how a proportioning valve works. The valve reduces its output
pressure and does not affect the input pressure produced by the master
cylinder. The front and rear pistons are not mechanically connected in a
normal tandem cylinder, they are hydraulically connected. Hence the output
pressure from the mc is always identical front/rear regardless of prop valve
setting. It is not possible to affect the pressure of the unregulated
circuit by adjusting the proportioning valve on the regulated circuit.
Have you calculated the piston area ratio f/r on your setup? The Wilwood
valve is not adjustable over a very large range, it's intended more or less
for fine tuning a reasonably balanced system. Sometimes I see it speced to
reduce pressure _to_ 57% and sometimes _by_ 57% but either way there are
limits to how much unmatching it can make up for.
Tomas
----- Original Message -----
From: "David Bell" <davidabell at worldnet.att.net>
To: "Thomas Tornblom" <Thomas.Tornblom at Hax.SE>;
<pantera3641 at azballistics.com>
Cc: "DetomasoList" <detomaso at realbig.com>
Sent: den 12 maj 2006 02:57
Subject: RE: [DeTomaso] Aftermarket Disc Brake System for a 1973 Pantera
FWIW, I installed a Wilwood proportioning valve on my brake system thinking
that I'd use it to correct for a piston area imbalance between the front and
rear calipers (I have 6-piston Wilwoods on front and smaller single piston
C-4 floating calipers on the rear). After spending a fair amount of time
installing the proportioning valve, I found that no amount of proporting
valve adjustment would allow the rear calipers to come into play in a
satisfactory manner. The real impact of adjusting the proportioning valve
to limit the line pressure to the front calipers was merely to dramatically
increase the pedal pressure required to slow or stop the car. I could
actually adjust the proportioning valve to the point that my leg was not
physically strong enough to lock the brakes (and my right leg is not weak).
Bottom line, my stopping distances increased significantly with the
functioning proporting valve because I could no longer threshold brake.
My hindsight reasoning for why the proportioning valve proved to be of
little use is related to the dual master cylinder that most of us use. A
dual master cylinder essentially has both the front and rear pistons
mechanically attached to each other on the same shaft. So, line pressure
restricted by a proportioning valve on the front end of the hydraulic system
is essentially passed along to the rear calipers as proportionally increased
pedal pressure via the mechanically connected front and rear mc pistons.
The entire system sees restricted pressure - not just the front. So
basically, I've convinced myself that proportioning valves don't work in a
dual master cylinder hydraulic system.
Eventually, I removed the proportioning valve completely and actually have
more powerful, predictable, and better balanced braking as a result - even
though my front-to-rear bias is still too heavy to the front. In my case,
what I really need is greater caliper piston area in the rear (different
calipers) - not a proportioning valve in the front.
YMMV.
Dave Bell
-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of Thomas Tornblom
Sent: Thursday, May 11, 2006 7:36 AM
To: pantera3641 at azballistics.com
Cc: DetomasoList
Subject: Re: [DeTomaso] Aftermarket Disc Brake System for a 1973 Pantera
pantera3641 at azballistics.com wrote:
> I have the stock booster, with a GM master attached via an adapter
> plate. I also have a Wilwood adjustable valve attached so that I can
> regulate front/rear braking>
Thanks Ron.
Is this a stepped master cylinder?
Any vendor selling this and the adapter, or what GM car is this from?
I'm about to install a Wilwood prop valve on the front circuit, but I
should perhaps replace the MC while I'm at it and get a better balance
to start with? I have calculated that I need about twice the pressure to
the reasr than to the front with my GT5 brakes. The front piston area is
almost exactly twice the size of the rear pistons.
I assume I'll have to delete the shuttle valve if I'm installing a
stepped MC as there will always be a pressure difference front/rear?
>
> Ron Scott
Cheers,
Thomas
>
>
>
>
>
> ----- Original Message -----
> *From:* Thomas Tornblom <mailto:Thomas.Tornblom at Hax.SE>
> *To:* B. Seib <mailto:oldwheel at mts.net>
> *Cc:* JDeRyke at aol.com <mailto:JDeRyke at aol.com> ; DetomasoList
> <mailto:detomaso at realbig.com>
> *Sent:* Thursday, May 11, 2006 5:07 AM
> *Subject:* Re: [DeTomaso] Aftermarket Disc Brake System for a 1973
> Pantera
>
> B. Seib wrote:
> > Hi Jack
> > No, it was this one.
> >
> > http://www.precisionproformance.com/bc2000.htm
> >
> > Best Regards
> > Barry
> >
>
> Anyone know of a stepped master cylinder that doesn't need a new
> booster? I would like to have about a 2:1 cylinder area front:back to
> get more out of the rears.
>
> Thomas
> _______________________________________________
>
> Detomaso Forum Managed by POCA
>
> Archive Search Engine Now Available at
http://www.realbig.com/detomaso/
>
> DeTomaso mailing list
> DeTomaso at realbig.com <mailto:DeTomaso at realbig.com>
> http://ftl.realbig.com/mailman/listinfo/detomaso
>
> !DSPAM:44632b8c261521369023592!
--
Real life: Thomas Törnblom Email: Thomas.Tornblom at HaxSE
Snail mail: Banvallsvägen 14 Phone: +46 18 290 290
S - 754 40 Uppsala, Sweden Cellular: +46 70 261 1372
Fax: +46 18 290 291
_______________________________________________
Detomaso Forum Managed by POCA
Archive Search Engine Now Available at http://www.realbig.com/detomaso/
DeTomaso mailing list
DeTomaso at realbig.com
http://ftl.realbig.com/mailman/listinfo/detomaso
_______________________________________________
Detomaso Forum Managed by POCA
Archive Search Engine Now Available at http://www.realbig.com/detomaso/
DeTomaso mailing list
DeTomaso at realbig.com
http://ftl.realbig.com/mailman/listinfo/detomaso
_______________________________________________
Detomaso Forum Managed by POCA
Archive Search Engine Now Available at http://www.realbig.com/detomaso/
DeTomaso mailing list
DeTomaso at realbig.com
http://ftl.realbig.com/mailman/listinfo/detomaso
More information about the DeTomaso
mailing list