[DeTomaso] Aftermarket Disc Brake System for a 1973 Pantera
Tomas Gunnarsson
guson at home.se
Fri May 12 12:29:32 EDT 2006
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
More information about the DeTomaso
mailing list