[DeTomaso] Booster talk

Sat Jul 18 16:18:55 EDT 2009

The Pantera has an almost 50/50 front/rear weight split...

>>>Ah, no this is not correct Julian.  I believe it is closer to 43/57 (front/rear).
DeTomaso advertised it to be better than it actually was in real life. (Surprised? grin)

How many people have actually driven their Pantera down the road and tested whether they
can lock up their rear brakes?

>>>I know that I wore out a set of front Goodyear Fiorano F1s testing my braking system
after/during modifications.

I removed the stock proportioning valve, and replaced with an adjustable unit
(plumbed into the front circuit only), and made repeated tests (heavy braking at point of
lockup, several times) with each (slight) adjustment of the valve.

Like Jack DeRyke predicted, the optimal setting was almost neutral (no proportional valve
needed).  My brakes lock up in front first, and just before the rears lock up.
(As it should be.)
After switching from 17" wheels and modern fresh tires, now worn out by testing, and
driving... I went back to 15" with less-than-optimal tires... and for fun repeated the
brake testing.  The optimal setting was almost the same as with the other tires.

Bottom line I am happy that my brake system works so well, and with little or no need
for a proportioning valve.

My components are:
Stock calipers & rotors, Porterfield pads, Byars master - with 9" (larger than stock)
booster.  It has now been something like 5-7 years with this system.  Still good.

Chuck

In reality the braking efficiency depends on many fatcors like suspension, weight et.c and
particularly tire type. There is no one solution and to do it properly wheel strain gauges
or a four wheel rolling road are required (the latter being far more common in the UK for
MOT testing where they actually annually test your braking efficiency front to back and
side to side, plus the e-brake has to be able to stop the car on the rolling road!!)

Julian

> Date: Sat, 18 Jul 2009 20:16:40 +0200
> From: Thomas.Tornblom at hax.se
> To: MikeLDrew at aol.com
> CC: Thomas.Tornblom at hax.se; detomaso at realbig.com
> Subject: Re: [DeTomaso] Booster talk
> 
> Giving it a new try...
> ---
> 
> MikeLDrew at aol.com skrev:
> > In a message dated 7/17/09 23 33 47, Thomas.Tornblom at Hax.SE writes:
> >
> >
> >> It will still require a fair amount of pressure before it starts 
> reducing the pressure.
> >>
> >>>> What makes you say that? I was under the impression that a
> > proportioning valve does just that--convert X amount of inlet 
> pressure into Y amount of outlet pressure.
> 
> There is a knee after which it begins to reduce the pressure. Initially 
> the output pressure is the same as the input pressure.
> 
> See:
> http://www.tiltonracing.com/pdfs/98-1261_Prop_valves.pdf
> 
> >
> >
> >> It will have too much pressure on the fronts until that happens. I 
> want well balanced brakes throughout the entire range.
> >>
> >>>> Which is exactly what you should get. You wouldn't want a 
> non-linear
> > system where you got equal pressure until some threshold is reached 
> and then the pressure reduces from there. You'd want the reduction to 
> be constant.
> >> Come to think of it, having the prop valve in the front cirquit is a 
> stupid idea. During hard braking you get weight shift to the front, and 
> what you need then is to reduce the force on the now lighter loaded 
> rears to avoid having them lock up.
> >>>> The weight transfer is so instantaneous that you wouldn't gain 
> anything
> > by having increased pressure to the rears initially, then dropping 
> down to 'proper' balance. You'd want them to be proper all the time.
> 
> Yes, but the harder you brake, the more weight is transfered to the 
> fronts, so you would want proportionally more brake up front then, which 
> is what you'd get with a prop valve in the rear cirquit.
> 
> >
> >
> >> With the improperly balanced brakes of at least my car the fronts 
> will have locked up before you get to this point.
> >>>>> And you should be able to dial them in so that they lock up just 
> a bit
> > later than they do now (which is to say, the rear brakes would 
> contribute more to the total stopping cause).
> >
> > Mike
> 
> Thomas
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