[DeTomaso] tech question for anyone that has upgraded their brake system

[MikeLDrew at aol.com]

In a message dated 8/15/10 19 37 22, MikeLDrew at aol.com writes:


> The part in question is actually a pressure reduction cylinder,  
> which balances the front-to-rear braking balance on the stock system by
> reducing the PSI pressure to the front circuit.   This is done due to the
> mismatch between the front and rear calipers.   With your system, 
> presumably the
> front-to-rear   caliper sizes are appropriate for a mid-engined car.
> 

It's worth mentioning that I drove a Pantera in Canada last week whose 
previous owner removed this pressure reduction valve.   The result was that the 
front brakes locked way prematurely.   For all practical purposes, it meant 
that the car had NO rear brakes.   People who don't know any better are 
fooled into thinking that they have improved their braking by removing this 
valve (or gutting it) because the pedal is more sensitive, and it takes less leg 
pressure to achieve a normal stop, with this valve removed.   What they 
fail to consider is that the front brakes lock up long before the rear brakes 
start doing anything.   

In a panic stop, this car would have a much greater stopping distance than 
an unmodified car, assuming the driver used the correct technique of 
threshold braking (applying the brake to just prior to locking up the wheels, 
maintaining directional control).

None of this is relevant for a modified system like Boyd is discussing, but 
it's worth repeating for those who are still using stock brakes.   FWIW I 
drove another car equipped with functioning stock calipers at all four 
corners, Porterfield brakes, and retaining the pressure reduction valve in the 
front, and the brakes worked MUCH better.   Yes, it took higher pedal effort to 
achieve a stop from a given speed, in town.   But when you really lay on 
the brakes, the car actually STOPS instead of just prematurely locking the 
front wheels and then slithering into whatever it is you're trying to avoid 
hitting!

Also FWIW, I drove Peter Havlik's GT5, equipped with factory GT5 brakes 
(same as the Longchamp/Deauville/Gr3 Panteras used).   These are much bigger, 
better calipers and big vented rotors, and these brakes were terrific.   
While really leaning on them, I noted the rears wanted to lock up before the 
fronts, as the car started snaking side-to-side, a decidedly uncomfortable 
situation.   Later we tried a highly unscientific test on a dirt road to see 
which brakes locked first, and they were somewhat inconclusive, with the rears 
locking first sometimes, but not always.   The surface wasn't uniform enough 
to give an accurate test.

I advised doing further testing on the road, at speed, and if my experience 
was correct, then he really needs to plumb in an adjustable proportioning 
valve in the rear circuit, and step the pressure down a bit.

BTW, Peter's Pantera is *awesome*.   It benefits greatly from Pat Mical's 
suspension tuning, and coupled with his PIM 427 Windsor motor, it is by FAR 
the best-driving widebody Pantera I've ever driven.   If I owned a GT5 or 
GT5-S, I'd definitely be making at least some of the modifications Patrick 
offers, if not all of them.

Too bad PIM's engine builder failed to do his math correctly, and built the 
motor with super-high compression; it detonates badly even with 94 octane 
gas and demands constant use of octane additive, which is really BS.   I know 
Roland's PI< 427 needed to be torn apart and rebuilt immediately because of 
the same goof. :<(

Mike