[DeTomaso] Another brake question.

[MikeLDrew at aol.com]

In a message dated 7/11/09 14 11 11, pantdino at aol.com writes:


> I bought my car with two stock rear calipers on each side. My 
> understanding is that the proportioning valve was removed (and I believe the shuttle 
> valve also) and that was OK because of the 4 rear-caliper situation.
> 
>>>That's probably more or less true.   Having two rear calipers on each 
side was a popular modification for a relatively short time in the 80s.   
> 
> >I have been thinking I would like to remove the extra 2 rear calipers 
> because they create more drag on the rear discs and increase the pedal motion.
> 
>>>The additional drag isn't really a factor.   The total drag is a 
function of pad area, and two stock calipers have less pad area than a decent 
aftermarket caliper.   The pedal situation is a different story; you've increased 
the total piston area being acted upon by the master cylinder, and that 
will normally change the master cylinder requirements.   You don't say if you 
have the stock master, or an aftermarket replacement?   If you have an 
aftermarket unit, and the pedal travel is too long, you could go to a 
larger-diameter bore, with the understanding that pedal travel will decrease for a given 
amount of braking force, and pedal *effort* will go up.

It is possible to go too far here; my Mustang was very difficult to stop at 
one point, because I'd gone to a (Mustang vendor recommended) master that 
was too large.   It took enormous leg effort to achieve sufficient power to 
actuate the brakes in a meaningful manner.   Going down from a 1 1/4 inch to 
a 1-inch bore transformed the car; I found the perfect balance between pedal 
effort and pedal travel.
> 
> Just to be certain, I don't need to replace the proportioning valve if 
> I?remove the extra 2 rear calipers?
> 
>>>Rather than replacing the stock proportioning valve, I'd urge you to 
install an adjustable one, then fine-tune it empirically.  Leave it wide-open 
initially, take the car someplace safe and test the brakes hard; your fronts 
will lock prematurely.   Then progressively restrict pressure to the front 
brakes and test the result; eventually you'll go a bit too far and the rears 
will lock first.   That's dangerous.   Back off a bit until you find the 
happy balance point where the fronts lock up just a little bit before the 
rears, and you're there. :>)

Mike



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