[DeTomaso] Another brake question.

[pantdino at aol.com]

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?? 


the master is a replacement-- a GM part I believe with?a black steel adapter (I'm out of the country now and can't check)

So 4 rear calipers will have twice the drag of 4,no?? Or does it really give better braking, and I should leave it like it is?

-----Original Message-----
From: MikeLDrew at aol.com
To: Pantdino at aol.com; JDeRyke at aol.com; detomaso at realbig.com
Sent: Sat, Jul 11, 2009 3:52 pm
Subject: Re: [DeTomaso] Another brake question.



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.

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.


>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?


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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