[DeTomaso] Brake problem

[Will Kooiman]

Thanks to everyone that responded.  I think SOBill hit the nail on the head.

The master, booster, and pedal assembly haven't changed since I bought the
car 5 years ago.  They look factory original.  It has worked perfectly
except for a very small brake fluid leak.  I've been nursing that since I
plan on replacing all of that stuff soon.

There has always been an inch or so of pedal travel (at my foot) before
there is any resistance.  I know that it's a common problem to have the rod
misadjusted, but since nothing has changed, I doubt that's it.  I drive my
car about 10,000 miles each year.  The brakes get plenty of regular
exercise.  If something was misadjusted, I would have noticed it when I
misadjusted it.

The only thing I changed recently was the jetting on the carburetor.  I've
been playing with a vacuum gauge and an A/F meter to dial in the carburetor.
BTW, I think my magic setting is 67/73 on jets and 1/4 turn open (I'm
running 1/2 right now) on the idle screws.  It is a Proform main body with
QFT bowls, metering blocks, and throttle body.  I have a 10.5 power valve,
but I think 12.5 or 14.5 is what I need.

All of the brake fluid was flushed 2 years ago.  None of the calipers have
been rebuilt.  I don't think it is a caliper, because all 4 brakes are
dragging.  One caliper wouldn't affect the other 3.

I plan on replacing the vacuum assisted brakes with a balance bar setup.  I
prefer manual brakes over vacuum.  I can get used to a pedal that is harder
to press.  I can't get used to the brakes suddenly getting hard to push when
the engine dies.

My dilemma is what to do next.  I probably should remove the booster and
clean it up.  I'd rather buy the balance bar brakes and install them.  I
might disconnect the vacuum line until the parts arrive.  Can you tell I'm
addicted to driving my car?

Will.


-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of SOBill at aol.com
Sent: Tuesday, May 08, 2007 9:24 PM
To: wkooiman at earthlink.net
Cc: detomaso at realbig.com
Subject: Re: [DeTomaso] Brake problem

Will,
 
When you hit the brakes, you open a valve in the booster which  applies 
atmospheric pressure to one side of the diaphragm. The Other side of the
diaphragm 
has engine vacuum and the pressure difference moves the brake  actuation rod

into the master cylinder. The pressure difference on the booster  diaphragm 
times the diaphragm area is added to the pressure of your foot to  apply 
pressure to the master cylinder.
 
When you are not using the brakes, there must be a small gap  between the 
pedal rod, the actuation valve, and the position where  the actuation valve 
opens. This gap is to allow for thermal expansion,  vibration, et al. If
your unit 
has never been apart and you haven't done  anything with you brake pedal,
and 
the brake pedal freely, fully retracts when  not in use, you could have a 
sticking actuation valve in the booster. A sticking  actuation valve in the 
booster will apply the brakes for  sure.
 
Booster innards are not rocket science. The booster be  disassembled,
cleaned 
and repaired. You, or any good auto brake shop guy with  gray hair can do
it. 
The internal parts are also quite standard.
 
Have fun,
 
SOBill  Taylor
sobill at aol.com



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