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616 Posts
Discussion Starter #1
Hi All

I have a 66 GT Coupe, 289 A code, The brakes are causing me some problems which I can not trouble shoot.


Sad to say I drive the car less than 100 miles per year.

Front Disk and Rear drum brakes were rebuilt 8 years ago and I have put less than 500 miles on the car since the rebuild. The calipers are from stainless steel brakes and the rotors are from Virgina mustang as with the rear brakes and hardware. The proportioning valve was rebuilt about 5 years ago and I have not made any adjustments to the valve. Brake lines were replaced 10 years ago.

I use DOT 5 brake fluid and try to purge the fluid every 2 yrs or so. I just flushed it 3 weeks ago. When I bleed the brakes all four wheels have great flow as the fluid is released out the bleeder.


Sometimes, when I stop my front wheels lock up with just the lightest tap of the brakes. The brake peddle feels hard all the time. Sometimes when it does lock up its only the right side. (when it locks up the tires skid and squeal). The rear brakes appear to be working properly.

Any thoughts or recommendations. I have not inspected the actual calipers in a few years, but the rotors look as if their brand new.

So what can I do to narrow the problem down?

Thanks in advance


1,241 Posts
I dunno much, but possible your right caliper is sticking, maybe alittle rusty from just none use. Maybe jack the front end put SWMBO in the front and get her to pump your brakes and watch and listen to the caliper. Compare it's operation to the driver's side and see if there's a noticable difference. Might want to look at you flex lines and make sure their not cracked. Good luck.

3,134 Posts
If both fronts are locking up instead of just one, then I think you might need to adjust your proportioning valve. It sounds like too much power is going to the front.

9,887 Posts
I have two suggestions. Overly touchy ft brakes
in a simple system, such as the one on a '66 GT,
are usually the result of funky front pads.
There is a chance that you need more pressure
to the rear drums...... so don't ignore that
possibility. On your situation, my bet is on
the front pads. Where did you get those?
Usually I hear the opposite complaint- "my
car takes Schwarzenegger to stop it." That situation
is almost always front pad related.
The old asbestos D-11 pads for your car sometimes
were really grabby out of the box. After some
use, they would lose the "edginess." If this were
twenty years ago, I'd almost guarantee you that
was the cause. Even today there are some strange
friction formulas being marketed- I wonder what
IS on your car?

I like to adjust the 65-66 prop valve to put
as much pressure to the rear as you can tolerate.

Two pressure gauges, one temporarily screwed into
each caliper's bleeder port, also would get rid
of a lot of guess-work on your situation. I got
a cheap set through National Parts Depot a few
years ago for use when I'm at home.

Akebono Corporation
Brake Systems Engineering Center
Farmington Hills, MI

616 Posts
Discussion Starter #5
Good idea placing a pressure gage on the front.....what pressure should I be looking for?
If I should change the pads any recommendations as to a brand? When adjusting the proportioning valve anyone know which way I should turn the valve? Where can i get a pressure gage to hook up to the calipers?

Thanks again


9,887 Posts
You're going to see anywhere from 650 to maybe
1100 psi at the fronts, depending upon how much
"leg" you're using. You're not looking at how
much psi you can generate as much as what kind
of pressure differential you may see. You should
see NONE. Same pressure both sides. This verifies
that both hoses are indeed new and one hasn't gone
downhill internally. (Loss of ID will cause some
interesting braking as you can imagine, when the
pressure at the right caliper is 750 and the left
shows 950... you're heading toward the center
divider..... pretty much RIGHT NOW)

For the Brake Pressure Gauges check with SSBC or
check into NPD on their part number 951-1.
$47.95 in their current catalog.

Pads are a sad state of affairs. I've gotten
street car stuff from Stainless Steel Brakes
with some success. The local part stores are
a crap shoot. Mustang Unlimited has a pretty
good offering for the D-11 pad design used
on the 65/66 caliper.
The last set of NOS C5ZZ pads I used were
circa 1974 (judging from the Chicago Tribune
newspaper they were wrapped up in in the box).
Definitely asbestos and they did pull like a
big dog to one side until they were bedded-in.
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