Mid '70's pick up trucks generally used a 7/8 in. wheel cylinder instead of the more common 15/16 in. one found on cars. That's how I ordered mine.

the 15/16 disc master is the best( 1707) 4 bolt there is....super rare now due to wonderful expert advice and articles...no 2 bolt conversion,no master blocks..no adjustable brake rods..that are never long enough for good thread engagement..esp on e body
and it is era correct, AND LOOKS RIGHT

70 Cuda- I had 15/16 on rear. I found I had the 74 Dart 2.6" Piston Caplier on front.

I am swapping to the smaller MC now and ordered 2.75 Dippy Calipers.

Looking forward to the improvement.

Will swap pads when Calipers arrive. $23 for a loaded pair. Wholesaler closeout from ROCK. Wonder what pads are included?????

C-

You'll see a 12% increase in brake force by going with the 2.75 inch caliper. That might be enough to fix the issue right there. If not, swap to a smaller bore size
MC and test it again. Stepping up to the larger 11.75 inch rotors would also be a good way to increase front brake force.

(I covered a lot of this topic in my B-body book.)

Andy, thanks for insight.

Found the smaller MC at Advance last night and swapped in out. Loosened the rear shoes a bit while at it.

Went out and warmed up existing pads. Not much difference.

Tested prop valve and started to get bias with valve all the way out. I can notice the front begin to engage now as I get a bit of nose down went applying brakes at speed.

Once the brakes seemed as good as they'd get I did a few panic stops (15-20mph) and still get rear lock up.
Not as severe now, though.

Will wait for loaded Diplomat Calipers to arrive.

Any pad recommendation for those? May need to source a better pad.

I read up on Feets brake math.
I have calculated the Pedal Ratio to be 4.8.
The 65 Coronet has a 12" long pedal and the pushrod bolt hole 2.5" down from pivot.

With the existing setup 15/16 MC and 2.6 Calipers, I am only generating 695 lbs of line pressure.

So....If I redrill a hole at 1.5" I will increase the pressure to 1157.

Is this recommended?

This is a 65 Coronet and I just read that 65 and back B bodies have different pedals. There is also a hole lower than the one I'm using at 1 7/8" lower.
Does any one know if this is a Power or Manual Brake Pedal?

The car was converted to a 4 speed before I got it. I am thinking a Power brake pedal was used.

Thoughts?

Drilling the hole higher in the pedal will make the pedal feel softer with more travel.

Play around with master cylinder sizes and see if some odd size will work with your ratio.

Drilled the hole higher before I saw Feets' Post. Pedal sucks! DOH!

Found a prop valve in my stuff and will try to hold off rear brakes.

Will see how this goes...

Swapped the Pushrod back to stock location. The pedal came back firm.

Went for a first ride with the prop/combo valve installed. This si the prop valve for a 70 the has 2 parts. I only used the lower part that is similar to drum brake distribution block.

Took the car for a test and found the prop/combo valve makes a difference. Backs don't lock regardless of existing "adjustable prop valve" position.
Actually, the fronts work better with the adjustable letting more fluid to rear since it cuts them off quicker.

I would consider that braking is now good. I will move to 7/8 rear wheel cylinders and hope for continued improvement.

Do you think that 2.75 Diplomat Calipers will help the cause???

Thanks

I installed the 2.75 later Diplomat calipers. The Hose Mount location comes in from the bottom. This seems better than the A Body 2.6's that feed from top.

We installed the calipers and new Ambulance Pads (Metallic). The car seems to brake fine, but won't put you through the windshield.
Coming down driveway I was able to lock up both front first.


All in all its safe now. I will still try some adjustment and the 7/8 rear wheel cylinders.