Help me improve my brakes

[RGAZ]

I agree, and the adjustable in the rear line is acceptable but this could cause the brake light to turn on if the difference is too great and plumbed before the dist block. Ideally you would plumb it after the dist block and switch or you can disconnect the light.

From my actual car, the braking was poor and yes the rear locked earlier until I changed the prop valve. He wanted improved brakes, this will get him improved brakes.

 

[slantsixdan]

The calipers with 2.75” pistons are a factory caliper and were used on everything but A-bodies.

The calipers with 2.75" bore are a factory caliper used on '76 A-bodies (and then a bunch of other applications, too: F-bodies, etc).

Any factory disk brake master cylinder should be fine for volume displacement.

Agree.

Further, I have personally run the 2.75" calipers with factory A-body master cylinders that originally had 2.6" calipers and with DoctorDiff's 15/16" master cylinder, volume displacement is not an issue.

Agree.

None of the systems - distribution block or factory proportioning/combination valve, reduce the pressure to the front brakes. So, the disks will get the same amount of pressure with either system, and that is determined by the master cylinder bore. So the disks will function the same.

Agree.

Now, the distribution blocks were for drum/drum cars, and they don't proportion. So the pressure sent to the rear drums may not be what you need with disks up front, because the only front/rear brake bias on the drum cars came from the wheel cylinder and drum size. The factory proportioning/combo valve reduces pressure to the rear drums.

…which is really important; see the rear-brakes link in post #16 of this thread.

 

[72bluNblu]

I agree, and the adjustable in the rear line is acceptable but this could cause the brake light to turn on if the difference is too great and plumbed before the dist block. Ideally you would plumb it after the dist block and switch or you can disconnect the light.

From my actual car, the braking was poor and yes the rear locked earlier until I changed the prop valve. He wanted improved brakes, this will get him improved brakes.

Yeah the only proper way to plumb an adjustable valve is after the distribution block, which is why I said it has to go in the rear line on the other side of the distribution block.

And I never said installing a factory prop valve wouldn’t work, I was just giving additional options that involve less plumbing.

There are also some folks here somewhere just running a distribution block with disk/drums. Personally I don’t think that’s a good idea, but depending on the cars suspension and tire set up I’m not gonna say it’s impossible to have a decent bias for a particular set up doing it that way.

The calipers with 2.75" bore are a factory caliper used on '76 A-bodies (and then a bunch of other applications, too: F-bodies, etc).

Dang it, I forgot about the ‘76 A’s! But yeah, standard on a lot of different Mopars from the era.

 

[RetroDude]

Very interesting following this thread as I have a similar problem as DodgeBoy. The car is a '70 Dart Swinger 340 with factory power front discs. When I got the car, it had NO brakes (pedal to the floor). I installed a new M/C. Now, the pedal is high and hard, but, the pedal pressure required is just nuts. I don't think lock up is even possible. The car brakes smoothly and evenly without issue except for the crazy pedal pressure. I don't think the booster is working, but, I don't think that's the issue. I have another '70 Dart that was a four wheel drum brake car that I converted to Wilwood front discs and used the same M/C that was in the car. That manual brake car stops fine from 120 mph without issue. That kinda makes me think it's not a M/C issue. I'm perplexed!

 

[RGAZ]

I don’t have much more to add. I added an adjustable prop valve in front of the dist block because I don’t use the brake light and got the rears setup nicely. My manual brakes are hard (duh manual) but they can stop the car quick when I stand on them if needed. Not like modern brakes but probably correct for 1973.

 

[Dana67Dart]

The car brakes smoothly and evenly without issue except for the crazy pedal pressure. I don't think the booster is working, but, I don't think that's the issue

If the booster is not working that is the problem.

Manual brakes take considerable leg pressure.

If the MC is smaller (or larger, I don't recall which right now ) than 1" the leg pressure is increased.

I'm assuming you have stock Kelsey Hays front disk and 10x1.75 rear drums.

Power brakes have a different ratio vs manual so without the vacume assist it is typically harder.

Diagnose your booster before tossing parts at it

 

[RetroDude]

If the booster is not working that is the problem.

Manual brakes take considerable leg pressure.

If the MC is smaller (or larger, I don't recall which right now ) than 1" the leg pressure is increased.

I'm assuming you have stock Kelsey Hays front disk and 10x1.75 rear drums.

Power brakes have a different ratio vs manual so without the vacume assist it is typically harder.

Diagnose your booster before tossing parts at it

Thanks for the tip. I've been undecided on what action to take for some time. I will follow your advice and address the booster issue and see what happens.

 

[Dana67Dart]

Easy to test.

Remove the vacume hose and cap it

If the brakes feel the same the booster is not helping.

 

[Bewy]

Good, simple, test^^^^