The power disc brakes on my 37 Plymouth coupe have felt soft since I have owned it. I have a dropped tube axle with the 37-48 Ford round back spindles.

I bled the brakes a couple of times without much improvement. My master cylinder had a very slight leak so I replaced it with a new unit which was bench bled before installation. Helped somewhat but not enough to say that I am comfortable with the performance of the brakes.

Looking at a couple of different disc brake kits thinking that I am going to just go new with everything including rotors, calipers, bearings, hoses etc. Finding two variations out there.

1) Uses a Chevy style rotor with Mopar 4.5 inch bolt circle and a 2.8 inch single piston caliper. These are the same calipers I currently have.

2) Uses a Mopar rotor and a 2.375 inch single piston caliper.

My question is would going from a 2.8 inch piston to a 2.375 inch piston make much of a difference? I think it should make the pedal a bit firmer but will it effect the stopping power? The master cylinder is a 1 inch bore by the way.

One reason I am thinking of using the kit with the smaller piston is due to the stock Mopar rotor being more readily available compared to the Chevy rotor with the Mopar bolt circle. The other would be what I believe the smaller piston would take less fluid to move and would be a firmer pedal, but I do not want to do that at the expense of stopping power.

 

I'll throw my 2 cents in..
1- I think the master looks to be a little small @1" ?
2- I think having a look at the residual valves or installing the higher ones my help.
Just food for thought...
also check to see how much drag is on each wheel. could be the calipers are pulling of to far?

Keep us posted...