I have disk brakes front and rear on my 31 A build. Should I go with power brakes or manual? I'll be using one of the under the floor units. The manual would give me more room. I have had no luck in getting measurements from companys that sell the units. The car is channeled four inches and I'm afraid the power booster will show from outside of car. Manual would be fine, if it stops the car with ease.
I had a problem with the brakes in my late model the year before last. While I was talking to the brake man (and hot rod friend) at the GM dealership the conversation came around to power brakes (after we discussed how dumb it was to out a specific type of brakes on a hot rod). He said that he did not see the need for a power brake booster on anything that weighed less than 3000 lbs. So I have not answered your question but I have given you something to think about.
Keeping in mind that disc brakes don't offer more braking power than drum brakes do, they offer more, or better, control over braking power. You have to match the master cylinder to the system. A smaller piston diameter will decrease pedal effort, but increase pedal travel; and vice versa with a larger piston diameter. You may have to experiment with different master cylinders to get the right combination for your system. I would think that fitting a vacuum booster under a channeled A would be difficult. Here's some reading material on the subject: https://www.joesracing.com/master-cylinder-math/
I have 4 wheel disk brakes on my 62 Cutlass, front disk brakes on my 62 Studebaker wagon, front disk brakes on a Model A and when I used to order fleet back in the 70s, I always ordered manual disk brakes and I have never had a problem in any case. Warren
Actually weight is not the only key issue when setting up a proper braking system! You also have to consider the brake type being used, disc vs drum, both for the front and rear brakes used. also if using a single master cyl dia. and if it has two different bores. also if boosted or not One of the main issues is the fulcrum of the brake pedal arm length and its pivot point. The Wilwood brake people have an excellent site that has great info and easy to understand diagrams to use and help setup a custom to your car and brake system!! They are also great people to work with to help select correct sized components to give you a smooth balanced front to rear system! (never asked if I buying from them or not!) I built a Austin Healey 100-6 with a hot rod V8, big discs in front and original drums in rear. two master cyl sizes for each brake system. The system gave me one of the best systems I have ever used, be it a new hipo car a or a home built beater! Any other process you are just hoping and praying it's going to work for your car and not end up backwards into a tree the first hard hit of the brakes!! Been there done that!!
I owned a 1982 Chevy PU that was manual disc.Stopped fine.My 32 PU is manual disc up front,and it will put you through the windshield if your not careful.
I have manual disc/drum on the '31 and it stops fine. Don't use cheap brake pads and make sure your pedal ratio is correct.
Thanks for your help everyone! Do most use the under floor frame mount master and peddle units? Disc all the around should need a 1 inch bore?