The Stovebolt Site Forums The Parking Lot Tons 'o Fun master cylinder problem

i need an opinion here, i'm converting my 59 3800 to power brakes, i got an after market kit that has a 1 1/8 inch master with 7 inch dual booster i was all ready to install it when i went to bench bleed it and pulled the cover, it has 1 large and 1 small fluid holding area that makes me think that it's for disc/drum not drum/drum well here's the deal i got everything plumbed with 10lbs pressure valves front and rear, the question is will it still work on the drum system, like that or do i need to plumb in a proportion valve? I went to the hot rod national's in louisville today and talked to a few big name makers of brake parts, some said it won't work others said go with it it don't matter as long as i got the pressure valves in the system, all of my hotrod buddys said run it and see if it stops, it shouldn't be a problem well i don't know if i don't run it i'm out 175.00 and have to start over again, and finding a 1 1/8in master was hard to do.

My opinion is it will work. There might be a checkvalve in the small resorvior side but it wont matter if you have residual check valves in both front & rear. You dont need a porportioning valve with drum/drum brakes. The valve in those just turns on the warning light in case of a system failure.

I talked to the guy that i got the conversion kit from and he told me that the size of the fluid holding areas doesn't matter, its the external valves that determine if it's a disc/drum or drum/drum master. I don't know what he talking about, i'm just wanting to know if this thing is gonna stop. can anybody elaborate on this topic?

You want about 10 lb. residual pressure on drum brakes. This is not enough to overcome the return spring pressure. It keeps the wheel cyl. cups seated so as not to draw air when the brakes are released. Disc brakes you want no more then 2 lbs. There are no return springs.

Yep that's what i did 10lb residual pressure valves front and rear

I used a '69-'76 Corvette master cylinder 1.125" bore. The master is for power brakes but also can be used for manual brakes because it has the deep hole for the brake lever push rod. I did not use residual valves and have a great pedal and excellent stopping ability. The master is on my '48 Chevy 3800 that has '54 3800 front and rear brakes. Installation was done 6 years ago. 18,000+ miles with no problems. The NAPA part number is M1974.