Will a 71/72 booster work on a 70 drum brake trk?

[70chevytruck]

Need to replace my master cylinder and booster on my 70 gmc 3/4 ton.....drum. brakes.

Will a booster mastercylinder from 71-72 work.? Wanting to go front disc in the future but need booster now.....will it bolt up and work?

[Longhorn 70]

I am told the problem is the 71/72 is for front disc. The drum brake master should have a residule pressure valve in it. This basically keeps about 10 lbs of pressure on the wheel cylinders with pedal not depressed. the disc master doesn't have that.

[70chevytruck]

I know the discs require a different booster and master.....just didn't know if a booster /master for a disc truck would adversely affect drum brakes.

[Longhorn 70]

I am also told that the residule pressure helps keep wheel cylinders from collapsing and mantains the proper activating rod/piston distance.

The master cylinders I have seen for disc are also bigger diameter bore than drum only. They also have a small dimple in the main piston rather than the deep dimple for drum masters.

This indicates as long as you are using the drum master and booster as a set or the disc master / booster you'll be OK but not optimum. The disc setup may have problems with the front brakes not coming on fast enough due to lack of residule pressure.

Then there is the proportioning valve vs. distribution block issue.