OK, I need a clearifacition on this. I bought a brake pedal "kit" that included the brake pedal assembly, the dual 7" brake booster, and the "corvete" style master with the brake line fittings on both sides of the master. Its suppose to work on disc/drum brakes. I also bought a "GM" style poroprting valve. This is installed on my 39 Plymouth and I have a disc brake conversion with Volari rotors and chevy truck calipers. The rear brakes are 9" drums from a Dakota. It has all new lines (3/16") and all new hoses, the calipers were rebuilt (napa) and there are new rear wheel cylinders. The master was bench blead before being installed and gave good fluid supply from both fittings.

Pretty much, these brakes suck. The pedal pushes real hard (motor has 17" vacume at idle) and the rear brakes do not work. With the rear axle off the ground, at idle in gear (auto trans) you can have to push with both feet to stop the rear wheels from turning! The car stops with front brakes only. The brake pedel is firm and is not bottoming out, if you open either a front or a rear bleeder screw the brake pedal goes lower. There is no air in the system, and I can see the rear wheel cylinders move when the drums are off (least the driver side).

The pedal bracket is mounted to the firewall with 4 bolts and extends to the bottom of the dash where it is also bolted. The brake arm is 15" long from the pivot to the center of the brake pad and there is a master cylinder arm that is 5" long from the pivot to the center bolt for the master. There is about 1/4" to a 1/2" of deflection in the firewall when you push the brake pedal (need to add some bracing).

Things I have done that have made no difference: put washers between the master and the brake booster thinking the master wasn't returning all the way. Just got a lower pedal. Adjusted the bolt between the booster and the brake pedal-both directions. Blead the brakes (many times). Checked vacume source and amount of vacume. Swapped the positions of the brake lines off the master. Adjusted rear brake shoes (many times). I'm pretty much at a loss here guys, short of throwing the whole mess out and starting over. Summer is coming and I'm not going to drive it this way another summer.

I've been told my brake booster is bad, when you step on the pedal and start the motor, the pedal does not move. That should not have an effect on the poor rear brakes. I'm wondering if the 9" drums and the corvete master are the problem or maybe the porporting valve is defective (its burried in a hole). I would like to get this right on one try, money is a little tight, I'll buy what ever I need....once more. I can live with out the power long as the brakes all work.
What ya think?
Gene