Thread: Power Brake Vacuum

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Ok, I have a 1938 Chevy 2 Door Sedan with a 700R4 trans and a 350 SB. Now, I don't know what the bore size is or any of that on the master cylinder. I bought a complete set up with Corvette style master cylinder and booster as one. I then replaced all the brakes lines and a new combination valve, new Camaro calipers on the front with new rotors and brake hoses. I replaced the rear wheel cylinders, brakes shoes and turned the drums on the Chevy 10 bolt rear. I moved the Master and booster from under the floor so it was easy to get to. So that's now on the firewall. The Brake pedal ratio seems to be OK. The only thing I didn't replace were the two residual valves one 10 lb and one 2 lb. The brakes were bled numerous times and with the same results. I have changed the master and booster three times thinking one was bad. That had now change in the pedal at all.I checked the vacuum for the booster and at idle in park it's 18 lbs. But, when I put it in drive it drops to 141/2 to 15 lbs. When I push the pedal it seems ok for a little distance and then it just seems to bottom out. Then it's like pushing against a brick wall. No one can figure it out. I have never had a problem like this one ever working with brakes. If you need more info PLEASE let me know. I am really stuck here! Thanks for your help.

Do you get full pedal travel when bleeding the brakes? Your description of the action wasn't clear on that point. If it doesn't go to the floor with a bleeder open, you have linkage problems.

Yes, I bled them the proper way. Yes, I used PVC hose and it's hooked up to the back of the carb. Is there a way to check that check valve? Will having the residual valves in affect the brakes if left there? Thanks!!

Yes, the brakes were adjusted correctly and I have a full drop on the pedal when the valve is opened.