I just got a 74 corvette on the road, and I can't take the brake pedal feel. I have replaced all 4 calipers with remanufactured units, replaced the master cylinder with a stock remanufactured one, and checked all of the lines for leaks. I have bench bled the master and bled all 6 valves on the calipers twice. The pedal goes 1/2 way to the floor and I don't think it is caused by the lip seals becuase it is like this before driving the car.

It looks like the manual brakes have a 1" bore master, and the power brakes have a 1.125" bore master. If 200lbs brake pushrod pressure generates 2500psi ( .5^2 * 3.14 * 200 ) and the power boosted brakes generate 3500psi (.5625^2 * 3.14 * (200 + (4.5^2 * 3.14 * ( 14.7 / 2 )))) the 1.25" master bolted to the booster should provide 2850 psi.

Has anybody tried mounting a 1.25 bore master cylinder from a 1972 4wd k20 to stiffen up the pedal? Does this clear up the "410 psi reserve" issue with the duntov brakes?

I just got a 74 corvette on the road, and I can't take the brake pedal feel. I have replaced all 4 calipers with remanufactured units, replaced the master cylinder with a stock remanufactured one, and checked all of the lines for leaks. I have bench bled the master and bled all 6 valves on the calipers twice. The pedal goes 1/2 way to the floor and I don't think it is caused by the lip seals becuase it is like this before driving the car.

It looks like the manual brakes have a 1" bore master, and the power brakes have a 1.125" bore master. If 200lbs brake pushrod pressure generates 2500psi ( .5^2 * 3.14 * 200 ) and the power boosted brakes generate 3500psi (.5625^2 * 3.14 * (200 + (4.5^2 * 3.14 * ( 14.7 / 2 )))) the 1.25" master bolted to the booster should provide 2850 psi.

Has anybody tried mounting a 1.25 bore master cylinder from a 1972 4wd k20 to stiffen up the pedal? Does this clear up the "410 psi reserve" issue with the duntov brakes?
have you tried adjusting master cylinder push rod to get proper pedal travel?

I have adjusted the pushrod between the booster and the master cylinder with little luck. I have not taken the brake pedal to booster linkage apart, but I cannot lift the brake pedal with the linkage attached. I assumed that since there was no freeplay, there would be no advantage to adjusting the pedal in the car. Is this correct?

I have adjusted the pushrod between the booster and the master cylinder with little luck. I have not taken the brake pedal to booster linkage apart, but I cannot lift the brake pedal with the linkage attached. I assumed that since there was no freeplay, there would be no advantage to adjusting the pedal in the car. Is this correct?
not sure about that, supposed to be 1.8 inches of pedal travel from full release position with motor off. maybe you pedal or rod was bent in a wreck or something. does it stop the car quickly or is it like you have worn pads?

If you'll notice, your master cylinder sits in a very noticeable nose up attitude. Because of the nose up attitude, air gets trapped in the front end of the master cylinder's bore and won't EVER bleed out. To get the trapped air out, jack your car WAY up in the rear (or park your car on a steep hill) and then with the master cylinder's lid off, slowly pump your brake pedal. Little by little, the trapped air will bubble up out of the bore and go up into the reserviour. I discovered this little trick many years ago and have done it ever since. And I have SUPER good (and HARD) brakes on my '82 because of it. Try it..........

If you'll notice, your master cylinder sits in a very noticeable nose up attitude. Because of the nose up attitude, air gets trapped in the front end of the master cylinder's bore and won't EVER bleed out. To get the trapped air out, jack your car WAY up in the rear (or park your car on a steep hill) and then with the master cylinder's lid off, slowly pump your brake pedal. Little by little, the trapped air will bubble up out of the bore and go up into the reserviour. I discovered this little trick many years ago and have done it ever since. And I have SUPER good (and HARD) brakes on my '82 because of it. Try it..........
that sounds like a good idea ,he should try it before changing out more parts