I have a problem stopping in this 71 vette. The brakes are firm but only slowly stop the car. You have to really push hard to get the car to slowly stop and then hold it hard to keep it stopped. The motor has a ¾ cam and lopes. I thought it might be a low vacuum so I re-routed the vacuum lines from the intake manifold to the canister for the head lights. This seems to help a little but didn’t correct the problem. I suspect it might be the power booster but with the engine noise when the car is running, one can not hear a leak. The booster is about five hundred dollars and I didn’t want to spend that if it could be the proportioning value or something else. You guys have any thought on this?
Its sounds to me that your Power Booster may be shot. You have a few choices here that you will need to make and it will cost you no where near (Five Hundred Dollars) as you suspect. You can pull your booster out of the car and send it out to be rebuilt if you care to keep the original booster in the car. You can go out and purchase a remanufactured Power Booster. Some places that sell them may want yours as a Core to cover your Core deposit. The other choice (which would be my choice) is to buy a brand new one.
By purchasing a new one you would still be able to retain the original one still worth some money to resell or to keep and sell with the car down the road as an original part to the car. Collectors some times are picky about numbers matching parts. Hope this solves your problem and cost factor. I have had plenty of experience with these older Vettes since I purchased my first one in 1971 a used 67' Vert. Have owned at least one every year since then. As of right now I own two older Corvettes a C-2 and C-3 and don't plan on ever selling them. Good luck with yours!