1973 plymouth RR. car runs and drives great now but the brakes are very sensitive with little to no pressure on the pedal the front brakes will lock up would a booster that is going bad cause this? Car has sat for sometime before I started working on it for the original owner , nothing is leaking by the wheels ie calipers or wheel cylinders.

Have you tried adjusting the rear brakes to see if that helps the balance?

thanks for the reply, and to answer your question, no I have not.

What you describe is a symptom of a bad reaction valve in the Booster.

Have you made any changes/repairs to the brake system? were any changes made to the brake system when it was parked?, is/was this a prior problem?...just like to ask before the "ghost" chasing starts

car in question is a 73 Road Runner survivor car original owner 46K original miles nothing has been changed the car has been sitting awhile I am working on the car for the owner who has a buyer for the car and he wants everything in order for the new owner really nice thing to do anyway I have gone through the car mechanically tune up water pump radiator hoses fuel filter etc after a road test the brakes work but with the slightest of additional pressure you put on the brake pedal the fronts lock up first and hard I know I have to go through the brakes just so the current owner knows they are ok the master is sweating around the cap also there has been nothing done to the brakes and owner says they were working fine before the car was parked and every once in a while he would take it around the block not sure how often that was

Does it get better as it drives?

I had a bad brake line proportioning valve that kept hanging up. Made brakes very touchy early on a each drive, settled as it must have loosened up with maybe engine compartment heat. Anyway, changing it fixed it.

actually thought it did improve a little after backing up with the car and pumping the brakes as i backed up but after another regular drive it was acting the same If it is the proportioning valve is there any kind of rebuild for it or just remove and send cleaners through it along with compressed air

Offhand I would think it is a booster/check valve issue

I drove a friend of mines 69 RT Charger with power drum brakes and that was absolutely scarey the first time I hit the brakes it locked up all four tires and I barely touched the brake pedal, he was used to it and did't bother him but I was always curious to what the exact cause was since I had the exact same brake setup on my 69 Charger and they never acted anything like that.

I bought a new power brake booster for a truck a few years ago through mail order.

Same symptoms, just the slightest pressure on the pedal and BANG, everything in the truck headed for the windshield.

Took the booster to a local brake shop. He dropped small disc in the center hole, maybe it was a reaction disc, I don't know. Anyways the problem was resolved.

Regarding the valve. I never tried rebuilding them, just bought new and swapped out. There’s a couple of good sources...The Ram Man is helpful and will send you one that he tested first, In-line Tube sells them and I have had good experiences with them (but you have to know what you want in terms of the exact piece) and then there is Right Stuff Detailing (their website can be a little confusing in that products appear and disappear depending on which menu you use to enter an area). All three sell on e-bay, but I would research first. Or just call The Ram Man and talk to him, he can be a little crazy when it comes to brakes but he is a very good guy, knows a ton and has helped me a couple of times with various cars. Look up The Ram Man Inc online and it has his phone number.

Regarding the Ram Man. Ask to talk to Wayne directly. Tell him what it is doing and see what he says. As I mentioned above, I have worked with him several times, we discussed what I needed and that is exactly what I got. Good Luck

Pete what does the brake fluid in this car look like?? If it was sitting a good bleeding may be enough to get the moisture out and free up the proportion valve. Also try a replacement check valve on the front of the booster.
Ron

lining material can have a big effect on brake performance.

yup. I remember from my days of working at Sears auto center, that tehre was a TSB on Ford Rangers to that effect. Ford had come out with "updated" rear shoes for them for this reason.

and being a B body, I only ever remember driving 1 or 2 older (60s) B body, those having had 4 wheel drums.

but I have owned a couple 75-76 Cordobas, a 76 Charger SE and so have my parents... I still have a 78 Sport Fury. Every one of those had "touchy" brakes. every time I get the Fury out for the Spring I gotta "retrain" myself as to how to drive it...my parents late 70s B body wagons were the same. called "nature of the beasts". I think somewhere along the way (maybe a TSB there too?) about putting smaller dia wheel cylinders in the back end to cure that issue on that series of cars.

. the Dakotas that have replaced those cars that I have owned (currently have a 92 2wd and 96 4X4) could use just a little bit of that....

not real sure on the fluid car was sitting for a long time with the owner only driving very little the last few years the car is officially sold now the new owner has said that he is more than capable of doing whatever repairs are needed on the car, so the original owner has agreed to let the car go to the new owner with what ever items need attention. Wishing the new owner lots of luck with the car, it's a rare piece even though it's a 73 RR it does need tlc and after getting to know the new owner a little bit more it really sounds like the car is going to be in some really good hands now. Thanks to all who have replied.

OK cool, now are we allowed to see it???
Ron

I will leave that up to the new owner, he is a member of the board