Going to get the 69 Plymouth Fury inspected this afternoon I had power drum brakes..had to slam on brakes but not extremely hard...still had brakes get to DMV power booster not working (not good) At least I think that is what's wrong....pull out of DMV and no booster driving in traffic for 15 to 20 miles home..what's wrong with this thing could it just be air in the lines from sitting..checked the vacuum when I got home and has plenty...

What are the brakes doing?Is the pedal rock hard or is there no pedal?You dont say whats wrong.Rocky

They are rock hard but will stop with a lot of effort

I'd be inclined to think booster but if it has sat for along time it could be a lining prob. Might split the M/C from the booster & pull it forward several inches & start it & hit the brakes & report how it feels

check in the engine compartment first.
see if there is a split in the vacuum line and you hear hissing anywhere.
then unplug the line and see if it changes anything.
engine running rougher or whatever?

check if you can pull a vacuum on the booster.

checked and replaced the hose..There was no hissing though..no change..bled the brakes yesterday lot of air in the back rear but no change..clean fluid was surprised...pulled the hose off of the booster while engine running no change..still hard pedal..Taken the left side wheels off today to replace the (left hand threaded studs)

with a vacuum leak that size, the engine should have ran worse.
make sure you are getting vacuum through that line, then do a vacuum test on teh booster.

Air makes a mushy pedal.Bad booster makes hard pedal.Check the valve in the booster.Just pull it off.If vacuum releases with engine off the booster is bad or the rods are not correct.The valves can get plugged also.Rocky

Well back at it again..I split the M/C and booster pedal still hard..checked the check valve and swapped it out with another still no change..I am beginning to think it is the booster..took it out for a ride and hard brakeing the whole time and front end shook like crazy while braking..No fun driving with all drum brakes..any help needed..I just got this thing inspected and all new interior..I cant stop now ..

oh yea one other thing I put my head under the dash while the car was running shut it off and heard some hissing while pushing on the brake...(bad booster)...I even replaced the foam gasket between the M/c and booster

I guess your talking about the booster lining? RapidRobert

Thanks for your help.. its just kinda odd that it went out on me so quick I had put on brakes kinda hard and then drove about 5 miles down the road and no power brakes..When I pulled the m/c and booster apart I vacuumed out the booster because it had a lot of dirt in it hoping that would do it but not..

Good luck & holler on how it turns out as I need more PB edumacation in case I ever convert to PB

Shade tree test of power brakes:

1. With engine off, pump brakes 5-10 times to expend any stored vacuum in the booster.

2. Place foot on brake pedal with very slight, constant pressure.

3. Start the engine.

A power booster that is working will have the brake pedal drop under your slight, constant foot pressure once there's vacuum. A dead booster will leave the pedal where it is.

Note that a dead booster and one not getting any vacuum due to other failures (cracked/plugged vacuum hose, bad check valve) will manifest the same. You need to eliminate the vacuum supply issues before condemning the booster.