hello mopar friends
i have a 71 charger power brakes has a crate hemi motor been together for many years.always worked fine.

for the last year the brakes have been a stiff pedal. after driving a mile or so it would be fine like the booster was kicking in. sent it out to power brake booster exchange formally booster dewey.
thougth for sure the boot was bad. got it back and still have the problem. i know my vacuum is low around 10 pounds . tried a canister did not help.. anyone ever have this problem?
maybe a caliper ?
thanks for any help