85 monte carlo brake problem.
a few years back the rear brakes on my wife's 85 ss monte carlo started locking up. so i bought new brake drums, & new brake shoes & did a brake job on the rear of the car. it did help, but not much. the only time they lock up now is when the car has sit overnight , then when we go down the driveway the rear will lock up in the gravel. after you drive it, it's good for the rest of the day. what the hell? the brakes aren't real good on the car & haven't been for a few years. i replaced the brake booster, & the proportioning valve & neither did any good. i've adjusted the rear brakes normal & loose & neither helped. there are no leaks or anything like that getting the shoes wet. i can slam on the brakes & nothing will lock up. it seems like the front brakes are a little weak, & the rear apply early. could the master cylinder be bad some how be causing this? the only two things i've not changes is the master cylinder & the metal lines, & the rubber lines on the front & rear.