Car is a 1971 Chevelle Malibu,350 eng.350 turbo trans..had power drum brakes..used all stock parts on a conversion to power disc brakes..parts used

Stock used parts
spindles/Prop Valve.Calibers/

new parts
brake pads/rotors/new lines/mc for disc brake cars

I also used the short rod from the master cyl to booster..kept the power booster that already there ..

mc was bench bled,and lines were bled..

I didnt change any of pedal holes..as someone once suggested because I didnt see any to change..

I have a hard pedal..and the rear brakes lock up easily..

could my booster be bad?

are you sure you have a proportioning valve, and not just a junction block? (Stock prop. valves in '71 are tubular in shape and made of cast iron, while a junction block is rectangular, and usually made of brass) In any case, I am referring to the type that mounts to the frame rail, not under the Master Cylinder. If u have one of those, it is either a different year setup (ie. 69, in which there is BOTH a prop. and junction block present)) or an aftermarket one.
Aftermarket prop. valves are rectangular as well, so that can be confusing if you aren't if your parts are factory) Anyway, lack of a proportioning valve would make your rears lock up immediately.
I know that the boosters are different for drum/ disc applications. maybe your problem lies there?

I went the same route as you. Bought all my parts from NAPA. Changed to a new booster, MC, caliper brackets (front and rear), threw out the prop valve, and bought a couple brass elbows, and stuff from a brake place locally, and put an adjustable prop valve in for the rear end. Bench bled the MC, then built a pressurized bleeding system out of a one gallon sprayer, and bled all four wheels, starting at passenger rear. Everything works great. I haven't had time to get a proper adjustment on the prop valve, b ut the car stops on a dime. (and leaves some change too) LOL.

From what I had read, some time ago, when this conversion is done, you can either get a disk/disk prop valve, or eliminate it, as I did, and put in an adjustable prop valve to adjust the rear bias. You might need to change the booster, since you have not. Not sure on that one. I just wanted all new stuff under the hood, and the cost of one from NAPA was reasonable.

You might want to read through some of the other threads on the brake conversion, just to make sure. I read, and read, and read some more, then read even more, before I bought any of my parts, and had a game plan going in, but that all changed when I decided to do the suspension "since I already had it apart". That's where it got spendy.

I did replace the dist.block with a used prop valve..should I just take a shot with replacing the booster?Napa brand ok to use?

No the booster will not make the rears come on sooner than they should,I'd be looking at the prop valve.

No the booster will not make the rears come on sooner than they should,I'd be looking at the prop valve.

would a bad prop valve cause the pedal to be hard?

would a bad prop valve cause the pedal to be hard?

Not that I'm aware of...That almost sounds like a MC issue. Are you sure your MC is for Disc front / drum rear application? (large reservoir in front, small in back), and that your pushrod is correct length? What is the bore size of your MC? (what vehicle did u buy it for?)

http://www.babcox.com/editorial/bf/bf50014.htm
Read the whole thing, but specifically "Diagnosing Metering Valves" near the bottom.

How much engine vacuum do you have? You need 14-17". I used a MC for a 78 corvette, but I have 4 wheel disc.