72 C10 brake problem, need help please

[nelson-ohio]

I bought this 72 truck about 6 weeks ago, want to keep it more like a daily driver. When I bought it, I noticed a problem with the brake system, it does not work very well, only slows down the truck to a stop.

So the first thing I did after I got the truck home was to drain and bleed the system completely. All the parts are in very good condition, booster/master/valve all look like new. After that was done, it didn't help with the brake at all.

I decided to take it to a local shop where several older gentlemen works on older cars. It maybe more like a hobby for them now, but I don't doubt they have the knowledge to do the work. I have had other things done there in the past, and I was happy with their work.

After 4 weeks, they replaced the following parts:
- Master cylinder from Right Stuff
- 11" booster from CPP, they said the existing one was too small
- Proportioning valve
- SS line for part of the system they feel needs replaced
- Cleaned the front caliper to make sure it's working
- Adjusted the 454 to get more vacuum, they say it's getting about 16" of vacuum now.

The total cost is about $700.

I picked up the truck yesterday, but it's only marginally better. They admit it's not where it should be, but they are stumped why it's not locking up the tires like it should. I think they give up on it, they don't know what to do next.

Does anyone have any ideas or suggestions? I can post pictures or more info to help with the diagnosis.

Thanks.