Bad brake booster applying brakes by itself?

[BulldawgMusclecars]

We recently installed a Right Stuff Detailing 4 wheel disc brake kit, with booster and MC, on a '67 Camaro and I have to say it is the absolute WORST kit I have ever dealt with...misdrilled rear caliper brackets, 2 defective master cylinders (they wouldn't even pull enough fluid to bench bleed them!), and now, an issue with the brake booster. The booster pushrod is adjusted correctly, and we installed the kit-supplied pushrod on the master cylinder end, but after driving the car a short distance (1/4 mile or so) the front brakes will lock up! Oddly enough, if the power booster is disconnected from vacuum it doesn't do it, even after several miles of driving. I'm leaning towards the issue being a defect in the diaphragm of the booster itself, allowing the pressure in each chamber to be unequal and essentially putting pressure on the back of the MC piston as its driven. Has anyone else ever had, or heard of, this issue? The engine is a mild (essentially stock) 327, so it pulls plenty of vacuum.

[CFster]

Why don't you get a replacement booster from the local parts store for half the money? It's all GM stuff anyway.

[BulldawgMusclecars]

Mainly because it's a chrome booster, which the customer wanted. Looks like I'll be making a trip to Summit to swap it out.