First of all we don't know what year your truck is. That would be nice to know. Anyway here are some facts and questions.
1. A 1982 K10 uses a 1 1/8 bore MC. So that is what you want.
2. We don't know if your MC is on the firewall or under the truck. This makes a difference.
3. Your Proportioning valve may be faulty or the system needs residual valves....or a possible bleeding.
4. Your complaint/issue is hard to decipher. It stops at 45, but you don't know if it stops good enough to not rear end somebody? What does that really mean? Check the stopping distance and compare to a chart. Also "unable to lock the brakes"? Brakes should lock up and vehicle should skid. This is why ABS was invented. What makes you think brakes are not locking up? Surely the rears are, because you keep them adjusted? So if the fronts don't lock, it is a proportioning/residual issue. The proportioning valve is mostly for rear brakes. It's basic function is to make the rear shoes grab a little before the front, so you don't nose dive and....... the shoes have farther to travel and need a head start over the front pads. The front pads MUST BE KEPT very close to the rotor. That is what a 2lb residual valve in the front line is for. If the fluid tries to drain back to MC, It allows pads to get too far away. That is NO GOOD. A proportioning valve may not prevent this. That's why I asked where MC is mounted. Where is the proportioning valve mounted?
5. A residual valve keeps the pad from retracting too far. There are no return springs like on the shoes. So pads are supposed to just "relax" a tiny bit due to slight loss of pressure and probably the spinning rotor force.
Sharon, see what you think about all this.
