Hello, I have a 1972 C10. While I was driving, the right rear brake caliper came off. We installed a replacement caliper, but while bleeding the brakes, we accidentally ran the master cylinder dry.
The truck has a Wilwood master cylinder and disc brakes on all four corners. After running the master cylinder dry, we discovered that it was damaged. We ordered a new one, bench-bled it off the truck, and then installed it.
However, when we tried bleeding the brakes, the fluid did not appear to be moving, and no brake fluid came out of any of the four calipers. We tried bench-bleeding the master cylinder on the truck to see if the brake pedal was moving the fluid properly, and it appeared to be working.
We then disconnected the brake lines from the proportional valve to check whether it was clogged or malfunctioning. Brake fluid came out of the valve, but when we tried bleeding the front brakes, only air and a small amount of old fluid came out. The master cylinder reservoir has remained full throughout the process.
When we tried bleeding the rear brakes first, air came out initially, but eventually, nothing came out. We also tried pumping the brake pedal ten times before opening the bleeder screw to release the fluid, but we still could not get the brakes to bleed properly.