47-55.1 Electric hydraulic power brakes problem

[TX3100Guy]

Previously, I installed a power brake setup in my 1953 truck. The system consists of a frame mounted master cylinder, along with a small electric hydraulic pump and reservoir. In the case of power failure, the reservoir is supposed to hold pressure to allow multiple stops before reverting back to normal non-powered brakes. I haven't had any issues regarding brake failure, just the opposite.

Since installing the system, I've only had modest use of the truck due to sorting out other various issues that I've posted on this forum (engine rebuilds, oil leaking, over heating, etc.). I have sorted them out one by one (with help from many of you) and wanted to begin driving the truck more.

During the overheating stage, I noted in the back of my mind, that after the truck ran a while it was taking increasingly more RPM's to get the truck moving from a stop, but I was mentally busy chasing the overheating issue (largely a timing and mixture issue) and didn't pay much attention to this situation.

Yesterday, with what I though was all issues under control, I took the truck on a modest 20 mile circuit and barely made it home. About ten miles into the trip, I noted again the RPM's necessary to get moving from a traffic light and then realized that I was unable to get the truck moving fast enough to get into third gear. I limped home in second gear, accelerator to the floor at about 15-20 mph with the truck at about 1500 - 2000 RPM.

When I pulled into the shop, I pulled in just enough to close the door, shut the engine off, which was beginning to overheat given the driving circumstances. I then tried to push the truck a few feet further to align it with my lift and found all four wheels locked up. I even put a floor jack under the rear axle and could not turn the wheels at all (yes I was in neutral). The jack under the front axle yielded two wheels that would just barely turn with much effort. It appeared that despite no brake pedal being applied, the four wheels were locked up tight.

About 30 minutes later after the truck had cooled and apparently the hydraulic pump had released some of its pressure, the wheels turned freely. At first, my thought was that the pump was not stopping when it reached the pressure required to switch it off, but then I realized that with the pump on or off, its pressure line to the master cylinder was always high, the master cylinder must be allowing that pressure line to seep through the seals of the piston to engage the front and rear brake calipers.

I have an email into the company that supplied the system www.abspowerbrakes.com but have not heard back from them yet. Today, I removed the relay to the pump so that the truck only has manual brakes, since the pump will not operate without the relay. Attached is a photo of the system diagram, any thoughts or advice are always welcome.