I have had vacuum-over-hydraulic brakes on every trailer I own for more years than I can remember.

I also have never had a system failure, NEVER.

I recently purchased another truck that came equipped with a vacuum brake kit.

The brand of this system is unknown and is somewhat different in outward appearances to some of the other ones I have.

The guys I got this truck from never in fifteen years used the vacuum-brake set-up, as they had no trailers that were hydraulic.

I WD-40ed everything for a couple weeks and freed things up somewhat.

Then, I hooked it up to a trailer that I knew worked perfectly.

The vacuum gauge climbed steadily to around 20hg.

I pulled away and got to coasting fairly decent, then applied the brakes and could feel no response at the trailer.

I did this three times with the same results.

Then, I pulled the manual over-ride cable; the trailer immediately locked down tight.

After pulling the hand-cable, now, if the vacuum lines are connected, and the engine is running, the trailer-brakes stay locked.

I physically released the cable-lever on the brake actuator, worked it back and forth a few times, and tried to get things to release; but, the brakes stay locked.

I tried un-hooking, and re-hooking, the vacuum hose couplings = brakes still locked.

I shut off the engine, waited several minutes, re-started = brakes still locked.

The trailer-brakes will remain locked, until I open the bleed-off valve at the tank; then, as the vacuum bleeds off, the brakes slowly release.

Close the bleed-off valve, fire up the engine, and she locks tight again.

Working the pedal in the truck has no effect.

What I need is a good pictorial break-down/exploded-diagram of these vacuum brake actuators.

I can find the kits for sale; but, nowhere I have looked offers parts, or help with trouble-shooting.

Can someone point me in the right direction for knowledgable information and a source for individual parts for these systems ??

I know of three brands of these systems, REDLINE, BLUDOT, and PASCO; I am sure there are others.

I understand that there is a diaphragm in the actuator.

Also, there are two vacuum-hoses that proceed from the actuator to the trailer, one is MANIFOLD, and the other is CONTROL.

One hose connects on the forward half of the actuator (the same end that the truck vacuum-pump connects to), and the other hose connects to the rearward end of the actuator.

Which connection is MANIFOLD; and, which connection is CONTROL ??

The actuator in question is the truck unit, not the big booster-control on the trailer.

Thanks for any help.