1991 Mark II (converted) Ford E-150 van with A/C, auto trans, and the smallest V8.

Though I seem to have a firm pedal without the engine running, usually when I start my van, the brakes are very weak and won't stop the van. After I apply the brakes several times while driving, the brakes get better and feel as though the pads are gripping the rotors.

I've replaced everything in the system at least once with standard parts from Advance Auto Parts and removed the antilock unit from the rear brakes' line.

I suspect the rotors or calipers or that the master cylinder is somehow now undersized. I've adjusted the rear drum brakes to a snug position, but the van still free wheels. I've bled the master cylinder as well as front and rear lines many times with the same bad results. The system doesn't appear to be losing any brake fluid.

I noticed that by design the rear flexible connector attaches to a hole in the rear axle, where apparently the brake fluid enters, for some reason I can't fathom. This makes me wonder if this could be the problem, because I have NOT replaced the rear axle.

Any advice or opinion will be appreciated.

Thanks.

Check for a vacuum leak to the power brake booster.

http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm

Thanks.

Unfortunately, I tried replacing the ABS unit, then I removed it entirely from the system with the same results. A bypass section of brake tube now sits where this unit sat.

Check for a vacuum leak to the power brake booster.

Thanks.

I can't find any obvious leak.

Any idea what the vacuum reading(s) should be? And where in the system to take them?