2005 E-150 van
Purchased new in 2005
Dealer serviced since new (small country dealer)
2000 miles per year on average
30,000 miles total
Van is garaged
New (not remanufact ured) master cylinder
New within past couple years rear brake master cylinders
Brake fluid level remains constant ....... no fluid leak
Brakes have been bled repeatedly by several mechanics
Van always stops just fine.
Van does not have cruise control but did come with an ABS ready master cylinder. New master cylinder matches the old and the cruise control line is plugged into it.

This problem started a year or two ago and I've been chasing a solution ever since. The van doesn't get used a lot and the problem doesn't seem to affect most braking situations.

The biggest issue is that when sitting at a stop sign or similar situation with my foot on the brake pedal it slowly drifts down until it is just about even with the gas pedal. When driving and stopping other than that the pedal feels fine although not quite as solid as it used to feel. Also if I'm driving down a steep hill that is say 50 yards or longer, and riding the brake pedal while going down, the pedal will again drift down.

The first thing done was to replace the master cylinder and then bleed the brakes several times over the next week or so when that didn't solve the problem. I fear there was nothing wrong with the old master cylinder and it was replaced needlessly.

Now the parking brake light is coming on intermittently when the driving brake pedal is pressed and released. I don't know if this is related to the drifting down brake pedal or not.

My thoughts on the problem:

1) Could be the rubber brake lines at the wheels are expanding just enough to let the pedal drift down? Don't know if this is possible with modern brake lines. These lines might be original to the van.

2) Is there a rear AVS valve (RABS) somewhere in the system? I read elsewhere on this forum that may need to be bled if it exists.

3) Could the brake vacuum booster be causing the problem. I also found a thread on the forum where someone said they have seen similar problems fixed by replacing the vacuum booster.

Any suggestions?

Thanks,
BH Davis