Below is a note I wrote last night to a guy who seemed to be having the same problenm I'm having...brake pedal goes soft when I start the engine. Please take a look and see if you have any ideas that might help.

Hello Nate,
I am having the same problem with an 86 240DL wagon. In a nutshell I have...
1. Completely cleaned the components from master cylinder to calipers so any leaks would be visible.
2. Replaced the front calipers and brake pads.
3. Bleed at least 3 gallons of Valvoline Synthetic (surpasses Dot 3 or 4 specs) through the lines. The first three times I used the buddy method. The last two times I used the pressure method with the system I ordered through IPD. The fluid is now coming out crystal clear as far as debris. I always make sure the clear line I'm using for bleeding runs upward for about a foot before going back down into a gallon bottle of flushed brake fluid. No air is returing into the calipers.
4. I have used a rubber mallet on everything but the proportioning valves (which I just found out about).
5. I have not found any external leaks.
6. I isolated the MC by plugging the two output holes and the pedal bacame rock hard.
7. With the engine on the pedal goes to the floor with only light pressure.
8. The air valve into the power booster is only allowing air to pass in one direction.

Tomorrow morning I'm starting again. Thought I'd follow the Bentley bleed method (LR, LF upper, RF upper, RR, RF lower two, LF lower two) using the pressure bleeder. While I'm doing this I'm going to beat the entire line/components from MC to caliper. What is the best sequence to use for bleeding? I've tried Haynes and Bentley without success to this point.

2/07/04
This morning I did the above blled sequence three times. The last bleed produced no air bubbles. I even raised the back approximately 1.5 feet higher than the front (read in the forum that it helped to raise the rear...really high. I kept the pressure bleeder at about 20 psi while I closed the nipples so no air (even though the brake fluid coming out was crstal clear) could return into the caliper.

At this point I am thinking that the rear proportioning valves (if that is what they are) which are located above the rear axle over the left half (driver side), have air trapped in them. They are the high point in the rear wheel brake layout. They are located at the top of the tunnel for the rear axle. It seems like the only flaw in a well thought out system. The brake lines (if I'm remembering correctly) pass through the middle of the cylinders instead of the top (which whould allow air to escape with bleeding). Last thing I did was to once again isolate the MC to ensure it was still good and it was rodk hard with the two output lines blocked.

Tomorrow I thought I would disconnect the two cylinders/propoertioning valves from the bottom of the car so that they can be lowered to a point below the rear calipers which I hope will allow any trapped air to escape...right?

Also, I'll replace the line running to the intake manifold from the power booster tomorrow as it is bulged at the spring clamp holding it to the intake manifold and looks like it's seen better days (even though it still proves to be air tight).

Any ideas from anybody out there? Could this be an ECU (electrical) issue that I'm missing?

My home phone is 864-297-8171 if typing isn't something you want to do. Believe me if I knew somebody to call I'd call. None of my friends can figure it out. My answering machine is always on as I'll be in the garage. This is turning into a real challenge. As John Wayne said...Life's tough....and it's tougher when your stupid.

Thanks for your input from anybody out there.