1997 Express 1500 soft brake pedal

Getting ready to dump my van. For 2000 miles I have been trying to address weak rear brakes and an increasingly soft pedal. Replaced calipers, pads, rotors, drums, cylinders shoes, proportioning valve, master cylinder and no improvement. Converted to rear disc brakes and no chnage. No, replaced master cylinder and vacuum booster, with no improvement. Brakes have been bled conventionally AND with a scan tool to activate the ABS pump. No help.

Any thoughts?

Getting ready to dump my van. For 2000 miles I have been trying to address weak rear brakes and an increasingly soft pedal. Replaced calipers, pads, rotors, drums, cylinders shoes, proportioning valve, master cylinder and no improvement. Converted to rear disc brakes and no chnage. No, replaced master cylinder and vacuum booster, with no improvement. Brakes have been bled conventionally AND with a scan tool to activate the ABS pump. No help.

Any thoughts?
What grade pads and brand are you using?
How far down does pedal go when stopping?

Does it stop good or slide wheels when pushed hard?

Engine off pump brakes a few times.
Do you then get a full solid brake pedal?
Any anti lock yellow or red brake lights on or anti lock brake codes?

Does it lose any brake fluid?

What grade pads and brand are you using?
How far down does pedal go when stopping?

Does it stop good or slide wheels when pushed hard?

Engine off pump brakes a few times.
Do you then get a full solid brake pedal?
Any anti lock yellow or red brake lights on or anti lock brake codes?

Does it lose any brake fluid?
1) Results are the same regardless of grade or manufacturer of pads.
2) With enough pedal pressure and travel (almost to the floor) the front ABS will function. The rears are almost useless.
3) Pedal travel is very long. No retardation until half way to floor. On jack stands, the caliper pistons are starting to move earlier in the pedal movement.
4) With engine off. the pedal gets hard when vacuum is depleted.
5) No lights.
6) Absolutely no leaks or fluid loss.

Based on some more searching, I am starting to suspect the BPMV.

You're probably onto something with the BPMV, The can leak internally and cause the soft pedal you have. Besides, I think it's the only thing you have'nt replaced, besides the rubber hoses.

You're probably onto something with the BPMV, The can leak internally and cause the soft pedal you have. Besides, I think it's the only thing you have'nt replaced, besides the rubber hoses.

And I have been under the car while someone mashed on the brake pedal. Another odd detail -- using a Phoenix injector, I can reverse bleed the FRONT brakes, but can NOT push fluid from the rears.

Just checked Mitchell On Line to read that the BPMV is under the EBCM and above the fender well. Guess I need to put my eye balls on that !!!! --- Just did. Saw a big control module under the master cylinder, but the brake lines route past it and under the body. Guess it's part of the ABS assembly on the left frame rail. YTBD !!!!!

So .......... it gets better (worse?). Replaced BPMV, no change !!! Pinched the rear circuit rubber hose and both front flex hoses. Pedal ROCK hard. Released the rear clamp, and pedal still VERY firm. Released the front clamps and pedal goes soft. Bled the fronts like crazy, no change. Oh, and I did have a scan tool to activate the ABS pump. NO leaks, NO (apparent) air anywhere, NO logical conclusions.

I am suspecting that the front calipers (replaced a couple years ago) may be incorrect (too large piston bores) and taking too much fluid volume.

Discussion.

So .......... it gets better (worse?). Replaced BPMV, no change !!! Pinched the rear circuit rubber hose and both front flex hoses. Pedal ROCK hard. Released the rear clamp, and pedal still VERY firm. Released the front clamps and pedal goes soft. Bled the fronts like crazy, no change. Oh, and I did have a scan tool to activate the ABS pump. NO leaks, NO (apparent) air anywhere, NO logical conclusions.

I am suspecting that the front calipers (replaced a couple years ago) may be incorrect (too large piston bores) and taking too much fluid volume.

Discussion.

Has the rear brakes shoes been adjusted up good with a good shoe fit on the drums?
Have rear drums been turned?

Has the rear brakes shoes been adjusted up good with a good shoe fit on the drums?
Have rear drums been turned?

When the rear circuit was blocked off, and the front circuit free to work, the pedal was long. With the front calipers pinched off and the rears open, the pedal was high. The rears have been converted to discs (there was no change in brake performance), but when they were drums the pedal was long as well. It is apparent that the front end is taking all of the master cylinder's capacity.

What I need to do now is crawl under a different early series Express and inspect the routing of the lines at the BPMV.

When the rear circuit was blocked off, and the front circuit free to work, the pedal was long. With the front calipers pinched off and the rears open, the pedal was high. The rears have been converted to discs (there was no change in brake performance), but when they were drums the pedal was long as well. It is apparent that the front end is taking all of the master cylinder's capacity.

What I need to do now is crawl under a different early series Express and inspect the routing of the lines at the BPMV.

In other words you may have things messed up converting to rear disk.
Good Luck

In other words you may have things messed up converting to rear disk.
Good Luck

The problem did NOT get worse with the disks!!!!! That is the amazing part. It is the front circuit that is causing the long pedal. As soon as I get some other stuff out of the way, I will dive back in.

The problem did NOT get worse with the disks!!!!! That is the amazing part. It is the front circuit that is causing the long pedal. As soon as I get some other stuff out of the way, I will dive back in.

And it did not get better or fix it right.
When you change over to 4 W disk you need to change master cylinder and abs unit and all valves and lines and sometimes the vacumn booster.

The problem did NOT get worse with the disks!!!!! That is the amazing part. It is the front circuit that is causing the long pedal. As soon as I get some other stuff out of the way, I will dive back in.

Does it stop good when you step on brakes at 60-70 MPH?

When you changed over to rear disk did you change master cylinder and other parts to match rear disk?

i would say get some clamps approved for brake hosem and clamp all hoses and see if you get a better pedal if not u know for sure its before the wheels. if its a good pedal release one clamp at a time til the pedal is crap again then u got it narrowed down