Hello,
I'm having an issue with my brakes on my 97 B3500. I drove it, stopped for a couple hours, then started to drive it again.......as soon as I hit the brakes the pedal went much further down, but not entirely to the floor, and braking power seemed to be about 50%. My brake fluid was full to the top and no signs of leaks at the calipers, cylinders or anywhere else that I could see. I assumed I had an internal leak on the master causing me to only have front or rear brakes. I finished my 100 mi ride home with 50% brakes. I have now replaced the master, bench bleeding it first and then bleeding the 4 wheels starting with right rear. After all that the pedal still feels exactly the same...IE goes close to the floor and provides 50% braking. Am I missing something here? Stumped.
One other thing I forgot to mention, I now have the brake/abs light on which was not on before. My abs relays are missing and I assumed we're removed by previous owner so I've always assume my abs was non functional.. I've had the van for 4 years and have never seen the dash brake light on unless the parking brake was on. Any suggestions or ideas are appreciated!

 

You probably just have RWAL, so, no relays anyway. Did you get good fluid flow at all four corners?

 

I have an 02...98-02 are basically the same...a 97 is almost a 98 - I think...
I have had 5 real issues with the brake system. Hoses, rotors, ABS pump, shoes, and the pad mounting shims...
Out of those,,, the hoses or the ABS pump would be the closest to your issue I have had.

 

I believe I had equal flow from all four and I pulled enough fluid to see clear clean brake fluid at each wheel. Using a motivac hand pump i pull about 1.5" of fluid into its little container for each rear and about 1" for each front brakes. As I understand it, if the brake light is on, its either for the parking brake or it's detecting a pressure differential between the front and rear circuit. I'm not sure how you can get a pressure difference without a leak. The little metering valve that is part of the combination valve which you can observe operating per the shop manual appears to be doing what it should...extending slightly when the pedal is pushed. Could a failing hose cause a pressure differential? Yes this is a rear wheel abs van. So those relays aren't needed then? To Elkcon, I may be wrong but I don't believe there is any kind of abs pump for rear wheel only abs. I think it just uses 2 solenoids to cut the fluid flow to the rear if it detects wheel lockup.

 

On the end of the proportioning valve is what looks like a rubber button. If it seems popped out, press it back in.

 

Thanks Alloro, I think you are referring to that little stem that pops out under the rubber cover on the back side of the valve? If so that is popping in and out with the movement of the brake pedal. I believe that is how its supposed to work. Is that what you are taking about?

 

I found the source of my brake problem. I had a shoe spring give way a while back. Apparently when I replaced that I must not have gotten the bottom of one shoe seated correctly into the self adjuster. So, after going for 200 miles or so, the shoe slipped off of it leaving nothing between the bottom of the shoes. I think that caused the wheel cylinder to extend further than normal, making the pedal go further to the floor. I'm not sure what caused the brake and abs lights to illuminate however. Maybe the pressure dropped a little bit and that was enough. Thanks to you guys for your great thoughts on this.

 

Glad you figured it out...yea that funny brake feeling is from the rears...

My "valve" went bad and felt very similar to that...

I took a pic of the page out of my service manual if you needed it...glad you got it fixed

 

Yes, that's the one. It only moves when there is a pressure imbalance between the front and rear brake lines. The pressure imbalance is what causes it to move and trip the brake light, sometimes it will get stuck in the popped-out position, and you have to press it back in. The wire going to that proportioning valve is what triggers the brake light.