Need some help with brakes

[radioouman]

Normally, I can handle this stuff, but this one really has me baffled.

My Dad was driving the '93 Dakota and hit the brakes hard and one of the steel lines on the rear axle broke. Of course he had no brakes, but he drove it home anyway. That weekend, we replaced the bad line and installed a new wheel cylinder, we bled the rear brakes (both sides) and thought that we had it fixed. However, while we were bleeding the system, the pedal started going right to the floor with almost no effort, and we could never get it to pump up.

I thought that it was a bad master cylinder, so we replaced it. No luck. The pedal still goes right to the floor. The Haynes manual shows a procedure to re-center the ABS proportioning valve, but that procedure doesn't have any effect. I feel that something is wrong with the ABS unit and it is allowing any fluid pressure to be bled off by letting fluid go back into the reservoir.

Does that sound right? Unless someone knows how to fix this ABS unit, I guess I'm going to have to replace it.

 

[Vette73]

You may have also blown the master cyl if it went dry and damaged the seals.


But rebleed everything one more time, ALL 4 wheels. Start with the R-R, L-R, R-F, and then L-F.

 

[boomerang]

I think you've still got air in the system. Did you bleed the fronts? If you ran the reservoir dry, you've got air everywhere. Bleed every bleeder you can find. There may be some on the ABS unit too.

I'm not a Chrysler guy, so I can't tell you with any certainty, but some ABS systems require hooking up an electronic device to the ABS to bleed all the air out. It cycles all the mechanicals to allow the trapped air to escape.

Think about it, what are the chances the brake line failed at the exact same time the Master Cylinder failed and the ABS unit failed? You've still got air in the system.

 

[radioouman]

If I still have air in the system, the pedal would be squishy, but I would have braking action. Right now, my Dad can put the brake pedal on the floor and I can still rotate the front wheels by hand, easily.

My opinion is that the o-ring valve inside the proportioning valve is bad. This system doesn't seem to need any electronic device to bleed. Autozone.com has a bunch of info on it.

 

[jagec]

If there's enough air in the system, the pedal can still go right to the floor. However, it's more likely that you've got a bad seal somewhere.

 

[radioouman]

I have bled this thing over and over, so I doubt that it is air.
I can hear the fluid going back into the reservoir.

 

[alpineranger]

Two suggestions:
1 The abs system often needs a computer command to purge it if a lot of air gets into the unit - normal bleeding won't do.
2 Unlikely, but it could be the booster is bad.