Brakes locked up -- and fix found

[flainn]

I wanted to relate a weird experience I had last night...

My kid helped me flush the brake lines, then we went for a short drive down the street to make sure everything was working (I've been steadily making the brakes work better -- they were full of air when I got the truck).

I hit the brakes hard to get an idea of stopping distance. They felt normal at first, then I felt them grab *really* hard, harder than they ever had before.

When I released the pedal, the truck wouldn't go anywhere. The brakes locked up!

I was able to get the truck back to my house, by flooring it (it was either that, or leave it in the middle of the street). Bad, I know, but it was only a couple hundred feet.

Couldn't get the brakes to unlock in forward or reverse. So I did some Googling and saw that someone with a similar problem suggested pulling the ABS fuse.

That did the trick. I started the truck up without the fuse and the brakes unlocked.

Anybody have any idea what caused this? Do I need to get my ABS system looked at?

 

[flainn]

Also: I'm not having much luck bleeding/flushing the rear brake lines. Even with a helper pushing the pedal to the floor and holding it, I can't get much fluid to come out of the bleeder valves. Does that mean I've got air in the ABS controller?

 

[awood]

My experience with my 92 (RIP) was almost the same. Shortly after I got it, I bled the front brakes using a helper to push the pedal. When I moved to the rear brakes, no fluid came out - even with my helper pushing very hard on the pedal. Turns out that the RABS controller had rusted/corroded to the point that none of the valves would move, even after I took it apart and tried to free them.

My fix? I can't recommend this, but since I'd already taken it apart, I plugged the electronic part of the valve back in (to ensure the ABS light didn't illuminate) and bypassed the valve with a short piece of brake line.

edit: The 92 is the one shown as "wrecked" below, and no...it wasn't due to a brake failure

 

[Tony H]

I remember stumbling over a 'ABS bypass' on this forum. I'm sure if you do a search, you'll dig up some info.
I can't imagine it being anything else.

 

[92exp4x4]

I also have plumbed around the RABS valve on one of my '92s. The brake operation is no different without the valve, just leave it plugged into the harness and tie it to the frame or something. If you have to have it, Rockauto offers reman valves and there is a bleeder on it.

Oddly enough, that 92 was also totaled in a brake un-related accident, my speed was 0 at the time of impact. I'm seeing a pattern here...

 

[flainn]

Thanks, guys. I will add this mod to the list.

 

[ExplorerSport'93]

I'm hoping someone here can gimme a hand. I picked up my 1993 Explorer Sport about a couple of months ago, it had a ABS light on, i ran a computer on the pigtail on the drivers fender and it said i had a low sensor strength or something along those lines on my front drivers side wheel, so today i got around to replacing the sensor, I got it up to 15 MPH and hit my brakes, everything worked great! i just drove it around in circles and the light came on, i shut it off and turned it back on and the light went away, and so I'm assuming it comes back periodically... but after i restart the engine, its fine. I'll take any suggestions... thank you!

 

[OneofMany]

These abs systems are just plain not very good. these are the early abs systems not like the modern ones. If your front bleeds fine and the rears have no pressure: 1st of all you should have started on the RR, then LR, then RF, then LF. 2ndly you may have triggered the failsafe 'brake proportioning valve' they are usually located at the intersection of all the brake lines. Id have to look but in wondering if the abs has it incorporated into it. there should be a reset button on it. Sorry i have no specific knowledge off hand.

 

[OneofMany]

I'm hoping someone here can gimme a hand. I picked up my 1993 Explorer Sport about a couple of months ago, it had a ABS light on, i ran a computer on the pigtail on the drivers fender and it said i had a low sensor strength or something along those lines on my front drivers side wheel, so today i got around to replacing the sensor, I got it up to 15 MPH and hit my brakes, everything worked great! i just drove it around in circles and the light came on, i shut it off and turned it back on and the light went away, and so I'm assuming it comes back periodically... but after i restart the engine, its fine. I'll take any suggestions... thank you!

The computer has to relearn the normal values, driving in circles will teach it wrong ones. It will take normal driving and a number of ignition cycles.