Ford F150 - 1993 4x4 5.0 ABS Brake problem

ABS and Brake warning lights came on and rear whells started to drag and smoke. Replaced rear shoes, springs, wheel cylinders(one was leaking)and adjusters and bled the rears. Still had problem but not as often. Replaced the master cylinder and completely bled the whole system. The master had crud in the bottom and was leaking a bit from the bottom "screw". Brakes were fine and I thought the problem was solved. About two weeks later (this morning) the ABS and brake warning lights came on. Brakes felt fine but no ABS "pedal pulse" and it didn't feel like the brakes were dragging. Felt rear drums when I got to work and they were OK. Checked brake fluid level and it was ok. Any ideas? Could it be the rear ABS sensor? I think the truck has ABS on the rears only and that's why I haven't touched the fronts.
Thanks for the help!

wheel speed sensor maybe? or an ABS module. those are about the only components left that could cause the brake light to go off.

You are correct about ABS on the rears only. Ford installed a module under the truck called the Rear Anti-lock Brake System Valve. This valve is designed to provide anti lock to the rear brakes. Since the back end of the truck is lighter, rear brakes would be more likely to lock up when equal amounts of force are applied to the front and rear. This RABS valve is what reduces that force. It sounds like yours is failing. The would account for your brake indicator lights on the dash and that your rears had been locking up.

It's located on the driver side frame rail, on the inside of it, just behind the front driver side wheel well area. The image below should help.

Can that valve be repaired or cleaned?

As far as I know, once it has given up the ghost, that's it. The only place I was able to find one (without calling Ford directly) was on Rockauto.com. Do a search for p/n 122025. Unfortunately, it's not cheap, $141.79 after core refund. I'm sure that's not what you wanted to hear, but with your symptoms, and the fact you already replaced so much else, this has to be the culprit.

You should start by pulling the RABS codes. To learn how, click my black Bronco below and look thru the Brakes & Hubs album. There's a group of diagrams that deal with RABS near the bottom of the page.

I have a decent used RABS valve for sale. If you want it, read this post & then e-mail me.

How long can I go before repair? I just has to ask that question. Who has the $%^&# to answer this one? I know it's brakes but I've gotta to take a 350 mile trip to North Carolina next weekend and I don't know that I can find the part in time.
From reading the Haynes manual, if the ABS system fails, you still have the "regular" braking system. Is that pretty much true?
Steve and Vamp Killer and the other respondents to my posts, sincere thanks for the help. I'm still a bit green when it comes to working on my vehicles but with your help I'm startin to get a little brown around the edges.

If the ABS light is on and you're not hanging up in the rear, you should be alright, just no ABS....My dads '92 Explorer has had the light on for years, and we haven't had a problem with it yet.

Like Steve said, you really oughta pull the RABS codes before you go on your trip. It won't take any time to do, and if it turns out to be something really serious, you'll know not to go on the trip with the truck. However, if the RABS has failed, then ultimately, you have standard braking. If you are loaded down in the rear for your trip, you probably won't notice anything. Because the @$$ end of the trucks were light, that was why they put the RABS in to begin with. As with any repair that needs to be made, you can go as far as YOU want with it. How far the truck will go, or not go, is a totally different story.

I wouldn't attempt a trip with the brakes sticking. If it was JUST the ABS light, then: no problem. The brake system defaults to the old non-ABS system.

But yours has a serious problem that's affecting both systems.

Let me back up. After replacing the rear shoes, springs, adjusters, and wheel cylinders, I still had the brake "dragging" problem. After replacing the master 3 weeks ago, which was leaking and had rusty crud in the bottom, brakes work fine in both controlled and panic situations. The only symptom I have now is that the brake light and the ABS lights are both on constantly. This weekend, I am going to check the ABS diagnostics per your advice and do a visual inspection of the front and back brakes.
I found the ABS valve and noticed that there is a bleeder on it. I didn't touch this when bleeding the system. I bench bled the master, and bled the right rear, left rear, right front and left front in that order.
However, I am taking your advice and not takin the truck to NC. I'll probably take you up on the ABS valve. You'll here from me when I get back. Thanks again for the help.

Update: Visual inspection revealed low brake fluid in master. Checked all lines, pulled rears and checked wheel cylinders. Nothing bad there. Checked fronts. Found that front left bleeder was leaking. It looks like the old bleeder was cross threaded or the wrong bleeder was used. The threads were pretty beat up. Bought new bleeder and installed. I don't see any leaks. Both the dash lights are now out (ABS, BRAKE).

Door #1: Buy new front calipers?
Door #2: Tap new thread for offending bleeder?
Door #3: Do nothing. It's always an otpion.
Any suggestions?

Door #4:
Get a caliper from a junkyard.

Just an idea. If not, tap a new thread. Glad to hear your lights are out now.

Door #0.5: Get one new caliper - they're cheap, but there's nothing wrong with the other one.