The other day the Brake and Anti -Lock lights came on.
I bled the brake system and adjusted the rear brakes.
When I looked at the combination valve behind the master cylinder in the frame rail it had the metering valve tool C-4121 connected to the valve stem as shown in the service manual for the last 10 years that I have owned the truck.
What does the spring tool installed do to the brakes?(first question)
Checked the vacuum pump pressure which was 20 inches at both idle
and about 1500 rpm.
Disconnected the electronic control module behind the glove box.
The anti-lock light went out but the brake light was still on.
Checked the parking brake switch which looked good.
Had a spare used vacuum switch, so I connected it with no change to the brake light with the engine running.
What else do I check??(second question)

 

Check and make sure that your front calipers are not seized up or leaking. If they still have any, I picked up a set of rebuilt front calipers from Rock auto for 70 bucks for the pair, no core. It solved my phantom brake and antilock lights coming on after all other components were replaced. That tool holds the proportioning valve open in order to power bleed the brakes, I believe that it functionally disables the valve...Mark

 

Having that tool there will make the rear brakes suck. That valve keeps the front brakes from applying until pressure in the rear brake circuit goes up (from the shoes pushing against the drums). With that tool there, the front brakes are doing most of the work.

Stuff that turns on the red "brake" light:
parking brake switch
vacuum sensor
pressure differential switch
RWAL codes (any time the amber light is on, the red will be on)

Since the red light gets keyed 12v power, you can figure out where the trouble lies simply by unplugging stuff. When the light goes out, you have found what is grounding the bulb and completing the circuit.

The pressure differential switch should reset after a normal brake application - but sometimes they are sticky.

 

So do you disable that tool Dave?

 

What is the Pressure Differential Switch?

 

I am not sure what a pressure differential switch is, but here is a good description of this system; http://www.aa1car.com/library/abs_kelseyhayes_rwal.htm . I fought with my brakes for 2 years and I finally checked the front calipers, with no real indication of trouble, and found 1 piston locked in it's bore. Every component of this system must be working properly. Mark

 

I found the problem, but how do I fix it?
I had disconnected the Control Module, Parking brake, Vacuum Switch,
and last the connection on the Combination Valve just after the Master Cylinder on the frame rail.The lights stayed off. Next I reconnected everything except the connection to the Combination Valve.
The Brake Light and Anti-Lock Light now turn off after a second as they should.

What could be the problem with the Combination Valve?
Do I have air in the valve that is causing the unbalance between the two sides of of the switch?
Or do I need a new Combination Valve?

 

Try tapping on it with a hammer first. There's a spool valve in there that shifts when front and rear pressure is too far out of balance - as in you blew a brake line. After 15 years they don't always want to move back.

Air could be the problem. How is the pedal?

You have to buy the whole assembly.

 

I went over to my son's house today and got him to pump the brakes so I could bleed the system. First I hammered on the Combination Valve. Next bled the Anti-lock valve and the right rear, the left rear let out some air.
My son said the brakes were great after that.
Next we bled the right front and last the left front.
Went back and hammered the Combination Valve again, but the brake and
anti-lock lights were still on.
Also after putting the front tires back on I noticed more drag on both front
brakes when spinning the tires then they should have.
After we finished I drove 30 miles home on the freeway not having to use my brakes until I got off and then only eight or nine times.
When I stopped, checked the heat of the hub caps,the front were warmer
then the rear. but not real hot.

Does the Combination Valve put a pressure preload on the front brakes?
Which way does the spool move in the C.V.?
If I had a brake hose problem, I don't think it would be two at the same time?
Do I need a new Combination Valve?

 

Disc brakes always drag a little after applying the brakes in the driveway. Out on the road the little bit of runout in the rotors helps knock the pads out of the way. It sounds like the hydraulic system is OK.

The RWAL box is what is turning on the red light, check your ABS codes (how to in the sticky) and that will determine what you do next.

 

Well time to bring up an old post, I have just run into this problem (just this morning) and it got me a little bit worried. I do need to replace my brake booster due to it leaking air when I step on the pedal, could this be a possible culprit? Also when both lights come on they flicker for a few seconds and then go out then come back on.

Any thoughts would be greatly appreciated.

 

The bad booster will let air in and reduce vacuum. Which could turn the light on, through that little thing up on the fenderwell that the vacuum line runs to. My lights stay on, the nipple broke off that thing, and I plugged it off. When I was doing the booster, the light went off when I held the hose to it.