wheelo90

Today upon driving my pickup, I was running a few errands for my dad and all at once my brake warning light is on. The brake pedal feels fine some times and other times, they are really soft (kind of like they need bled)

So, what does the brake warning light mean?
Also, when I bought the truck, the previous owner had put a peice of black electrical tape over the Anti-lock and the Brake warning light.
So My plan is to bleed the brakes, then see if the light goes off, if not should I disregard it?

Thanks!!
Wheelo

imabnormal

do not disregard it!

it (typically) means that your prop valve has shifted to one side or the other (front or back) due to a leaking line. it may, after some time, re-center itself causing a mushy pedal for one application of the brakes, then shift again, sealing the bad line off.

it could be the master cylinder (probably not), or anything downstream from it. or, it could be a bad switch, but given that the brakes don't feel right, they are most likely not right.

look for leaks, especially toward the back end of the truck.

imabnormal

if it is the master cyl, you will probably be able to push the pedal down and down, and down, etc with light pressure, but if you suddenly apply a lot of force , the pedal will not "slip" downward.

jrussell

Doesn't the light come on when you're low on brake fluid? I would check that first, but as imabnormal said, check the rest of the system because if it's low that would likely indicate a problem.

wheelo90

I had finished checking the fluids in everything last night( fuel filter and oil change, checked all fluids and topped off as needed)
The brake fluid level has not went down any, and I cannot find any leaks anywhere on the truck.
Thanks,
Wheelo

jrussell

Sticking E-brake switch? Mine sticks all the time.

edwinsmith

The self adjusters in the rears are notorious for sticking. If the backs are way loose it could make the light come on. If they're adjusted properly and you can't find any leaks suspect the master cylinder.

Also, the RWAL is a piece of junk. That's probably why the tape was over the anti-lock light. If it bugs you just unplug the unit which is behind the glove box. Many have tried and failed to make this system work right and wind up just unplugging it like I did.

Edwin

brainfade

Some info. The RWAL has a cylinder and piston arrangement sort of like a wheel cylinder with one end closed off. The piston is spring loaded so that it stays at the top of the cylinder under normal conditions. When the ABS computer detects wheel lock at the rear axle, it opens a valve in the RWAL and dumps fluid out of the rear brakes to this cylinder. That gets the wheels turning again, but reduces the rear brake effort so then you have to push into the pedal harder to maintain the same decel. When you release the brakes, the spring and piston push the fluid back out of the cylinder and back up to the master cylinder. Sometimes the valve that controls the fluid flow into the RWAL cylinder gets sticky or leaks. This will make the pedal drop and feel soft and turn the light on because the extra fluid needed to fill the RWAL is more than the master cylinder can supply. The master cylinder and propvalve see it as a leak. However, when you release the brake, the fluid is returned to the system so you will never see a leak or fluid loss. It can drive you nuts trying to figure it out if you're not aware of this little gadgets function. In addition, the problem may not be with the RWAL, the computer may be bonkers and randomly dumping fluid, the ABS sensor in the differential may be faulty and triggering the dump as well, or the valve may just be leaking internally. If you have the ABS and brake lights on, you may want to investigate the elctronics before you jump into the valve. Some guys have bypassed the valve and fixed the problem, but then you really need to install an adjustable prop valve so you're not sliding the rear tires all the time.