Brake Issue Question

Summary: I think I may have sucked some air into the ABS system of my Chevy Astro. Brakes appear to be functioning properly but I am getting intermittent warning lights. I plan to bleed the brakes, but don't know if I need to do anything special for the ABS system.

Full story: Driving the Astro across country, the ABS and "Brake" lights popped up on the dash. Turned out the fluid in the reservoir was really low (stupid me inspected pads, rotors, and lines before leaving but not fluid). Topped up reservoir, double checked for leaks, and didn't find any. Light came back on the next leg, but went off again the next time the car was restarted, and stayed off for a while. A couple days later, and it came back on again. Checked brake fluid, and it is up where I left it. If it is leaking fluid somewhere, it is very slow. No issues with the brake pedal feeling weird or sinking to the floor or anything. The light comes on when just cruising and not touching the brakes at all. Then stays on until I shut the car down. The brakes do not feel any different with the light on or off, but I have not tested to see if the ABS will cycle or not with the lights on. My best guess is that the low fluid level sucked a bit of air into the ABS system and is making the computer whig out.

Did you figure anything out? I know that some vehicles need to be bled in a special way because of the anti-lock valves and pumps but that doesn't seem to be the problem with yours. The air causes a soft peddle, not trouble lights as far as I know. Some vehicles turn the anti-lock light on any time the brake light is on which is stupid. Check your emergency light switch.

Pull the drums off and have a look, I'm betting wheel cylinder.

don't see how this will help, but I'll leave it anyway …

when I change pads on the CRX (or anything else for that matter) I open the bleed valve to help push the piston back (+ it gets rid of the "bad" fluid that's at the caliper itself) … on occasion I've forgotten to check the MC and re-fill it .

especially out on track, under heavy braking and certain cornering loads the brake light on the dash would come on … I'd come in and face palm, and then top off the MC, even though it was above the min. level … in my case I've found that the CRX is very finicky about how much fluid is in the MC … i.e. it has to be right at the upper limit …

wbjones wrote: especially out on track, under heavy braking and certain cornering loads the brake light on the dash would come on … I'd come in and face palm, and then top off the MC, even though it was above the min. level … in my case I've found that the CRX is very finicky about how much fluid is in the MC … i.e. it has to be right at the upper limit …

Good point. It's not a problem specific to the CRX, or technically a really big problem. The purpose of the warning light is to say "WARNING THE MC RESERVOIR ISN'T TOTALLY FULL, GO CHECK!"

My Samurai gives a brake warning in hard right turns if the MC isn't totally full.

If you have access to one, a pressure bleeder will likely do a good job at purging air from the ABS pump. I've also heard, though I haven't had occasion to try it myself, that repeatedly engaging the ABS through hard braking will often purge air that's gotten trapped. Obviously you'd want to make sure the reservoir is topped off before attempting this.

to the OP: your best guess is wrong.

srsly though, the ABS unit is a flow-through device under all conditions EXCEPT when you're actually in an ABS event. so just letting the MC get low will not suck or trap air in the ABS unit.

is the current situation that you occasionally get BOTH the yellow ABS light and the red BRAKE light together? or do you sometimes get one without the other?

I have had to replace ABS units when nothing is physically wrong with anything. I am willing to bet nothing that the ABS is just used up and needs replacement.

I get both lights on my Malibu from time to time. One of the cheapie hub bearing's abs plugs gets corrosion inside it. A quick cleaning makes it go away for a couple months.

I remember my last GM product, and come to think of it, only car with working ABS, having about 7 bleed screws coming out of the unit.