'97 Taurus GL 147k: Brake Light ON

[Colt Hero]

Brake light has been ON for a while now. I've checked all the brake pads on all four wheels and they're nice and thick. No visible leaks anywhere that I can see near each wheel or in the engine compartment. Fluid level in the Master Cylinder MIGHT be on the low side, I'm not sure. Looking in, the level is about two inches below the lip and at least an inch below the MAX line on the side of the reservoir. Any other reasons the light might be ON? Maybe it's the Emergency Brake? A bad sensor of some kind? Everything appears to be working fine. Brake works fine, Emergency Brake works, etc. Should I just pour some DOT-3 in and see if that makes the light go out? If it does, then I've got an invisible leak somewhere...

[Davescort97]

Yes put some fluid in the master cyclinder. There is a float in there that sends a signal to the light on the dash. I would fill it pretty close to the top. When the emergency brake is on the brake light on the dash comes on also. If you remove the console you can get to the switch to the light on the dash. You might have a leak but that chance is small. As the brake pads wear the piston automatically adjusts for that wear. As the piston moves out this causes the level of fluid to go down in the master cylinder

[shorod]

Colt Hero, are you serious!?! Two inches below the lip of the master cylinder? That's got to be nearly empty! Yeah, put some fluid in, pump the brakes a few times (without driving the car), and inspect for leaks. If it's really 2 inches below the top of the master cylinder, maybe you don't see a leak because there's not enough fluid to leak.

-Rod

[Colt Hero]

Gentlemen,

Bought some SuperTech brake fluid on the way home last night (12 oz, $1.00), and after reading your posts a few minutes ago, left the computer running and went right out and poured in the fluid! Looking into the filler neck of the reservoir, there are two (~1" long) vertical slots channeled into the wall of the neck and one (~ 1/2" long) vertical slot centered between these two slots. The fluid level was low enough to be below all three of these slots (although I think all three slots are at the same level along the bottom). Ended up pouring in half the container (~ 6 oz). Turns out there was a dirty "ring" around the reservoir neck about 3/4" from the lip, so I filled to this level (figuring that's where it most likely WAS). Now when I shake the reservoir (gently), I can see the fluid swishing around at the MAX line.

Next I drove the car around the neighborhood, pumping the brake pedal 3 times every 200 ft or so.

The light is definitely OUT! But I can't say anything more! The brakes still feel the same (fine) and I don't see any leaks anywhere! So where did the fluid go? Most likely it's going to be the (original) Master Cylinder, right? But the engine compartment appears dry all around it with no noticeable leaks around any of its tubing! Can it leak microscopically??? As I said, the light originally came on 14 months ago (actually longer than that - looking at my records, I changed the rear pads last on May 6, 2006, so the light came on just before that). So it's been ON for 17 months!!!! The fluid leaked somewhere (very slowly) over a 17 month period with no discernable performace degradation in the brake system!!!

[shorod]

If the master cylinder is leaking and you don't see it, then it could be filling the brake booster, and you will probably start to find brake fluid coming into the cabin where the brake pedal linkage is.

Otherwise, you may want to check the brake pad thickness again. Are you sure you were looking only at the thickness of the friction material rather than the thickness of the backing plate? You've either got to have a leak, or the caliper pistons/wheel cylinders are out so far it dropped the level in the master cylinder considerably.

-Rod

[Colt Hero]

Shorod,

Right now, my REAR pads have 17 months and 17k miles of wear on them and my FRONT pads have 23 months and 23k miles of wear. Looking at my records, on my last pad replacements using the same brake pad (Duralast from Autozone ... free replacements), I previously got 30 months and 33,184 miles out of my REAR pads (changing them prematurely as it turned out b/c the brake light never went out), and 39 months and 43,657 miles out of my FRONT pads. The current pads aren't anywhere near these numbers. The REAR pads are halfway and the FRONT pads are a little more than halfway. I physically pulled the FRONT pads out of the calipers (on one wheel at least) and they were very thick, so I think the pads are OK.

I'll look around the brake pedal inside the cabin for fluid from the power assist. Hadn't thought of that as a possibility.