Brake Warning Light
 

Ok, my brake warning light is on. I have a full master cylinder, and the brakes seem to be working fine other than the warped rotors, which is being corrected tomorrow. What causes that thing to come on? I'm guessing low fluid could be one of the causes, but like I said, I'm not low. What else could it be so I can take a look while tearing into it tomorrow??

light come on when there is a leak in the system,check the hose,lines front n rear brakes out

If I had a fluid leak I wouldn't have a full reservoir and a firm pedal.

The light comes on when there is a difference in pressure between the 2 brake systems. Perhaps theres a problem with your master cylinder or proportioning valve?

Thanks. I knew it wasn't a leak. I've driven this thing a few hundred miles so far in a lot of stop and go without losing a drop. The PO said he put in a "new" master cylinder, but judging from the rust, I'm thinking his definition of new was far different from mine. Do the proportioning valves go bad?? Seems like a pretty simple piece of equipment so I can't really see it going bad. I think I'll pick up a master cylinder rebuild kit tomorrow and do that while I'm changing the front pads and rotors.

Yeah, it was probably a junkyard cylinder.

My automotive knowledge is mostly textbook so I cant say for sure, but Im sure proportioning valves can go bad.

Not necessarily. I bought and installed this new master myself, last summer. By looking at it, you'd swear it was older than the truck.

http://i85.photobucket.com/albums/k6...3-25213532.jpg

Humid air is a hell of a thing.

That's just horrible. I know companies try to keep costs low but man, powdercoating isn't expensive and it would keep their product looking good. Heck, a decent paintjob would help keep it from looking like that!

Geez. Come to think of it, the newish master cylinder in my Plymouth project looks equally as rusty.


But brake fluid eats through paint like a fat kid through cake. One spilled drop and the paint would be screwed. One would think that they would use some rust preventative coating though

Yeah, I know. It's my own d**n fault for not painting it before I installed it. I always think about it when I'm installing a bare metal part, but then I get the "F-it, I just want to get this installed and working"

LOL, I know that feeling ALL too well!

The brake warning light is a ground-out switch. There are three items that trigger the switch:

(1) Pressure differential between the front and rear brake circuits.
(2) Prove-out from the ignition switch (when you turn the key, just before the motor cranks, to let you know the bulb works)
(3) Faulty proportioning valve switch (grounding internally)

If your brakes are in great condition (no loss of fluid, firm pedal, satisfactory stopping power) then #1 is least likely. However, it still would not hurt to inspect the entire braking system for leaks, and to make sure none of your brake hoses are expanding under pressure. #2 is also not likely. #3 is the most likely; as this is a common problem. However, you'll want to visually inspect the proportioning valve to make sure no fluid is seeping from the threads of the switch.