Brake Warning Light
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Tuned
Joined: Mar 2011
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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??
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Tuned
Joined: Mar 2011
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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.
Post Fiend
Joined: Mar 2011
Posts: 8,501
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From: Lynchburg, VA
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.
My automotive knowledge is mostly textbook so I cant say for sure, but Im sure proportioning valves can go bad.
Senior User
Joined: Mar 2011
Posts: 122
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From: Rush City, MN
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.
Humid air is a hell of a thing.
Humid air is a hell of a thing.
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Tuned
Joined: Mar 2011
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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!
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Post Fiend
Joined: Mar 2011
Posts: 8,501
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From: Lynchburg, VA
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
Senior User
Joined: Mar 2011
Posts: 122
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From: Rush City, MN
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"
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Tuned
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LOL, I know that feeling ALL too well!
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
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.
(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.
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