So I'm heading out from a friend's house when the guy in front of my decides to pull a U-turn. I follow, and bump just the front right tire over the curb (after all, I can nearly do a Uie on a two-lane road). It wasn't a hard hit or anything, but a few seconds later, the "Brake Failure" light begins to fade into view.

I pretty much freak out. I mean, brakes are important, and I know that replacing a master brake cylinder isn't exactly easy or cheap. So, I test out the brakes as best I can. They seem to be working well--there's no pedal sinkage (so cylinder is OK) and I seem to be braking evenly (so it's not stopping on three wheels). I follow my friend to where we're going, and the brakes seem to be working fine the whole time.

I park, turn the car off, and turn it back on. The light is now off. Okay.

I come back to the car an hour later or so, and the light comes back on when I start the car. D'oh. I drive home, and again braking seems fine. I park the car and it sits overnight.

I get up to go to work the next morning, and the light is still on, but I notice it's not that bright. In fact, I remember that it seemed to come on very dimly at first, and then eventually get up to what seems like maybe half power. Here's what I mean:



The Emergency Brake light is lit up on the left, and the Brake Failure light is on the right. It's much dimmer.

I start the car once or twice during the day, to run errands for work. When I get in the car at the end of the day, the light does not come on. It stays off for the ride home and has remained off since (as in, if I started the car right now, the light would be off).

I took the car to the mechanic's shop today because I had called them yesterday to make an appointment, when the light was still on. They checked out the car today, drove it, and took a look at everything.

The master brake cylinder will probably need replacing (that's another story), they say, before I go back to school in a month. Hoewver, as of right now, it is working as expected.

The rear brake pads are a bit worn and will almost certainly need replacing before school, but they too are currently functional.

The switch for the light, apparently, is fine, as when it goes "the light comes on and stays on," according to the mechanic.

Does anyone have any guesses as to why the light came on, and why it was so dim? I was thinking that there could be a short or accidental ground somewhere, but the mechanic nixed that idea. However, I *have* pulled the speedo cluster to install a new odometer gear. It is possible, though fairly unlikely (I think), that a wire could have worked loose.

Nothing else is giving me unexplained problems. Is the Brake Failure light on a single, independent wire? If it's on a half-moon type connector, then I don't see how there could be a loose connection without something else being disconnected too. Does anyone have any guesses as to what the problem is/was? Should I suspect problems, even though it seems the light won't be lighting up again any time soon?
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'89 244 GL -- 104,XXX miles (see profile for info on car)

If the light is on in the II position before starting the car and goes off when started then it seems to be working properly. If it is dimly lit sometimes while driving then maybe as you suggest "a short or accidental ground" could be the problem. Follow the wire from the brake line junction and see if it is grounding anywhere.

You say the your brakes work but "The master brake cylinder will probably need replacing (that's another story)", so what's the story? Ie. if the pedal isn't dropping on light pressure and your brakes work, why?

See http://www.brickboard.com/RWD/index.htm?id=839066&show_all=1
Similar problem?
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1980 245 Canadian B21A with SU carb and M46 trans

I think I'm having the same problem as the person in the thread you referenced. Somewhere there is likely a short.

The Brake Failure light, even if there is a "weak point" in the line, will still work properly, correct? The light has stayed off, and I'm hoping that's because the ground/short corrected itself, *not* because the line was severed completely.

I'll address the Master Brake Cylinder issue in another post. Briefly, my mechanic seems to be urging its replacement only because the shop will be replacing the rear brake pads at the same time. He is giving me the impression that somehow wear is correlated between those two items.
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'89 244 GL -- 104,889 miles (see profile for info on car)

I don't see any logical connection between rear brake pad wear and the master cylinder, either (though flushing the system at 100K might not be a bad idea). Ask him to explain!
And did you check whether the brake failure light comes on with the key in the II position, just before you actually start the car? That's why they all light up at that time, so you know the bulb is actually functional!

I'm almost positive that the light comes on in the "II" position, but I will double-check the next time I get into the car.

I don't see any logical connection between the rear brake pads and the Master Cylinder, either. I think that (1) they both happen to need replacing at the same time or (2) the mechanic wants to get everything done at once, while he's messing around with the brakes.

Though (1) is a distinct possibility, I suspect more that (2) is the likely situation. The Brake Failure light might have gotten him to thinking about replacing it, and so he wants to go ahead and do it while we're getting the pads done.

I've had no symptoms of a bad Master Cylinder, however, and so I don't see any reason to replace it, especially if it already has been done once (I need to look at our records). My fear is that my parents, being cautious and not desiring me to spend money on "extras," will force me to spend my money saved for a stereo instead on a new, unneeded Master Cylinder. I'll let you guys know what happens.
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'89 244 GL -- 104,894 miles (see profile for info on car)

You just need pads? Or are you getting caliper(s) changed?

If you're getting calipers, yes, it's logical to change the m\c at the same time. Then you only bleed once.
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'73 142, '75 242, '75 245, '80 245, '83 244, '86 244, '87 745T, 92 244 (for sale)

I'm not sure I agree with the mechanic on the Master Cylinder issue.

The rear pads shouldn't wear out as quickly as the fronts IF you replace them both at the same time. The Fronts should wear out first or almost equally even though the rear brake pads are smaller. Most of the braking is done with the fronts.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me

I would guess that the front pads have already been replaced, and now it's time for the rear ones to be replaced. I trust that there is sufficient wear to replace the rear pads, but I am obviously skeptical about the Master Cylinder.
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'89 244 GL -- 104,XXX miles (see profile for info on car)

Just for a reference, I have 250K on my volvo and I have the original Master cylinder. It's not really a maintainence part.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me

I'm too lazy to go pull a wiring diagram and study it, but I can tell you that, in general, a bulb lights dimly when something else looses its ground and ends up using the bulb as a route to ground, often via a round-about route.

It's pretty clear that the problem is not your brakes. I think that there are two triggers for that warning light - the fluid reservoir float switch and the switch that compares the pressure in the two brake circuits. You could pull out both those switches and test them, but I doubt you'll find the problem there.