No symptoms felt at brake pedal - still high pedal with very good resistance. No pedal softening at traffic lights.

Started car this morning and noticed the Brake Failure stayed illuminated for 5-10 seconds. It's never done that before. Then went off and didn't come on for the 18 mile drive to work. Went out at lunch and drove about 8 miles, everything normal. About 4 miles back toward work I'm driving at a steady speed and the light comes on - I didn't push the pedal and the light came on. Staying on permanently now, at least for the drive home.

Here is what I can say about the car and condition:
* I've owned it since new.
* Has good pads all the way around - I put them about 10k miles ago
* Rear pads recently developed a squeal
* Car still stops on a dime
* New master cylinder 2 years ago because the original was allowing pedal sink
* Original rotors with 200K - the fronts are straight but have significant wear, i.e. probably too thin but no evident problems
* Pedal is solid and everything feels good during depression
* The instrument panel has not been removed in the last 6 months.

So, usual suspect would be the master cylinder with an imbalanced equalizer valve, but I don't feel a problem with the pedal. Could extended piston protrusion in the wheel cylinder, due to thin front rotors, cause a fault light? What do you all think? R2

Hi there,

The clue you gave about it coming on without you touching the brakes is pretty con-clue-sive. The problem's in the device itself, like Ken suggests.

Did it rain? Foggy, misty, steamy this morning? Make sure the wire and boot are tight around the nylon switch insert and the wire forms a drip loop.
--
Art Benstein near Baltimore

The man who fell into an upholstery machine is fully recovered.

Weather was sunny, road was dry, car has been North Carolina all it's life so no corrosion.

Didn't know about the octopus - new terminology to me. I'll follow the wire and see what I can. Also will check fluid level for equality and look for any wet areas.

Follow the brake lines straight down from the master.

Here's a new one exploded. The pieces beginning with the black striped cylinder extending down in the photo are what light the light by grounding the wire attached. That cylinder is held in mid-position normally by spring tension (the one to its left) and pushed sideways if the hydraulic circuits are unequal.

The brass pin normally rests on the black stripe (insulator) but makes contact when the cylinder moves. The white nylon plug at the bottom holds the the brass pin against the moving cylinder with the spring and collar. The black ring just above the white plug is a dust seal - if brake fluid is leaking past that, then one of the small o-rings in the hydraulic part is probably hard or resting against rust.

Randy Starkie has a better photo showing how it goes together logically, but the principle is - it is supposed to be spring returned to center, meaning if the light comes on with no brake use, it is almost certainly corrosion has stuck the hydraulic parts or, as Ken found, created an electrical short.

I had one where the pin actually poked through the insulating layer (click for photo) at around 300K miles. I just reached in with a screwdriver and rotated the cylinder a bit. It makes sense to at least try to fix one of these without removing it because of the potential to mess up brake line fittings swapping all eight lines.

Another would get the light glowing (at various brightnesses) on wet days, as the wire had been disturbed from its drip loop position, leading moisture right into the switch connection.

Art, the exploded view photo is an excellent aide. I am embarrased a bit, because I had not checked the fluid level before B.C. reminded me - the simplest thing - and I found the front empty, just barely a covering of fluid over the bottom. With the strong pedal I've got I think I just snuck by without sucking air into the line.

Perhaps I upset the equalizing spool. However, the light didn't go off after topping the fluid off. I'll follow the lines down and check whether I've got wetness anywhere that I need to fix - then perhaps I'll try to rotate the spool with a screwdriver as you did.

Thanks for the picture and advice.

Even though the spool is spring loaded, the corrosion can keep it from recentering on its own. The way the light is supposed to work is only come on when you are stepping on the brake and there's an imbalance, going off again when you release the pedal. But crud can make it act more like the 140 version which did not self-return.

If you lost fluid, you've got a leak, no doubt about it. Sometimes they are hard to see at the calipers without a light and a powerful mirror. Nothing to put off too long, and don't give up finding the leak.

You shouldn't need to rotate the spool - that was for a different cause. If the switch is the leak, the octopus needs to be replaced.
--
Art Benstein near Baltimore

WARNING: The consumption of alcohol may cause you to think you can sing.

Finding that one compartment in the brake fluid reservoir is low enough, it is correct that air can get into the lines of that one circuit.

To extend the time before which you must repair the problem, keep that compartment topped up. BTDT Get a 32 oz and a 12 oz can of DOT 4 brake fluid. Keep the 12 oz can on board, and use it to add fluid. Refill it from the 32 oz can, which you keep in the garage or such. Reasons: Brake fluid eats paint. 12 oz can allows accurate pouring, but costs more per ounce that the 32 oz can.

Check the fluid every time you can, especially before starting up and when shutting down for the light. In a long resting period like over night, air bubbles in those two vertical lines can float up and into the reservoir.

I did this for over a month before doing the repair. Never a brake light or problem in stopping. Minor PITA.

Before attempting to remove the octopus, have a good flare nut wrench for those brass fittings. Craftsman from Sears, not their asian cheapies. Use a lot of P'Blaster, too. BTW taking a box-end wrench and cutting it to make a flare nut wrench won't work. The "circle" just opens wider. Steel forging not made to not be strong if not a closed ring.

Good Luck,

Bob

:>)

Check the fluid level in the master cylinder, see that the front and rear compartments have the same level.

If the levels differ, look for a leak. Check the octopus and all the calipers. On a calm day, you might smell the fluid.

The octopus has the switch that controls the warning light. If the pressure in one brake circuit is different from that of the other circuit, an internal piston moves and completes the circuit that lights the warning light.

So anything that causes the wire to the octopus to become grounded will light up the light. Your situation, with the light coming on without pressure in the brake system, points more to a wiring problem. Especially if the brake fluid level is OK and equal.

Check along the route of that wire to see if something has messed it up.

If the octopus shows a leak, go with the suggestion from Ken C. Fluid may show leaking around the wire harness connection, but the problem is inside.

Good Luck,

Bob

:>)

CHeck the calipers for a stuck piston. I had this once and that was the problem

Thanks, will be looking at calipers after I investigate the octopus route.

If there's really nothing otherwise wrong with your braking system, then the switch inside the "octopus" (i.e., brake pressure comparator, between the two triangular braking circuits) is probably corroded and shorting (grounding). It happened to me a couple of years ago (in my '84). There's a kit for its replacement: rebuild kit: 272702-2 ($36.23).
You can replace it while the "octopus" is still bolted in place (no need to undo all those brake lines) -- you'll need a small mirror (to see what you're doing, since you're working upside-down), some small needle-nosed pliers or forceps ("tweezers" if you're not a biologist), and you'll need tall jackstands to work comfortably underneath your car.