Brake light on and off.

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surfaaron

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My red brake light is coming on and off. It wont come on if the car has been sitting for a while(over night) but after driving for a while it will shine bright, but then might just go off. I have blead the brakes and it still keeps happening. The pedal is a little soft and and does not feel as solid as 4 wheel disc brakes should. What do you guys think.
 
surfaaron said:
My red brake light is coming on and off. It wont come on if the car has been sitting for a while(over night) but after driving for a while it will shine bright, but then might just go off. I have blead the brakes and it still keeps happening. The pedal is a little soft and and does not feel as solid as 4 wheel disc brakes should. What do you guys think.
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The "Check Antilock Brake" lamp goes on when brake fluid pressure is dangerously low. You have only one or two hard-braking opportunities before you have no more power brakes.

There are lots of reasons brake pressure may be low.. The filter in the bottom of the brake fluid reservoir might be clogged up and fluid can't get into the pump (rare, but it happened to me) OR there could be a fluid leak somewhere.. OR the pump might be overheating because of a bad stuck-closed pump relay.. Sometimes it sticks and sometimes it doesn't stick. It's erratic. When the relay sticks, the pump overheats and then it won't pump for a few minutes while it cools.. meanwhile brake system pressure drops and the lamp goes ON. (this one also happened to me and other people around here..)

Do visual checks for brake fluid at all four wheels and around the master cylinder.
To check the filter, pull the hose off the bottom of the reservoir and fluid should stream out (have a towel handy).

As for the brake pump relay, the best test is to wait till you hear or feel the hydraulic pump running, like after you stop the engine.
Open the hood and tap the relay's protective cover with a screwdriver or something. If that immediately shuts off the pump, the relay's internal electrical contacts are eroded and are sticking..
That relay is in the black plastic box on the firewall behind the master cylinder on a Mark7
 
Upon re-reading your post, I see that I skipped over the word RED ...brake light.. so my previous post may not apply. If only the red lamp is lit and your amber "Check anti-lock Brakes" lamp is not lighting up, reaffirm this.

The red light means only that a brake is applied, as far as the car is aware... either pedal or parking brake.

That could be true.. A brake might be applied even though you aren't deliberately applying it. Something might be out of adjustment, or maybe there's a loose wire or similar

The manual has page after page of diagnosis if and when one OR the other OR both Brake-lamps are lit up, along with other symptoms that may or may not be present..

If you can describe everything that's going on, I can look it up, and might be able to narrow this down a little..
 
It seems like the red light is only coming on after I have been driving around for a while(hour or so). If it sits for a night or longer it will go off and then come back on after driving. It is only the red light. I have a manual for a 89 Markvll will it be the same for my 87 or at least close. It just seems like it is not building up enough pressure. Like I said before the pedal just seems soft. The accumulator comes on after you pressed the pedal down 3 or 4 times. LEt me know what you think. Also I can find no leaks.
 
Very weird.. symptoms are very similar to what happened to me at one time or another.

... and yet the Amber lamp doesn't light up.

Turn the ignition key to RUN. That amber lamp should light up.

If not, check the amber bulb. Put 12 volts on it. Replace it if needed.

If it's ok, put a multimeter (DC volt meter) on the bulb's contacts points up in the console and then turn the ignition key to RUN. You should see 13.2 volts or so..
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as for the manuals, yeah.. anything close to a 86-7-8-9 Mark7 manual should be close enough for this kinda work.. far as i can tell from hunting junkyard cars for parts, the brake system didn't change through the years.

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Every time you press the pedal, some hydraulic energy is lost (used). When pressure drops some amount, the pump kicks on. This is normal, and 3 or 4 hard pedal presses seems about right.
Under active braking situations, like stop-n-go traffic, the pump is more or less always running to keep pressure built up in the accumulator. Stop-n-go is where weaknesses are most likely to make themselves apparent.
 
The amber bulb is bad.Put a new one in and it glows bright as well. I had a issue with that bulb in the past were it would go and off at very random times and then it just stopped. I guess that is why. I checked all kinds of things when that was going on but never fugure anything out. That time it was just the ABS light not the red one as well. Am going to check around and see if I can figure anything out.
 
If you bled the brakes properly.. and there are no leaks.. there are not a lot of reasons why pressure would be low enough to activate the warning lamps.
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The accumulator ball stores pressure behind a gas, with a membrane between them. If this very simple device went bad it wouldn't be long before the ball completely filled with fluid and you would then have no brake pressure at all... never ever again. I think we can rule that out.
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Other than that, the pump might be starving for fluid and can only supply normal pressure erratically. Such starvation might be caused by low fluid levels, a clog in a feed line, etc. Aside from being obvious, a low fluid level would elicit a warning.
A clog would have to be searched for.

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Or, the pump may be overheating and shutting down, and you get periodic episodes of low pressure. The pump relay is notorious for causing this one. It's contacts stick closed, and the pump runs steadily for about 20 minutes (pressure is high all this time, and there are no warnings during this period.)

But eventually the pump's internal protective heat sensor shuts the pump off for about 5 minutes. Pump the brake at this point and pressure drops. There is no pump to restore pressure. The warning lamps light up.
The pump cools off and pressure is restored. Lamps go off.
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I'd first check that relay if i was you.
While parked, run the engine and pump the brakes until the pump goes on. Shut off the engine and open the hood.. wait a minute or so.
Does the pump go off or not? If not, tap the relay's housing. Does the pump immediately shut off? If so, the relay is bad.
 
I have bled the brakes but may not have done it right or enough. Key on and pedal down for rears and pump for the fronts. I have been puting a hose on the valve and puting it in a jar with fluid in it so I can do it myself without any help. Is this a bad way to do it. It doesnt seem to be able to suck any air in. The last time I did it the brakes really did not change a whole lot. I will try the relay. Let me know if I am bleeding them wrong. Thanks
 
You put the hose in a jar (submerged in clean fluid) and pump the pedal.. That's it?

That won't purge the line. It will pump fluid back and forth inside the line.
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Rears..
Key on (so the pump can go on and maintain pressure)
Open the bleeder screw.
Press the pedal about half way (This opens the master cylinder main valve.)
Let the fluid drain until it runs clear.. maybe 20 seconds or so.

Keep the reservoir filled.. check it often.

Fronts:
Key off.
Set up the hose and jar. Loosen the fitting 3/4 turn. Push the brake pedal to the floor and hold it there.

Have an assistant close the fitting. Slowly bring the pedal up. Wait 5 seconds.
Have the assistant open the fitting. Press the pedal to the floor and hold.
Close the fitting. Release the pedal.
Open the fitting. Press the pedal.
Repeat until the fluid expelled into the jar is clear and clean and has no air bubbles.

When you're all finished, close the fittings.

Pump the brake pedal several times to get everything seated and normalized. Press the pedal. See if it's firm or still soft.
Bleed again if it's still soft. Consider bleeding the master cylinder .. they can get air in the bore.. They have a bleeder fitting and are bled just like a wheel caliper is.
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I've done it by myself but it was a pain. I cut a piece of wood to length to hold the pedal down, jammed against the seat cushion, while I got out and turned the fitting.

I've also tried the cheapo "One man brake bleeding kit", but it's valve did not seal well, and it had a tiny bottle... and it was pretty much useless.
 
Come on! I am not that new.:D I guess I was not clear. I did it the way you are talking about but maybe not long enough. I will try it again and see what happens. Of course I got in this morning and the light is off. I also listend for the pump running and it is not. I will keep trying. Thanks again for all you help.
 
i kinda figured you were just being brief with your description of bleeding the brakes.. wasn't positive though..

Anyway, I don't mind writing instructions because it clarifies things in my head. I'll probably be able to bleed my brakes two years from now without forgetting anything..
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The relay won't always stick closed...

When it sticks, it tends to stay stuck until road vibration loosens it's contacts after brake pressure is built up and the relay's power has been disconnected.

Basically, you have to catch it closed when pressure is high and no power is flowing to the relay. If you notice the amber lamp on, that may be the best time to park, shut down and check it.

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While at first it was periodical and unpredictable, towards the end my bad relay would stick for a long time. It stuck closed through an entire trip to San Diego (500 miles down highway 5 in Calif.)
If i recall correctly, the warning lamps lit up around every 30 minutes and stayed lit for about 5 minutes. I timed it.
 
I am going to do a complete brake fluid flush on thurs and then go from there. I am also going to try to track down the wheel sensors and give them a cleaning. I have never cleaned them and I have heard they could make the abs light go on. Any help on where they are would be great and what to clean them with. Thanks guys.
 
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