Imma tinkin it's a short in the dash area, or possibly around the e-brake switch. Could also be a short under da hood where the brake switch is, but...the on for a minute and then off stuff makes me think it's(the problem) INSIDE the cabin somewhere. I think I would unplug both the e-brake switch and the underhood switch, and see if the light still comes on...if so, then it would be time to start tracin wires, starting from the e-brake switch...

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Joel Adams
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I agree with Joel.  If disconnecting the two wires does solve the problem, reconnect one of them at a time to verify which circuit.  One possibility is the proportioning valve, which contains a switch that senses uneven pressure front to rear.  That is where the wire under the hood connects.  You might actually have unequal pressure, or the sensor might be bad.

Larry

Thanks for your ideas on this!

It is normal for the light to go on durning startup, but not to remain on for longer than about thirty seconds.  Thats the problem with intermittred problems.  Hard to diagnose.

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So, my mechanic had what they're calling a "minor" heart attack. If all goes well he'll be back on his feet in 3 weeks or so. He's a good guy, keep him in your prayers.

May have been a peice of dirt or foreign matter that cause the light to come on.  When you bled the brakes, you swept away the problem !!  Maybe.

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Your original description seemed to point to an electrical malfunction, since using the brake pedal made no difference. Normally, if there is a problem with the P-valve switch, pumping the brakes will make a change. There might still be a problem with the switch on the p-valve(or the valve itself), since bleeding the brakes turned it off, at least for the time being.



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Joel Adams
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I'll be paying close attention to that darn brake light and how the pedal feels for a while.

Well, the darn brake light has reared its ugly head a few times more. The pedal is still firm. KDADDY792009-10-24 10:34:18

The fluid will wind up in the booster, and eventually it will damage the diaphragm, as well as fill the booster with fluid, which will reduce the effectivness of the booster, meaning the pedal will get harder to push...
There is a seal between the master and the booster, but most of those by now are really nothing more than rubber dust...
Unbolt the master cyl, leaving the lines connected, and pull it forward, away from the booster. If it is leaking , it will be obvious.


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Joel Adams
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Hey Joel,

Well...iffin it were mine, I would most likely rebuild the master cyl meself, but I realize that's not an option for everyone. In that case, then you can buy a rebuilt master and install it.
The seal I mentioned above is not part of the master cylinder...it is part of the brake booster. It seals the rod on the booster that actuates the master. The outer part of the same seal also seals against the master cyl where it bolts to the booster, so, theoretically, there will be a tight seal so no vacuum leak occurs. However, if the booster seal is bad, AND the master is leaking, then the leaking fluid will go into the booster, since there will be vacuum pulling it in there. If the master is NOT leaking, and the booster seal goes bad, then it can pull fluid past the master cyl. seals, and create a leak there.

I had a vacuum leak on my '74 that I had a hard time finding. It took me several years to finally locate it(I don't drive the car much, so it wasn't exactly a priority). I finally discovered the seal on the booster was the culprit. The seal is not available anywhere, at least not that I have found. I wound up using a seal for the headlight actuator...worked poifectly!
If your master itself is leaking, it's time to either replace, or rebuild it, depending on you mechanical skills.
Adams' Apple2009-10-25 07:54:07

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Joel Adams
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We'll go with a new Master Cylinder.

Kevin, if you get new master cylinder, make sure you bench bleed it before installation.   

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Also, when replacing the master, be sure to check the depth of the piston hole where the push-rod goes into the master. There are two different depth piston holes for different year models. One is very shallow, and the other is quite deep. If you put a deep hole master on where a shallow one was, you won't have any brakes, since the push-rod won't be long enough to push the piston in the master.
If you get a shallow hole master, and try to put it on where a deep hole master was, it won't bolt all the way on without bottoming the piston in the master...in that case, you won't be able to push the brake pedal down.
I think most of the parts vendors have the dimensions listed...lemmie look and see can I get a pic to show what I mean...

Looks like the '77-'82 cars had the "shallow" piston masters. I remember one time I had rebuilt a master off of a friends '81 after I had replaced his with a reman. I kept the original one. Then, one day, the one on my '74 took a dump. I figured, "Hey...I got this one here that is rebuilt, so I'll just slap it on and go!"....NOT! Mine took the longer push-rod/deeper piston, and the later model was the short rod/shallow hole master. Sooooo....I had to rebuild mine...
Adams' Apple2009-10-25 08:20:29

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Joel Adams
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Bench Bleed --- Check

Well, it's done!

Was the old master actually leaking, tho?

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Yeah, it was a goner.