Parking Brake Woes...

[soule64]

Hi. I sure hope somebody here can help. I normally hang out in the 67-72 section, but my son has a 76 C-10 that has a problem that I can't seem to figure out. (I did search the site before posting without much luck). Just out of the blue, the parking brake light on the dash came on and stays on when the parking brake is engaged or released. This light has never come on - with the brake on or off - in the three years that we owned the truck (I thought it was dead). I think 'Ok, no problem - there must be a switch that contacts the brake lever and it is now live'. I checked the schematic in the Haynes manual and it shows that the only circuit for the light goes thru the 'brake indicator switch'. But as hard as I looked - I could find no switch or wires anywhere near the parking brake. So then I am thinking 'well, maybe it is wired to indicate a fault in the system' and sure enough, one of the brake lights is burned out. After a few high-fives thinking that we solved the mystery, we replace the bulb... and the indicator light in the dash stays on. I did read a post on the site that said that the brake proportioning valve might be causing the light to illuminate, but I don't see how the light is wired thru it. So, my questions are:

1. Is there a contact switch for the parking brake? If so where would I find it? There is nothing in the manuals that I have. (a pic would be great because I have looked over the entire assembly!)

2. Is the "BRAKE" indicator light on the dash just for the parking brake ('on' when engaged, 'off' when released) or is it used for some other fault condition?

3. Is the brake proportioning valve somehow connected with the indicator light staying on? The brake lights (exterior lights) now work fine after I replaced the R/H bulb.

I apologize for the length of this post and the fact that I have probably over-analyzed the problem, but I feel like an idiot for not being able to fix it. Any help or suggestions that anyone might be able to provide me and my son are greatly appreciated. Thanks.

[D13]

The prop valve has a switch that will turn on the light if the valve is off center. The brakes may seem to work fine even with this condition. This is fond of happening after rear brake work, or after a very hard apply.
There should be a switch on the park brake assembly that also will turn the light on. For many years we roped the pedal up to the vent pull rod to keep this turned off (after the park cable froze). Quick check- with the light on pull the park brake pedal up. If the light goes out that's the place to start looking. If not, the prop valve or a short.

[soule64]

Thanks for the help. I think I understand it a little better now. I am still not able to find the darn switch on the brake assembly though. PO might have removed it, I suppose... The manual says brown or brown/white wires but those are MIA also...

[wedgemon]

From the "FIRM GRIP OF THE OBVIOUS" files . . .

Check the fluid. Low brake fluid will set off the light, too.

Just thinking.

- Dave

[soule64]

Wow. Bad case of tunnel vision on my part. I did not check the fluid. I was so consumed with the electrical stuff. Time for a 'could'a had a v-8' smack up side of my head...

[LONGHAIR]

There is no fluid level indicator light on a truck that old (76). That dash light should be controlled by the E-brake pedal and the proportioning valve.
As mentioned, on a truck this old, the previous owner could have removed the original E-brake wires/switch.
From a "testing" standpoint, you could disconnect the wire to the proportioning valve, to see if the light goes out. If it does, you have other issues. Don't leave it unplugged and ignore it!
If the proportioning valve is indeed causing this, you probably have a rear brake problem/leak. They don't just "pop" for no reason. The pressure is not balanced between the front and rear. It is usually "low pressure" in the rear. Excessive pedal travel from improper adjustment can cause this, as well as air in the lines, or lack of fluid.
It can be a challenge to get it back centered and working right though.
You have to check for leaks first, be sure of adjustment second, and bleed last. Many times you will have to "balance" the pressure by opening a front bleeder and taking some of the pressure away from there.
If that was the case, you would then have to bleed the entire system.
Once you get the light off, gravity bleeding is your friend. Open all 4 bleeders and just let them flow, don't thouch the pedal at all. Be sure to keep the master cylinder full, while you do this. This will flush out some of the old fluid and equally bleed everything. After all of them run freely, close them up and top-off the master cylinder.....done.

[soule64]

Thank you for the advice, This is what I love about this site - tons of knowledge and information. I checked the master cylinder and it was full. I'll work on it tomorrow and see what happens. Thanks again.