Hello,

I have been working on the brakes of my 76 F100 4WD. I rebuilt the rear drums, replaced the wheel cylinders and bleed the entire system. I left the front discs because they did not have much wear. After I was done, the "brake" light in the instrument cluster would not turn off, and the brakes were spongy and not working well. I bleed it more to no avail, and did what my manual said to press the brake pedal with the engine off and the key on to reset the light but it would not turn off. I admitted defeat and took it to the shop, they said they bled it and everything was fine, and the brakes now feel firm and stop well, but now I have no parking brake and the light was still on- the mechanic said the parking brake bracket was broken and it has a sensor that is the reason the light was on. Its not broken, you just have to hold the release lever up when you put the parking brake on, it just needed adjusted so I did that and it works fine now too.

But the "Brake" light is still on on the dashboard- can I reset this? I know its supposed to be an indicator of a problem, but everything seems to be working fine. Does anyone know what the problem could be?

sorry for the novel, and thanks so much for any insight/advice

Matt

 

That light is telling you that the Parking/Emergency Brake is engaged.

Unk Bob

 

The "Brake" lamp on the dash is associated with this:

C8AZ-2B264-A .. Brake Pressure Differential Valve Warning Lamp Switch / Obsolete ~ available NOS & from auto parts stores.

1968/69 FoMoCo Passenger Cars; 1968/79 F100/350; Bronco & Econoline.

This switch is a notorious POS! It threads into this valve (that some people call a proportioning valve).

*Parking brake signal switch only available for 1973/79 cars. Not available for F150/350 & Bronco until 1984 (no F100's after 1983).

 

If somebody finds a tricky way to rig it to work with the parking brake, post a diagram! I've been thinking about it for quite a while, just another minor project WAY down the list........ Should be as simple as a switch with a relay and some fancy wiring.

 

Prop valve 76' f250

There's a little more to the light than that, it is also tripped by the Proportioning valve if fluid pressure pushes back on the internal spring/valve giving the driver a warning that there an issue with the system, or it can be a failed connection for the little plug in sensor , not sure which generation of valve you have, but you may have forced the valve to trip the sensor when you bled the brakes, do some googlin on it.... Some valves have a pin that needs to be pulled when bleeding, sometimes you need to screw in a 'stop' pin where the sensor goes, so the valve dosent move when bleeding or flushing the brake system..... Im in the process of installing a new valve and bleeding everything ...


In that pic my sensor plug in is hanging un hooked to the left, cuz im replacing it with a new one for that new prop valve, it plugs into a hole in the center of the valve in between the top two lines..

 

OP has a 1976 F100 4WD

D5TZ-2B257-B .. Brake Pressure Differential Valve-Use with disc brakes / Marked: D5TA-2B524-FA or FB / Obsolete

1975/79 F100/150 2WD/4WD / 1975/79 F250 2WD with single piston caliper disc brakes / 1976/79 F250 4WD, Bronco & E100/150 / 1979 F350 4WD

 

Your "mechanic" is an idiot and should refund your money.

The brake light on our trucks has absolutely nothing to do with the emergency brake.

The brake light is a self-test of the braking system. In a well-functioning vehicle, the light will flash momentarily upon startup as it performs the self test.

The brake light is wired to the "proportioning valve". If the check-ball moves from its center location to either the front or back, the warning light will remain illuminated.

The valve has a "****" that must be either pushed-in or pulled-out (depending on GVW) when you bleed the brakes.

I must say, however, I've bled the brakes on all three of my trucks without touching the valve, and they came out fine.

Check the "read me first" threads at the top of the page for a full write-up on the valve and the reset procedure.

 

There are bleed tools to help keep the warning switch cylinder in place while bleeding. pending on the valve, the tool may need to be placed at the center top of the valve, https://www.ebay.com/i/152216419694?chn=ps&dispItem=1
or
at the end, Proportioning valve Tool J-22742 - The FORDification.com Forums
I hope this helps.

 

X2 on the e-brake and the dash "brake' warning light are NOT connected in any way. The light comes when when you have a failure in your hydraulic system like a big leak from a blown line.

GVW make the button push or pull.

 

The mechanic probably didn't know to 'activate' the bleeder valve or hold-off valve or whatever, and didn't get the fronts bled properly, causing a pressure differential in the system and triggering the light.
Another possibility is that if he's really bad, he might've messed up the switch - although when the switch breaks off, the warning lamp will still illuminate during prove-out, and then go out. But it won't illuminate if there does happen to be a pressure differential.

 

Thank you so much for the information. I definitely wont be going back to that "mechanic". I tried the reset procedure but it didn't make the light turn off. Is there a way to test if just the sensor or the proportioning valve is bad?

 

You dont even need the relay. I used a brake light switch, the kind with the threaded part and a little button that the pedal pushes in. I rigged it up so the park brake pedal hits it when the brake is up or released. It closes the switch when you step on the park brake and the button pops out. There may have been a hole in the bracket on my truck for a missing bushing or bumper, i cant remember, but thats where i put the switch. One wire to the dash for a ground, the other ran out the firewall and just spliced into the wire going to the frame mounted valve from above. You can tie in at the ignition switch too, theres a wire going to it so itll light up in the start position for a bulb test. Either switch can now ground the light to make it come on. Mine lights up now while cranking, if the park brake is on, or if the brakes fail.

 

Now the "brake" light goes on and off while driving- usually its on. Will the pressure between the front and rear brakes eventually equalize and the light will go off?