Okay, this might be a quick and easy question. I noticed my brake pedal was mushy yesterday morning. I thought it was just worn pads, maybe. Then on the way home in the afternoon the Emer Brake light was blaring red at me. Nope, the Emer Brake was not applied. I never use it.(shhh...don't tell.) I pulled over and put the truck in park. Then I activated and released the Emer Brake foot pedal. It doesn't really work, so I had to pull it back up with my hand while pulling the release handle. The light was still on. Then I put the truck in gear and the light went out. But 10 seconds later was on again. If I let off on the gas the truck idles and rolls like there is no brakes applied, so I think the front and rear brakes are not engaged. Also, another tell tell sign is that there is no smoke, excess heat, or smell of burning brake pads when I pull over. And when I let go of the wheel it does not appear that the truck prematurely slows or pulls to one side. So I'm leaning towards a faulty Emer Light switch. That's the first time it's been on since the 5 years I've owned the truck. So my question is is the Emer Brake light tied to the foot activated pedal? If so, I should be able to just get up under the dash for further troubleshooting. I'm hoping it's not somehow tied to the transmission switch or rear end. I haven't had time to look at it. I plan to troubleshoot it this weekend. Just need some ideas of where to look first. Thanks.

 

The brake warning light works off of the emergency brake and the brake proportioning valve. if either trips the switch the warning light comes on.

I would lean towards the cause of the mushy pedal is making the light come on......hey the system must be working!

 

I believe that if you are talking about the red "BRAKE" warning light on your instrument cluster of a 73-79 F-series truck, the only input it has is the switch from the proportioning valve bolted to the frame on the drivers side of the truck. The light is not supposed to light when the "parking brake" is applied, unless someone has installed a switch on the "parking brake" pedal, as I have done. I would think if you have a light coming on you have some trouble with fliud somewhere, which explains the mushy brake pedal feeling. I would look very close at ALL brake lines , hoses, calipers, wheel cylinders, master cylinder, proportioning valve, etc... for a small leak. sure sounds like thats the trouble to me. -Ed

 

Oh Crud!!!!!! Glad I asked!!!! I guess it's a Brake Warning light, and not a Emer Brake light. (It's on the right side of the dash.) That would explain why it's so bright red---to tell me to look at the brakes. I guess I won't put that off for too long. Wish me luck.

 

We have dis-counted there being an Emergency Brake Light numerous times.

The brake FAILURE system light will definitely be set off by a a leak in the system....... it can also be set off by low pressure (fluid by-pass) from one circuit of the master cylinder.

The fix info is on quite a few Brake failure light threads

 

The light is triggered by a pressure difference between the front and rear systems.
If there is a leak or to much air in one of the systems there will be pressure difference between the systems (which usually is bad)and the light will come on.

I had a small leak in a wheel cylinder on my truck and the light would come on when i hit the brakes.

 

look into the master cylinder you will see one chamber is probably low or out of fluid thye big resivior is front brakes the small is read brakes sometimes if your rear adjusters freeze up and when you apply the brakes it pushes the wheel cylinder cups out

 

Very wrong answer!!! Do not under any circumstances drive this truck at all until it is fixed. What you have described is brake system failure. Don't even take this truck to get the parts you need.

Odds are the problem is in the master cylinder but it could be a leak elsewhere. Trouble shoot this thing now. If you can't find a leak elswhere (line, fitting, or wheel cylinder) then it's the master cylinder. Many times these fail and leak into the power booster. If this is the case pull the booster and drain the brake fluid out of it while you are working on it.

Remember your brakes don't have a problem. They have FAILED!

 

Don't forget that brake fluid is corrosive. If your master cylinder is leaking into the brake booster be sure to clean it out well or else it canl eat the seals and metal inside the booster. I had this very thing happen to me, I put it off too long and just about hit someone. When I took the master off the booster was full of fluid, I pulled it off, and used an entire can of brake clean (spraying it in and shaking it around, pouring it out, repeat until clear) and let it dry out for a few hours before putting it back together.

 

Thanks all. I made it home ok. (I know...tempting fate.) I checked the fluid reservoirs and they were full, so I'll be purging all the fluid and lines tomorrow. Hopefully it won't be something major. I just replaced that booster and master cylinder less than two years ago. I wonder about that brake proportioning valve. It's all crusty and looks like oem. We'll see what I find out tomorrow in the daylight.

 

Very odd. No leaks on the external master cylinder, booster, lines, proportionining valve, or on the back of the brake backing plates. I even cleaned the proportioning valve with carb cleaner and a tooth brush to make sure there were no hidden leaks. Then we bleed all the lines and topped off the fluid. The only odd issue was the left rear lines did not purge any fluid when I loosened the bleeder valves. It took two or three foot pumps on the pedal for that line to spew any fluid. Looks like it might have been air in the line? Anyway, we purged all the dirty fluid and air bubbles. And the light went away and the brakes are back to normal for now. I will keep an eye on it and we'll see what happens.

 

Did you pull the rear drums off and look at the wheel cylinders? If it's not dry in there you have a leak.

 

Nope, didn't pull them. I did not see any liquid externally so figured they were still working properly. I just replaced them about 3 yrs ago, but to ease my mind I think I'll pull all four wheels this weekend and check the cylinders and calipers.