I have no idea what to look at or how to look at this problem so here goes. One day after coming down a rather steep hill, my brakes got a little, ok a lot hot. Happens with an automatic sometimes. Ever since then, my brake and rear antilock warning light have been on and i dont know what it is. I have new brakes on it and its full of fluid, so i dont know what else to really look at that causes the brake light to come on. Thanks for the help.

oh yeah, i guess this helps, its a 1987 F-150 4x4 with 302 running gear and an AOD transmission.

 

If the brake light is on, it's more than likely a problem in the brake system itself and not the ABS system. Anytime something kicks that brake light on (except the parking brake), the ABS is disabled.

I would suggest you check your fuses as well as the brake fluid level sensor that's on the master cylinder reservoir. If it's neither of those, we can troubleshoot from there.

 

the fuses are fine, how do i check the brake fluid level sensor?

 

Disconnect the plug that goes into the bottom of the master cylinder reservoir. Then you can short the wires together there at the plug. I took a paperclip and bent it to where I could short the two wires together in the plug.

The book I was working off of said that two of the wires going to the plug are purple with a stripe, yellow, I think. If you have that, then short those two together. On mine, there was only one purple wire, a black wire, and a brown or tan wire. I ended up shorting the purple and black together to get the light to go away. It doesn't hurt anything to try shorting the wires together. You're not going to blow anything up.

This sensor basically shorts those two wires together and when there's a problem, then it connects those two over to the third one, which should be ground. This is done via a reed switch, I think. There's a magnet in the bottom of that float that's inside of the reservoir. When that magnet gets low enough, it causes the reed switch to close, turning on your brake light on the dash.

If this doesn't help, let me know and I'll dig up the troubleshooting diagram that I was working off of so we can proceed from there.

 

ok, thank you for the help, it worked shorting those wires together. now to fix the problem, do you think the sensor is bad, or the magnet inside the reservoir is knocked out of place? thanks Z

 

Pull the sensor out to test it. It's kind of a pain to get out, but it can be done. There's a little tab that locks it in place on the bottom side. Once you have it out, plug it back into the wiring harness. If your light goes out, then that means the magnet's at the bottom of the reservoir. If that's the case, buy a new reservoir. Autozone charges like $12 or so, if I recall correctly.

If the brake light's still on, then it's the sensor. I couldn't find any auto parts stores that carried the sensor. Ford might have them, I didn't even bother calling them. I went to the junk yard and pulled a couple from some old vans. If you wanted to test them before pulling them, you could bring a multimeter along with you. You should be able to find any of the two wires that normally don't conduct, and then push the float to the bottom. When you do that, they should conduct. That tells you that it's good. I just took my chances and grabbed a couple, keeping the one that looked to be the least rusty inside. Lucky me, they just gave it to me and it worked perfectly.

Good luck!

 

Downshift your automatic transmission for engine braking. On a really long hill with a heavy load it will make your transmission get hot. Keep clean transmission fluid in your transmission. There is a good article about how to change your transmission fluid in the tech section of this site .

https://www.ford-trucks.com/forums/s...d.php?t=335183

Here is a link that will lead you to more information on antilock brakes than you would ever want to know in case anyone needs it.

 

yeah i know how to do that, but my truck is so high geared that it just goes anyways. with those 3.55 gears in it, even when i pull it in first (which is what i did that day) it will still try and do 40 down a hill. and this hill isnt really long, maybe 3-4 miles, but it is about a 12% grade with switchback corners on gravel. thanks for the tip though.

 

The gearing would definitely make a difference and 12% is really steep but I wonder if your idle is too high or something. My truck has lower gears but it somewhat slows a 9000 lb trailer downhill.

I had an old jeep cherokee that had a neat feature, deceleration mode. Downhill at idle you could hear it when it shut off the fuel. Don't know if our trucks have any such feature.

 

They do. Above 1500 rpm, with no throttle input, the injectors are off. If you have a tach and downshift, you can feel them turn back on once the truck gets down to 1500 rpm.

Jason

 

Had the same problem with the abs light. Played with the float in the resorvoir as it seemed hung up and not sitting flat. Light went out and havnt had the problem come back.

 

yeah i found out it was the sensor on the bottom, got a new one from a junkyard and everythings alright now