Brake Light "On"
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New User
Joined: Sep 2006
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Brake Light "On"
OK, I've been on a rage bringing my "new" '85 F-350, 4x4 back from the grave. New hoses, belts, radiator, vacuum pump, rebuilt C-6, glow plugs, O-Rings for the injectors, filters and a bunch of other peripheral stuff. I'm getting alot of satisfaction doing this as well as relaxation.
Now the brakes....
I replaced the rear shoes and the front pads along with the master cylinder. Bled the entire breaking system (I thought) twice including inspection at the master cylinder and each wheel and I can't seem to find the problem. (There are no leaks that I can find nor brake fluid markings on my garage floor.)
The brake pedal is slightly soft in my opinion but not anywhere near the floorboard...and there's plenty of fluid.
The light originally came on after driving roughly 1 mile and has been on ever since.
OK, I admit I'm making a rookie mistake but I'm not sure what else to do.
Thanks in advance...
Now the brakes....
I replaced the rear shoes and the front pads along with the master cylinder. Bled the entire breaking system (I thought) twice including inspection at the master cylinder and each wheel and I can't seem to find the problem. (There are no leaks that I can find nor brake fluid markings on my garage floor.)
The brake pedal is slightly soft in my opinion but not anywhere near the floorboard...and there's plenty of fluid.
The light originally came on after driving roughly 1 mile and has been on ever since.
OK, I admit I'm making a rookie mistake but I'm not sure what else to do.
Thanks in advance...
Hotshot
Joined: Feb 2004
Posts: 11,697
Likes: 3
From: Marengo, Iowa
Check the parking brake... it also has a switch to turn the light on. Mine likes to come on periodically, and my brakes are solid, and the parking brake isn't the cause... then it will go out on it's own...
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
The vacuum sensor is located on the passenger side inner fender well.
Looks like a small tuna can sitting on the side, has a vacuum line and about three wires in the electrical connector on it. Turns the brake light on if the vacuum goes away so you know that braking power is greatly reduced.
Also there is a valve mounted on the frame under the steering column that will divert brake fluid away from either end of the truck that has a broken line on it.
When you were bleeding the brakes you possibly shut off the brake lines to either the front or back of the truck, which means you did not completely get all the air out of the lines.
The only way to reset the valve is to bleed the opposite ends a couple times till it resets.
I had trouble with mine one time, I had to open the bleeder and make hard sudden stabs at the brake pedal to get it to reset.
Looks like a small tuna can sitting on the side, has a vacuum line and about three wires in the electrical connector on it. Turns the brake light on if the vacuum goes away so you know that braking power is greatly reduced.
Also there is a valve mounted on the frame under the steering column that will divert brake fluid away from either end of the truck that has a broken line on it.
When you were bleeding the brakes you possibly shut off the brake lines to either the front or back of the truck, which means you did not completely get all the air out of the lines.
The only way to reset the valve is to bleed the opposite ends a couple times till it resets.
I had trouble with mine one time, I had to open the bleeder and make hard sudden stabs at the brake pedal to get it to reset.
Senior User
Joined: Jul 2006
Posts: 129
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Originally Posted by Dave Sponaugle
Also there is a valve mounted on the frame under the steering column that will divert brake fluid away from either end of the truck that has a broken line on it.
When you were bleeding the brakes you possibly shut off the brake lines to either the front or back of the truck, which means you did not completely get all the air out of the lines.
The only way to reset the valve is to bleed the opposite ends a couple times till it resets.
I had trouble with mine one time, I had to open the bleeder and make hard sudden stabs at the brake pedal to get it to reset.
When you were bleeding the brakes you possibly shut off the brake lines to either the front or back of the truck, which means you did not completely get all the air out of the lines.
The only way to reset the valve is to bleed the opposite ends a couple times till it resets.
I had trouble with mine one time, I had to open the bleeder and make hard sudden stabs at the brake pedal to get it to reset.
Thanks, 93
Elder User
Joined: Sep 2006
Posts: 588
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This has happen to me...on my 86
-it is possible when you bled the brakes the valve piston in the master cylinder has moved to the low pressure area...this is the safety feature on our MC's. When this valve moves, front or back, the brake light comes on.
-easy fix, reqiures some one pushing the brake pedal, the other cracking open the oppisite brake line on the MC...moving the valve piston back the center in the neutral position.
Pick your self up a Haynes [?] service manual...it explains in detail of why and how to fix problems such as this, lol.
-it is possible when you bled the brakes the valve piston in the master cylinder has moved to the low pressure area...this is the safety feature on our MC's. When this valve moves, front or back, the brake light comes on.
-easy fix, reqiures some one pushing the brake pedal, the other cracking open the oppisite brake line on the MC...moving the valve piston back the center in the neutral position.
Pick your self up a Haynes [?] service manual...it explains in detail of why and how to fix problems such as this, lol.
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Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
I believe if you push on the brake pedal hard and quickly the piston will reset to center automatically..........search out proportioning valve and differential valves.
http://auto.howstuffworks.com/master-brake2.htm
http://auto.howstuffworks.com/master-brake2.htm
Last edited by PLC7.3; Nov 17, 2006 at 10:10 PM.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
On my 86 the brake lines from the master cylinder go straight down to the valve as their first stop. that is where the front brake line gets split into two lines, so it has two lines in, three lines out for a total of five brake lines and an electrical connection on the top in the center.
If you blow a line and have your foot down on the pedal hard when it blows, it is like the piston gets stuck. The pressure has to be applied to the reverse side to get it unstuck. Had this happen one time when a fire truck came blowing through a red light at a blind intersection right in front of me, boy that was close. Heard the sirens, but in the middle of town with all the buildings could not see it till it was right in front of me in the intersection.
If you blow a line and have your foot down on the pedal hard when it blows, it is like the piston gets stuck. The pressure has to be applied to the reverse side to get it unstuck. Had this happen one time when a fire truck came blowing through a red light at a blind intersection right in front of me, boy that was close. Heard the sirens, but in the middle of town with all the buildings could not see it till it was right in front of me in the intersection.