Brake warning light

[kellydw]

Hi All
Can't seem to get the brake warning light to go out. Have bleed the brakes several times and used the Chrysler manual method for bleeding and centering the cast iron proportioning valve - 73 Cuda with front disc and rear drums. Any ideas

 

[pschlosser]

Time to test the brake warning circuit and switch.

The brake warning lamp in the dash has two wires, one (dark blue) provides + voltage. The other (black) goes through bulkhead connecter terminal #12, to a switch below the master cylinder, in the engine compartment, and gets ground to illuminate the lamp.

There may be a short grounding this (black) wire, the safety switch is faulty, or something amiss in the proportioning valve. Try disconnecting the wire going to the switch, and see if the lamp goes out. If not, the switch may be fine, and you gotta look deeper.

Back in the 1980s, I drove a 1970 barracuda with a failing master cylinder for almost a year. The brake warning lamp would frequently come on. I could milk function from the master cylinder by pumping the brakes. In stop-n-go traffic, the lamp was on for long periods of time. At one point, the lamp stayed on. Even after repairing the master cylinder. After some troubleshooting, I found the black wire got too hot, (presumably) because the lamp was on for long periods, and the black wire melted its insulation and melted another wire to ground. The long and short of it is, I had to repair the wiring harness coming from the fuse bulkhead up to the instrument cluster to resolve that problem.

 

[kellydw]

Do you mean disconnect the wire going to the switch on the proportioning valve??? to see if t6he warning light goes out??

 

[Katfish]

Any chance the E brake is pressed, or issue with that switch?

 

[kellydw]

Do you mean disconnect the wire going to the switch on the proportioning valve??? to see if t6he warning light goes out??

Not sure but I will check that out next. I did pull the wire from the proportioning valve switch and the light went out. I guess that means the switch could be bad. Thanks

 

[pschlosser]

Not sure but I will check that out next. I did pull the wire from the proportioning valve switch and the light went out. I guess that means the switch could be bad. Thanks

Nice work. You're on the trail to solving it. So it looks like the wiring is fine, well done.

Is this a factory disc brake car? If it was converted from an all drum car, it's possible the proportioning valve (which is unique to the front disc, rear drum setup) is the problem. Either way, it looks like we know that switch is always on.

 

[sixpactogo]

Not sure but I will check that out next. I did pull the wire from the proportioning valve switch and the light went out. I guess that means the switch could be bad. Thanks

Pretty sure your problem is in the proportioning valve. They get gunky and sticky from years of use. I just rebuilt one like yours. If I were you, I would remove it and take it apart for cleaning. You may not need any new parts but the rubber seals and O rings are available if needed. There are a couple U tube videos on line showing how to do it. Just take your time and take lots of pictures so you know how to put it back together. What is happening with yours is the cylinder has moved to one side or the other allowing the plunger in your switch to send a ground to the light. You need to get that cylinder moved back to center to turn the light off. I have a few tips for you if you decide to repair it yourself.

 

[pschlosser]

Any chance the E brake is pressed, or issue with that switch?

Unlike newer generation cars, I don't believe the parking brake activates that lamp.

EDIT: Derp, I just tested it, and the warning lamp indeed comes on with the parking brake applied.

 

[sixpactogo]

Unlike newer generation cars, I don't believe the parking brake activates that lamp.

It does but he already made that test and proved it was his proportioning valve switch.

 

[kellydw]

Nice work. You're on the trail to solving it. So it looks like the wiring is fine, well done.

Is this a factory disc brake car? If it was converted from an all drum car, it's possible the proportioning valve (which is unique to the front disc, rear drum setup) is the problem. Either way, it looks like we know that switch is always on.

 

[kellydw]

Yeh it is a factory front disc brake car. The car sat for 16 years so you are probably right with the proportioning valve need cleaning. First problem I had was no fluid to the rear brakes and after trying several things turned out the wheel cylinders were plugged - cleaned the small holes for the bleeder and brake line and works fine now. I was putting cleaning the proportion valve off but guess I have no choice now lol. Thanks millions for the help - will let you know how it turns out.

 

[kellydw]

Pretty sure your problem is in the proportioning valve. They get gunky and sticky from years of use. I just rebuilt one like yours. If I were you, I would remove it and take it apart for cleaning. You may not need any new parts but the rubber seals and O rings are available if needed. There are a couple U tube videos on line showing how to do it. Just take your time and take lots of pictures so you know how to put it back together. What is happening with yours is the cylinder has moved to one side or the other allowing the plunger in your switch to send a ground to the light. You need to get that cylinder moved back to center to turn the light off. I have a few tips for you if you decide to repair it yourself.

 

[kellydw]

Yeh I am going to take it off tomorrow and clean it. There is a pretty good diagram in the Chrysler manual of the internal parts so it will help with the reassembly. Any hints would be greatly appreciated

 

[sixpactogo]

Yeh I am going to take it off tomorrow and clean it. There is a pretty good diagram in the Chrysler manual of the internal parts so it will help with the reassembly. Any hints would be greatly appreciated

Take your time dis assembling and take pictures so you know how it goes back together. Don't lose that little spring and brass hat at the bottom of the metering valve assembly like I did. Once you have that all out of the unit, you can use a 1/8" long punch to push the shuttle valve brass fittings out along with the seat for the rear brakes.
I used a brass 1/2" round brush that I chucked into my drill. I wrapped a 2" X 3" piece of red 3M scouring pad around the brass brush and polished up the bores. Here is some pics of the brush and 3M pad. If your O rings and rubber parts are ok just clean em up and re-use them. When you put the shuttle valve back in, make sure the groove is directly below the area where your switch goes in. If not you can move it with a small pick. If you want or need new O rings I also included a pic of the three kits needed to redo the rubber parts. Put it back together with some clean brake fluid and make sure your shuttle valve is centered properly or your light will be on again. Good Luck.

 

[kellydw]

Take your time dis assembling and take pictures so you know how it goes back together. Don't lose that little spring and brass hat at the bottom of the metering valve assembly like I did. Once you have that all out of the unit, you can use a 1/8" long punch to push the shuttle valve brass fittings out along with the seat for the rear brakes.
I used a brass 1/2" round brush that I chucked into my drill. I wrapped a 2" X 3" piece of red 3M scouring pad around the brass brush and polished up the bores. Here is some pics of the brush and 3M pad. If your O rings and rubber parts are ok just clean em up and re-use them. When you put the shuttle valve back in, make sure the groove is directly below the area where your switch goes in. If not you can move it with a small pick. If you want or need new O rings I also included a pic of the three kits needed to redo the rubber parts. Put it back together with some clean brake fluid and make sure your shuttle valve is centered properly or your light will be on again. Good Luck.

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[kellydw]

Geez thanks a lot for the info - even have the brush and scouring pads so I'm good to go. ***** of a spot to get at to remove it and all the lines but we'll manage. Thanks again

 

[sixpactogo]

Geez thanks a lot for the info - even have the brush and scouring pads so I'm good to go. ***** of a spot to get at to remove it and all the lines but we'll manage. Thanks again

If you can wait a day or so, spray all the line nuts with some PB blaster or some rust inhibitor and let it do its thing first.

 

[pschlosser]

@sixpactogo hey where did you get that brush? Is that a 22ga gun barrel brush, or a welding tool?

 

[sixpactogo]

@sixpactogo hey where did you get that brush? Is that a 22ga gun barrel brush, or a welding tool?

I got it at Harbor tools. I believe there were 4 brushes in a package. Two brass and two steel. Don't recall the cost but under 10 dollars. No idea on their application but they worked great for my use.

 

[moparleo]

Instead of putting off a potential brake failure, Brake fluid absorbs water.
The brake system will rust and degrade from the inside out. Your brakes are the most critical safety item oin yor car.
I would and have done this many times over the years.
Re place the brake system components from front to rear and then flush the brake fluid from the system every 2 years.
All of the brake system componnnets are available new and do not cost much.
New master cylinder, never rebuilt. Brake booster, all metal brake lines, do not use s/s. Front calipers, available rebuilt with all brake hardware. new front brake hoses, rear brake hose, new wheel cylinders. A perfecty time to also replace rear shoes with bonded lining, new hardware and self adjusters. Front bearing replace and seals.
Remember that the brake system is over 50 years old.
For a few hundred dollars you can have a car that brakes safely and quickly.
Buy quality parts for the brake system and have peace of mind.
Just cleaning the crud from a few inches of brake lines is just asking for problems.
Look at it like your brake system is you bodies circulatory system. You have a have a blockage in your arteries.
You can just try to clear the artery by pushing the blockage farther down your arteries and cause a heart attack or replace the artery and remove the blockage.
You don't want blood clots in your brake system.
Proper maintenance is key to a car giving you years of trouble free service.
Just like regular oil changes. You don't wait until the oil light comes on to change the oil, don't treat the brake or cooling system that way either.