Topic: Brake Warning Light

[Stangly]

I'm having troubles getting the brake warning light to go off.  The car has drum brakes so I believe there is no proportioning valve.  I found something in the Ford service manuals that shows how to center the valve.  Is this process also used on the drum brake cars, or is this possibly a bad warning switch.

Thanks,

[krelboyne]

It is possible for the switch to fail.

My guess is that the piston is not centered, meaning the switch plunger is not in the groove.

[67gtasanjose]

I'm having troubles getting the brake warning light to go off.  The car has drum brakes so I believe there is no proportioning valve.  I found something in the Ford service manuals that shows how to center the valve.  Is this process also used on the drum brake cars, or is this possibly a bad warning switch.

Thanks,

Drum or Disc, both have a proportioning valve, no doubt it is stuck one direction or the other.

[preaction]

When the valve is in a position to trigger the warning light does the valve being out of place affect the braking ability of the car ?

[jwc66k]

Drum or Disc, both have a proportioning valve, no doubt it is stuck one direction or the other.

No, both have a distribution block with a brake failure warning light system. A proportioning valve is used only on disc brakes for early Mustangs.

When the valve is in a position to trigger the warning light does the valve being out of place affect the braking ability of the car ?

Not always. There's a technique to centering the "switch", different years have different methods. Haven't had to do one since 1970. Ask the new kids how.
Jim

[67gtasanjose]

No, both have a distribution block with a brake failure warning light system. A proportioning valve is used only on disc brakes for early Mustangs.Not always. There's a technique to centering the "switch", different years have different methods. Haven't had to do one since 1970. Ask the new kids how.
Jim

My-bad, You are correct. I used incorrect terminology, the common name across MOST CARS (NOT early Mustang specific) often called a proportioning valve. I forgot who we are dealing with here!  

[Mike_B_SVT]

I'm having troubles getting the brake warning light to go off.  The car has drum brakes so I believe there is no proportioning valve.  I found something in the Ford service manuals that shows how to center the valve.  Is this process also used on the drum brake cars, or is this possibly a bad warning switch.

Thanks,

You can disable the BRAKE warning light by disconnecting the cable connector from the switch at the brake proportioning valve.

The switch itself is "normally open".  When the piston in the proportioning valve shifts it causes the switch to close, shorting that warning circuit to ground, which lights the BRAKE warning light on the dash.  Disconnecting the wire connector from the switch prevents the switch from grounding that circuit, disabling the warning light.

You might try removing the switch and testing it, then clean it or replace it if necessary. 
When testing it, some things to remember: the two connector pins are a single metal piece. So they will always read zero ohms between them!
When you push in the metal switch plunger it come into contact with a portion of the pin piece. This shorts the two pins to ground through the plunger and brake distribution block, lighting the "Brake Warning" light in the dash. 
So to test it, measure the resistance from each connector pin one at a time to the end of the metal plunger on the switch.  It should be open / infinite resistance (if not, consider cleaning or replacing the switch).  Then when you push the plunger in the resistance should drop to zero.

If the switch plunger is stuck or sticky, it can sometimes be made to function again by squirting WD-40 or other solvent / lubricant up into the plunger recess.  Then you can possibly work a stuck spring loose.


Next step should be to attempt to recenter the proportioning valve. 

If that doesn't work, or you find brake fluid leaking from your switch at the proportioning block, it needs to be repaired or replaced.

Repair video:


Here is how I found mine when I bought my car ~ switch itself was missing and capped (due to leakage), and the connector was dangling disconnected.

[jwc66k]

My-bad, You are correct. I used incorrect terminology, the common name across MOST CARS (NOT early Mustang specific) often called a proportioning valve. I forgot who we are dealing with here!  

I got into a heated discussion with a wheel and brake shop worker, a young guy, about that subject. Newer cars have a combined distribution block/proportioning valve that includes the switch, and as far as he was concerned, they were always combined. After a calming was achieved, I asked him if he ever saw a car with front drum brakes. He was sure that those were used back in the 30's and 40's, and front disc brake were standard in 1950. Well now he knows different.
Jim

[midlife]

I got into a heated discussion with a wheel and brake shop worker, a young guy, about that subject. Newer cars have a combined distribution block/proportioning valve that includes the switch, and as far as he was concerned, they were always combined. After a calming was achieved, I asked him if he ever saw a car with front drum brakes. He was sure that those were used back in the 30's and 40's, and front disc brake were standard in 1950. Well now he knows different.
Jim

The young guy has to be correct!  Hell, bias-ply tires went out of style in the 20's.  C'mon, Jim, get with the program!

[bgp429]

Even when these cars were relatively new centering the switch could be tricky. It is sometimes not known what side the valve has slid to. What I did was open a bleeder and with my hand slowly pushed down on the brake. If the light flickered [went off and back on] it had slid to the opposite side, so open a bleeder on the other end and try it again. If the light went off quit pushing the brake, your done. Sometimes the valve would stick. Then stomping rather fast with a foot and open bleeder would free it up. Can't ever remember having to rebuild or take one apart to center the valve, however the cars were much newer and it may be necessary today.

[jwc66k]

The young guy has to be correct!  Hell, bias-ply tires went out of style in the 20's.  C'mon, Jim, get with the program!

I refuse to use the new-fangled rubber monstrosities on any horseless carriage I have, so there!
Jim

[tobkob]

Even when these cars were relatively new centering the switch could be tricky. It is sometimes not known what side the valve has slid to. What I did was open a bleeder and with my hand slowly pushed down on the brake. If the light flickered [went off and back on] it had slid to the opposite side, so open a bleeder on the other end and try it again. If the light went off quit pushing the brake, your done. Sometimes the valve would stick. Then stomping rather fast with a foot and open bleeder would free it up. Can't ever remember having to rebuild or take one apart to center the valve, however the cars were much newer and it may be necessary today.

+1   That is how we did it at the dealership I worked at in the early 70's.Was pretty easy with a helper 45 years ago but maybe "piston" could be stuck after all these years.

TOB

[krelboyne]

Scott Hollenbeck at Muscle Car Research (also associated with 428cobrajet.org.) Has a tool for holding the piston in the brake distribution block.

Pressure Differential Switch Lock Tool
https://www.musclecarresearch.com/node/283

[Stangly]

Guys,

Thanks so much for the help this information gives me some good places to start checking, there is so much to learn yet.

David,

[Bob Gaines]

Scott Hollenbeck at Muscle Car Research (also associated with 428cobrajet.org.) Has a tool for holding the piston in the brake distribution block.

Pressure Differential Switch Lock Tool
https://www.musclecarresearch.com/node/283

I think i got the centering tool  from NPD a couple years back.