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1970 Mustang brake light on dash


#1

Hi.
I changed my entire rear drum brakes on my 1970 mustang. After done I bled all 4 corners and the first time I pressed on the brake petal the brake light came up on the dash. The brakes are fine and do not have that spongy feeling and perform fine, but the brake light wont go out. What have I done wrong and how do I fix it.


#2

there is a switch that turns on the dash light in the brake line somewhere under the master cyl. Probably on the left front inner fender.

to re-set it bleed the brakes again. it is supposed to center its self then.

Years ago I had this same problem on a 1967 Fairlane, and the switch was gummed up and stuck witch could be the problem.

good luck


#3

Thanks jrb23321. I’ll take a look


#4

jrb2 is correct. Look on the inner fender apron next to your master cylinder. There will be a brass brake proportioning valve. On that you will see a plastic white or possibly greenish switch with a wire harness connector. That is the source of your dash “BRAKE” light. Inside the proportioning valve is a little plunger that shifts if there is an imbalance between the front and rear brake hydraulics, which then actuates the switch, lighting the dash light. You will need to rebleed the brakes, which should reposition the piston - but there may be some difficulty getting it to recenter. Follow the instructions in your 1970 Ford Service Manual if you run into problems recentering the proportioning valve.


#5

I know sure about the switch is on mustang ! But my on 1974 maverick is on the brake pedal.


#6

Thanks Mike_B
Yes it’s there. pulled the wire harness off the switch (mine is white) and the light went out. Did some online reading and everyone seems to be saying that these, proportioning valve are not servicable should the plunger/piston get hung up on the inside.
Brakes work and respond fine with no sponginess so I will have to bleed the brakes again when I put her to bed for the Winter.


#7

Hi Steve,
Depending on your abilities, the proportioning valves ARE servicable.
Check out this video from West Coast Classic Cougars, where they demonstrate the repair ('70 Mustang and Cougar use the same proportioning valve).

You can find the repair parts at Muscle Car Research. Here is a link to thier repair kit reference page;
https://www.musclecarresearch.com/valve-kit-crossref

Nice winter-time project :wink:

Good luck, Sir!

Mike B.


#8

When bleeding brakes with a proportioning valve like this, there is actually a center retaining tool that screws into the position that the brake light switch occupies. Be careful, when out of position, excessive pressure inside the proportioning valve can cause a loss of brake fluid past the piston and out through the brake light switch.


#9

Hi Mike.
Excellent video and great tips.
Thanks so much!!


#10

Hi speedyz68
Did not know that. Do you happen to know where you could get one of these tools. Is the tool to prevent the piston from moving too far in either direction or to prevent it from moving at all? If the piston is held secure, how can you bleed the lines or is it just done by gravity by opening the bleeder screw on each caliper?


#11

Muscle Car Research also sells the tool. But it looks pretty simple, and you could probably make one yourself.

https://www.musclecarresearch.com/brake-valve-tool


#12

It keeps the piston from moving at all. Fluid still flows through the block under pressure so you can bleed them normally. If you take the switch out, you should be able to re position the plunger with a small pick. It doesn’t move very far to turn the warning light on.


#13

Great idea.

Thanks and I will give it a try


#14

Hi All.
Does anyone know if the switch twists/unscrews or if it just pulls straight out? I don’t want to break it off.

Thanks
Steve


#15

It unscrews and has a hex head on it for a wrench. They are made of plastic, and most have a rubber o-ring on them.


#16

Excellent.
Thanks speedyz68