Brake lights staying on

-

crewchief

A & P Mechanic
FABO Gold Member
Joined
Jan 17, 2014
Messages
656
Reaction score
364
Location
Malta NY
Just replaced the M/C and rebuilt booster (from Booster Dewey) and now brake light remain on until I pull the pedal back. The pushrod was set with .0020 clearance.
Not sure why the pedal won't return normally, any thoughts?
 
I had that after a MC replacement as well. I adjusted the switch and added a spring to the pedal.
 
Just replaced the M/C and rebuilt booster (from Booster Dewey) and now brake light remain on until I pull the pedal back. The pushrod was set with .0020 clearance.
Not sure why the pedal won't return normally, any thoughts?

Did you use an OEM replacement master cylinder?
 
I had that after a MC replacement as well. I adjusted the switch and added a spring to the pedal

There is no need for a return spring just adjust the brake light switch.

There is a bolt and slot in line with the black rubber coated wire retailer in the photo. It is accessable from the passenger side of the steering column

Screenshot_20200914-083510.png
 
The switch has been a factory set for 48 years, if I pull the pedal back they go off. Always worked fine prior to M/C & booster replacement.
 
The switch has been a factory set for 48 years, if I pull the pedal back they go off. Always worked fine prior to M/C & booster replacement.
Same thing I had. If I remember there wasn't enough switch adjustment. When you replace the master with a new or rebuilt unit exactly the same as the one you took out and the pedal won't return it is frustrating. I should have rebuilt my original master. :BangHead::BangHead:
 
Hole in MC for the pushrod is a 1/16" more rearword?

The switch would have been set for the MC that was installed. You put a new one in.

The reason I know this is my dad replaced the MC in my dart and had the exact same problem.

His solution was to install a return spring. After he passed and I inherited his Dart. I did not know that he had had that problem but I found a funky spring hooked to the brake pedal. Not knowing why it was there I removed it. Next day the brake lights were on.

I climbed under the dash and adjusted the switch, no more problem.

He had had the MC replaced, a day or so before he found the brake light on and added the spring.
 
Same thing I had. If I remember there wasn't enough switch adjustment. When you replace the master with a new or rebuilt unit exactly the same as the one you took out and the pedal won't return it is frustrating. I should have rebuilt my original master. :BangHead::BangHead:
Thinking of doing that same thing, the old M/C was leaking into the booster, that's the reason for replacement. New parts from suppliers are always a crap shoot.
 
Just replaced the M/C and rebuilt booster (from Booster Dewey) and now brake light remain on until I pull the pedal back. The pushrod was set with .0020 clearance.
Not sure why the pedal won't return normally, any thoughts?

These things are not aircraft, and we are all dealing with Chineseoationized parts. There could easily be a small difference in the mc piston depth and it would not take much. The days of Raybestos, Wagner, Bendix "old school" parts manufacturers are long past.
 
I updated my 66 master cylinder from a single pot to a dual. I ended up buying an adjustable pushrod from Dr. Diff. That, and adjusting the switch did the trick.
 
That 48 year old switch has been cycled how many times in it's life? There is a reason its adjustable and replaceable. You adjust these thing to work properly or replace them with a new one.

My car does it too. After replacing the MC twice and digging around under the dash I'm sure its got bumped, moved, or just doesn't work right anymore.
 
The push rod has been adjusted to .0020 clearance.

If the piston is slightly different than the old one, that does not mean ****. Also bear in mind you have to have FOR SURE adequate movement in insure the piston returns past the compensating ports in the master
 
If the piston is slightly different than the old one, that does not mean ****. Also bear in mind you have to have FOR SURE adequate movement in insure the piston returns past the compensating ports in the master
Understood, I'm thinking it must be in the M/C for some reason it's not returning completely. That's why I have to pull back on the pedal for the lights to go out.
 
Just noticed the the teardrop end of the pushrod was up. I think it should be facing downward. Correct?
 
As an aircraft mechanic I couldn't let my self adjust anything or add something that was never installed by the factory.
I had to look at everything several times to figure out what had changed to cause the lights to stay on.

BINGO! I remember seeing the rod facing downward. The teardrop rod was the issue! Now the lights go off as they did before, no adjustments needed.

Thanks to everyone. Jack
 
As an aircraft mechanic I couldn't let my self adjust anything or add something that was never installed by the factory.
I had to look at everything several times to figure out what had changed to cause the lights to stay on.

BINGO! I remember seeing the rod facing downward. The teardrop rod was the issue! Now the lights go off as they did before, no adjustments needed.

Thanks to everyone. Jack
Teardrop rod? I would like to see a photo of that so I know what to look for.
 
-
Back
Top