Stop Light switch

[DollyDodge]

Does anyone know where I can get a wrench that fits the stop light switch on the master cylinder?

Rob

[Reg Evans]

I just changed one using a medium sized crescent wrench but a 1" socket works too.

[Merle Coggins]

I use an 8" Cresent wrench, but any open end or 6 point wrench/socket the correct size would work. Unfortunetly I don't know which size off hand.

Merle

[DollyDodge]

Merel: This switch doesn't look like a regular nut like some of the brake swithes I have seen. This one is scolloped (for lack of a better description). It doesn't have a flat surface on it anywhere. A cresent or socket won't work. We have a 49 ton and a half dodge and it has the same shape. I can't figure out how to get it off with out damaging it (I am rebuilding the master cylinder). Maybe I should just leave it in place. I think it still works.

[austinsailor]

There is a special socket for those, but I haven't seen one in 30 years. I put mine in with a normal wrench. There is one size that will fit, although I don't recall what it is. I just tried them till One worked.

[Young Ed]

Is this it?

http://www.mytoolstore.com/kd/kdengi12.html

[pflaming]

The switch is activated by pressure, as I understand it. Oil or air? Also, if the brake oil is low the switch activates late, so that the brakes could be activating before the switch. Is that true.

I was told that later cars/trucks use a switch / micro type / activated by the brake pedal. Has anyone changed to the latter?

[Merle Coggins]

Is this it?

http://www.mytoolstore.com/kd/kdengi12.html

I actually have one of those sockets, but it's been so long since I've used it I almost forgot about it. Mine is from S-K #4488. As I said earlier, I've just used a Cresent wrench and have had good luck. I've changed a few recently as I've had a string of faulty ones from Napa. The latest one seems to be holding up so far. I think I'll toss my socket into my truck tool kit for the next time.

Merle

[TodFitch]

The switch is activated by pressure, as I understand it. Oil or air? Also, if the brake oil is low the switch activates late, so that the brakes could be activating before the switch. Is that true.

I was told that later cars/trucks use a switch / micro type / activated by the brake pedal. Has anyone changed to the latter?

Neither oil nor air: It is the pressure of the brake fluid that activates the switch. Brake fluid is not an oil... The switch sees the same pressure as your wheel cylinders, so having "brake oil" low should affect the stopping effectiveness the same as the switch. Once the fluid is low enough to draw air in to the system you have stopping issues.

Not sure what all vehicles use nowadays but I think at least some motorcycles use a hydraulic pressure switch.

[Young Ed]

I actually have one of those sockets, but it's been so long since I've used it I almost forgot about it. Mine is from S-K #4488. As I said earlier, I've just used a Cresent wrench and have had good luck. I've changed a few recently as I've had a string of faulty ones from Napa. The latest one seems to be holding up so far. I think I'll toss my socket into my truck tool kit for the next time.

Merle

I bought one from napa to change the oil pressure sending unit in a friends Dakota. Tool was mine to keep for working on their truck. Of course I haven't used it since.

[DollyDodge]

Thanks again for the info. I didn't think a cresent would work on it but I will try it and also will see if one of my sockets fit. I wouldn't mind buying one of the specialty sockets too, just to have in the tool box for fun.

Rob

[DollyDodge]

Over the weekend I had a look at the stoplight switch and sure enough a cresent or regular wrench works to take it off. Just looking at it I would have never guessed a regular wrench or socket would work. Should have looked closer I guess. Anyway the old switch is off and new one is on the way from Rock Auto.

[greg g]

You probably should have left the old one it till the new one came, you might get some air and moisture in the system. I would scre the old one back one in if you havn't already.

[Jerry Roberts]

You probably should have left the old one it till the new one came, you might get some air and moisture in the system. I would scre the old one back one in if you havn't already.

You might also accidentaly step on the brake .

[oldmopar]

There is also the mechanical version.

Mechanical switch

[DollyDodge]

I should have clarified. I have the master cylinder out of the truck. I also am rebuilding each of the wheel cylinders. A couple of the pistons in the wheel cylinders were stuck, and the cups were hard as rocks. The old truck sat for 30 years since we last drove it. I tried to just fill the master cylinder and bleed the system, but there were leaks in multiple places. Anyway, I have a master cylinder kit and that is the next project, to redo the Master cylinder. I got the front cylinders done last weekend and reinstalled them, new brake hoses, new front seals, and repacked the bearings (bearings were in good shape). Now it is on the the rear brake cylinders.