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My master cylinder started leaking from the sensor that is on the front side on the top. Not sure what it is called and I can't find anything that is close to it online. Took a picture of it just in case, the sensor is in the circle. Any help is appreciated. Thanks.
Yours has a blue tag so it appears to have had the recall performed already. Before they added an inline fuse those switches would burn the truck down when they leaked. They are about $100 or more for a Motorcraft replacement.
Even though you have the fused recall harness I would disconnect that Brake Pressure Switch (BPS) as added insurance to not start a fire. The Motorcraft part referenced above includes a new fused harness and the redesigned BPS.
When they first came out in around 1992 they were called BOO switches IIRR
Most of those BOO switches last forever
Mine on my 1994 van is original and I have had both recalls done
I'd simply go to the junkyard and grab a good one for 5 bucks
You might even get lucky and find one of the newer designed ones that are not supposed to short out
Screw Ford and their 115 bucks for the updated part
1992 F-Series/Broncos still had the older vacuum servo speed control system. There was no Brake Pressure Switch (BPS). 1993 was the first year for the electronic servo setup. Both systems use the Stop Lamp Switch/Brake On-Off (BOO) switch as the primary trigger to deactivate the speed control system. The vacuum servo also used a vacuum dump valve activated by the brake pedal arm to dump the vacuum in the servo to atmosphere. The electronic servo used the BPS as a backup/redundant circuit to deactivate the speed control servo.
Basic 1993 and up electronic servo speed control diagram (without the recall harness):
Can anyone comment on replacing this? Is it simply screw out/screw new in, or do I need to bleed the system, too?
Also, what exactly is the function of this sensor/switch? If cruise is not used, can it be replaced with a plug to prevent further leaking?
Anytime you open the brake hydraulic system, the potential for air to enter is there.
It's not hard to swap the switch. Before you seat the switch fully, have someone press on the brake pedal slowly. As the fluid is coming out, screw it on tight. Top up the fluid, but remember, you don't want to top it up all the way, unless the brake pads and shoes are new.
Fluid will come out that hole when you unscrew the boo switch
Simply screw another in there is all I've ever had to do
Bleed the master cylinder if you want, but it's not necessary IMO
You are one who bleeds all 4 brakes after a master cylinder replacement too, right? 1Butcher?
Also, not necessary, sometimes did it anyway for feel good purposes
You are one who bleeds all 4 brakes after a master cylinder replacement too, right? 1Butcher?
Also, not necessary, sometimes did it anyway for feel good purposes
If I replace the master cylinder, do I bleed the air out of the master cylinder? Yes, 100% or the time. Does all the air go out the wheels? No, but I will bleed it there if the fluid is old. There are many different ways to bleed out the air of a master cylinder. You don't have to bleed it out at the end of the hydraulic circuit. The air must be out of the hydraulic system. How you get it out does not matter, as long as it is out.
I am in agreement with you in that you don't need to bleed the entire system when you replace a sensor/switch like this, but when it comes to making a recommendation to the public I tend to recommend the right way. @manicmechanic007 is one of the wise ones here and your words mean a lot. There are some people here that probably should not be touching their brakes or any other part of the car. That is why, as simple as it is to have a second person step on the brake pedal while making the last turn of the switch is not really a bad idea.
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