Door Jamb "thing"

[Whoaaanelly]

Hey All,

I was at the local Pull a Part today looking for parts and scored some brackets for door jamb switches from a '72. These I understand, but in the door jamb is also some other "thing" with wires going to it, but I couldn't figure out by looking at it what it was. I haven't looked to see if my 67 has one yet. What is it?

[FORDification]

You're probably seeing a small round silvery disc? It's part of the emission controls on '70-'72 F100s.

[cdeal28078]

I have seen that on 2 72 models but can't remember the name or function. I think it has something to to with air temp. and timing right?
clint

[rjewkes]

Transmission spark control. It senses air temperature and a vaccuum switch under the hood mounted on or near the right hand(pass) Valve cover at the back switches the vaccuum on and off as required by the sensor input.

from what i've heard Spark control was junk especialy when talking about Milage.

[Whoaaanelly]

Keith -- That'd be the one. Would have never guessed it had anything to do with emissions control. Thanks for the info.

[TheEskimo]

Wow, I never knew what that was. Learn something new every day. Never thought to ask either.
Soon I will be a very egimucated and lernded inimividule.

[layedout72]

so ur saying a metal disc in the door regulates vaccuum in the motor? how does this work. I dont know if i have it or not, guess i will look tonite.

[Chasbod]

Barry (68F250) provided this explanation a while back to me:

"3. Here's another system that really should be disconnected. Basically it prevents vacuum advance from occurring unless the vehicle is going faster than 28 mph OR the outside temperature is below 65*. It's a glorified NOx smog device and reduces emissions at the expense of mileage and drivability. It also can cause overheating which is why you also have the system described in issue #2. I would not try to reconnect any of it. The best way to route your vacuum is one hose only, from the carb. ported vacuum to the outside nipple of the vacuum advance."

The other half of this system is a speedometer cable servo which provides the speed to the black control box mounted under the dash. The box sensed temperature from the disc and speed and made the decision to regulate vacuum advance.

There was also a separate vacuum control system which worked off a 3 ported temp switch mounted in the thermostat housing neck. If temp got too high, it turned on manifold vacuum to the vacuum advance and raised rpms. If you had this system, you had a dual port vacuum advance.

[68F250]

Thanks Chasbod, while you posted I was looking for some scans:

http://www.fordification.com/forum/down ... er=user_id

http://www.fordification.com/forum/down ... er=user_id