Speed-O-Driven

[Chasbod]

I'm looking at an original Factory Order for a 71 F 100 302 and it has an item listed as Speed-O-Driven and in the box is an "8". Looking under the hood, there is a servo type device at the firewall that connects the speedometer cables and has 2 wire leads leaving it. It doesn't look like any type of cruise control but rather a signal generating device for the speedometer cable.

Any ideas?

[68F250]

It's one of the components for the emission control. It goes along with the temperature sensor in the door pillar. Only used on F100's starting in '70. The system went by different names depending on the year but basically it allows the vacuum advance to work only when traveling faster than 28 mph. If the outside temperature dips below 65* then it allows the vacuum advance to work all the time. Glorified NOx device.

I was gonna get you a scan of that system, sorry about that. My house is upsidedown with home improvements and most of my reference materials are temporarily boxed away.

[Chasbod]

Thanks for the information!

[rjewkes]

mine only has the plug coming out the firewall. How bad is this? or is mine not required to have it because of the dual vacuum advance? and what is that two wire set that just loops back into itself? on the left fender?

[FORDification]

...and what is that two wire set that just loops back into itself? on the left fender?

That's the neutral safety bypass for manual transmission trucks. If your truck had a manual tranny, the jumper wire would be removed and a mini-harness plugged in there that would extend down to the transmission-mounted neutral safety switch.

[68F250]

Nothing to worry about, the engine performs better with it disconnected.

The wire loop is the jumper for the neutral safety switch that would have been used for the 3 on the tree outside the cab. With an automatic column, the neutral safety switch is on the column inside the cab.

[68F250]

I guess I type to slow...

[rjewkes]

And again i have learned something. Thanks guys.

[68F250]

Actually it's the backup light switch, but you get the point.

[FORDification]

Details, details!