Hey guys. I started this thread not looking for answers, but to hopefully provide some. I'm sure this could have been discussed in the past, so that is why I titled the thread with as many searchable words related to the problem I could.

I got in my 1973 F100 yesterday (360 - C6 auto) and set out down the road with the transmission in "D". Much to my surprise, the truck would not shift out of 1st gear. I dropped the lever down to 2 (2nd) and the truck shifted into 2nd gear immediately. I then shifted back into "D". The truck remained in 2nd and would not shift into 3rd.

All of this was accompanied with a rather rough idle. I managed to get it home just fine, popped the hood, removed the air cleaner and found my problem. The vacuum line running from the vacuum modulator down on the transmission had slipped off the vacuum tree nipple located just behind the carburetor. I slid it back on and secured it with a stainless steel hose clamp.

The truck fired right up, idled smooth and shifted perfectly after.

Hopefully, this thread might help someone in the future.

 

Ross, a belated welcome to FTE.
I have a '73 F100 Explorer myself. Right now it's going through a somewhat drawn out restoration but it will get done eventually.
Thanks for posting that, I'm sure it will help someone down the road.

 

Excellent find!

FWIW,

One other item to check in regards to the vac. hose is the presents of ATF.
If there is ATF present in the line, it is a indication that the diaphragm in the the trans modulator has ruptured and should be replaced.

 

Good info. Thanks.