1969 Ford Bronco with 1970s C4 Automatic Transmission Not Engaging Drive

[rwroclawski]

I have a 1969 Bronco with a 1970s C4 Automatic transmission that will no longer shift into Drive. If I give it some extra gas, it will sometimes kick into drive but it rumbles. If I shift in reverse, 1st, or 2nd I can get it going. After looking around and talking to some mechanics, I was told to look into the transmission vacuum modulator. The one that I found to be compatible and will be replacing with this week was the Pioneer Inc. Automatic Transaxle Modulator - 747011 (https://www.oreillyauto.com/detail/...utomotive-suv-1969-ford-bronco?q=747011&pos=0)

What should the vacuum pressure range be for the vacuum modulator at idle and as I give it some gas? Right now if I test the vacuum pressure by connecting directly to the carburetor and the end of the line that connects to the modulator I am getting a stable 15 Inch/Hg when idling.

Also, if anyone else has any ideas on what the overall problem could be. I would love to hear it.

Thank you in advance

 

[Broncobowsher]

I would have started with checking fluid level. And condition.
There is a chance the filter fell out of the valve body as well.
Modulator does not control if it will go into gear. It will control how hard it goes into gear/shifts and what speeds the transmission will shift.