My '78 doesn't seem to have a parking gear. It takes the truck out of gear but rolls freely. It is a 4x4 460 truck so I am assuming it has the C6. The pointer needle on the column is off. It is directly in between the characters, to the left of the gear where it should be IIRC. Through search I have come up with the "prawl" in the tailshaft of the transmission and shift linkage adjustment. I am, of course, hoping I can just adjust the linkage. How is this performed? And as far as the prawl, I understand the TC must be dropped, but if it is shot can it be fixed without dropping the trans? Thanks!!

 

You can check to see if the problem is internal or linkage related.
Get under the truck and loosen the shift linkage at the transmission.
Once it is loose, push the shift arm up all the way. This will put the transmission in park. Try pushing the truck and see what happens. If the parking gear and all the internal linkage is okay, you should be able to move it a couple of feet at most before the parking gear locks. If you can push it further there is a problem internally and you will have to pull the pan and possibly the tailshaft housing. The actual parking gear is located in the tailshaft housing but the linkage that controls it goes into the gearcase, also, just a note, the parking pawl (not prawl) is the "hook" that grabs the parking gear to keep it from turning.
If it does lock okay manually then adjusting the linkage should take care of it. First check the hole in transmission shift arm for wear (these do wear, I've got two sitting on my workbench that were worn and causing the same problem you're describing). Then check the small stud that connects the shift arm to the shift rod for wear also. If both parts are okay then adust the linkage.
Here is the procedure from the Ford Service Manual:
1. With the engine stopped, place the transmission selector lever in the D position and hold against the D stop.
2. Loosen the shift rod adjusting nut. (this should be done already)
3. Shift the manual lever at the transmission into the D position, second detent from the back of the transmission. (pull the lever all the way down and move it back two "clicks")
4. With the transmission selector lever and the manual lever in the D position, tighten the nut to 12-18 ft/lbs torque. under no circumstances should the linkage be adjusted in any position other than the D position.
5. Operate the lever in all positions to make certain that the manual lever is in full detent in all gear ranges. Readjust linkage if required.
Below is a picture of the linkage. The arm with the long slot in the rod is the manual linkage. The other one with the black rod is the kickdown linkage and isn't associated with the park gear.

 

Thanks for the info!! The external linkage was not the problem unfortunately. What am I looking for when I drop the pan? Thanks again!

 

Here is the illustration from the Ford Parts book.
click on the .pdf file to open

 

Wow, that's an ENORMOUS help! Am I right in thinking the pawl is #7A441?

 

Right, the pawl is 7A441