1979 f150 has a completely rebuilt c6 transmission. The shifter says it's in park but when you turn key over, it's dead until you hold the shifter up. My mechanic kept adjusting nuetral safety switch until it worked. Now it's back like it was. Actually getting worse each day. Last night I moved the shifter almost an inch before it started. I think it's mechanical instead of electrical. Anybody else had this problem?

 

Check the linkage for wear. The stud that connects the shift linkage to the shift arm on the transmission is particularly prone to wear.
Also, the shift socket (AKA shift collar) could be starting to crack, causing extra play.
Here's a couple of pictures of a worn shift arm and stud.

 

OK I will check. Thanks. I'd say that's not included in transmission rebuild is it?

 

I'd say linkage, probably not. Shift socket, definitely not.

 

OK thanks, just when I thought I was ready to roll. I appreciate the info.

 

Thanks for pictures. I'll check

 

Mine has this issue, I think of it as theft deterrent

 

Lol, you sound like my mechanic. I just can't stand it.

 

one day I'll fix it, it's not a pressing issue compared to other things not working, like heat or turn signals

 

I think '79 shift collar is some different from my '77 .... but when I had same issue and it got worse, it got bad enough I became concerned that it was gonna leave me stranded ... so I R&R-ed it and saw how bad it was ..... cured it.

 

You're correct, the 78-79 shift collar looks different from the earlier versions but they still suffer from a weak internal bridge that likes to crack.
Here's a collar for the 78-79 trucks. You can see it still has the bridge across to the center.

 

OK .... I see .... could leave one stranded easy enough with the right break.

I fixed that tab on my column after you (I think it was you) sent me a link for Dennis Carpenter, but the bypass switch I wired in temp for the neutral safety switch I left in place so if the collar ever did let go, I could reach under the hood and get it in gear and start it.