Hi, I posted this in the transmission forum too, but since it is a problem that seems to have been caused by engine work, and I've been posting about this engine work all over this board, I figured the people reading here this may be able to offer more insight.
I recently finished a rebuild on the 400 engine of my 1979 F150 4X4. I put in a new big cam, strait up timing set, heavy springs, intake, and a new holley 4 barrel carb. My truck has an automatic transmition, that before this rebuild worked absolutely flawlessly.
I did the rebuild with the engine in the truck, so nothing related to the trans moved at all. After getting the engine all tuned in, and everything else working again, I took the truck out for a test drive, and found out very quickly that I had almost no ability to shift, and am stuck in one of my lowest gears.
The transmission is also knocking, off and on, and the gears grind occasionally, especially wehn I'm idling. And when I give it gas, it feels like I have a standard with a butter covered clutch. It almost doesn't accelerate, the engine revs against nothing, and the transmission knocks more. Going up hills almost doesn't work. Everything will very occasionaly catch, and then I feel how the truck should really feel, but it doesn't stay.
How could I have such a major transmition problem come up out of nowhere?
Thanks for any help, AleX

 

Don't mean to insult, but lets start obvious. Did you pull the torque converter off and loose fluid? Next would be if you pushed the converter in too far and wrecked the pump.

 

If I read the OP's post correctly, he didn't unbolt the engine from the tranny...

I may be off-track here but, how's the kickdown linkage?

 

It does sound like the tip of the converter went round.... it happened to me once, i thought it was the whole tranny. symptoms were exactly the same.... it could be that he converter was a bit old and the addon of power finished the job...

 

Right, I never moved the engine or tranny, or seperated them from eachother at all.
The kickdown rod is intact and attached to the new Holley 4 barrel. There is a screw on the kickdown rod linkage on the carb that is unscrewed all the way (set so that the kickdown is kicked in as soon as it can be set to do).
From the things that have been suggested here, the one about the torque converter (which I could use some explanation on in general) being old and failing seems like the most probable, but what do I do to fix that, seperate the engine and transmission and replace it? And is there any way to tell if that is the problem for sure?
Thanks, AleX

 

check the vaccum modulator, and make sure the hose is in good shape and conected to manifold vac source.