1978 Chevy K20 Crossmember Alignment

Picked up a 1978 Chevy K20 a few backs back and just got back from a 300 mile weekend driving it and noticed the crossmember bar bolts had come undone on one side. Previous owner put a 5.3 LS with a TH400 trans in. Jacked it back up into place to replace the bolts and it doesn’t line up with the holes in the frame. Is there a trick to aligning the crossmember or was something possibly bent before I noticed the bolts were gone? Also is this even the right crossmember?

Sometimes the frame rails can spread apart so you probably need to pull it inward some (ratchet strap, etc).

chrismcmorrow said:

Picked up a 1978 Chevy K20 a few backs back and just got back from a 300 mile weekend driving it and noticed the crossmember bar bolts had come undone on one side. Previous owner put a 5.3 LS with a TH400 trans in. Jacked it back up into place to replace the bolts and it doesn’t line up with the holes in the frame. Is there a trick to aligning the crossmember or was something possibly bent before I noticed the bolts were gone? Also is this even the right crossmember?

Click to expand...

I went through this as well when I did my swap, although I don't think the swap had anything to do with it because I had a 700R4 and the swap had a 4l60E.

Anyway, finally during the swap I learned to put the weight of the transmission on it to make it flex down bringing the holes together. Get a few threads on both bolts on one side started, then move to the otherside. May need to play with a single jack stand and hydraulic jack on the outside to get her to flex. She'll fit, but may take some finesse.

I've done it twice, but for the life of me I can't remember exactly how I did it. But once you see it, you'll be like d@nm that wasnt as bad as I thought.

remembered a bit more, I do remember going back and forth, side to side a few times to get the bolts in.

Yeah it’s not so much side to side as it is front the back. If you look at the second photo you can see the front hole it looks like it should go into. Looks about an inch back from there.

Looking at your pics closer, you have a mix of parts that don’t go together.

Your trans/tcase adapter appears to be a short foot design that is ‘85+ which should have a “W” shaped crossmember but the flat crossmember is for a pre ‘85 tall style adapter. Those parts were never used together, it makes me wonder if the engine/trans/tcase assembly is tilted down too much towards the rear.

nvrenuf said:

Looking at your pics closer, you have a mix of parts that don’t go together.

Your trans/tcase adapter appears to be a short foot design that is ‘85+ which should have a “W” shaped crossmember but the flat crossmember is for a pre ‘85 tall style adapter. Those parts were never used together, it makes me wonder if the engine/trans/tcase assembly is tilted down too much towards the rear.

Click to expand...

Yep, that's what I'm seeing too.