Tranny differences? Pre'74 vs post '74

[jode]

I am trying to work a deal out with some friends where we do some tranny swaps and whatnot....I have a line on a post-74 parts wag with a TH 400/QT for $50. I intend to get it either way, but I have a freind who is interested in the tranny for his pre-74 J3000. He says that the tranny bellhousing pattern changed around '74 and that the only TH400s that will fit his truck are the pre 74s. Is this true? Is there any way to get around it, or is he going to have to find a different tranny? :confused:
Thanks

[joe]

I'm not 100% on the year but 74 sounds correct for when the trans cases(TH400) used an AMC specific case (AMC bolt pattern). Prior to that they used a case with the Buick "nailhead" bolt pattern w/an adapter. My 73 TH400 was the nailhead pattern w/adapter.

[jeepguzzi]

You can swap out the guts to his case. Inside (except for the tailshaft) is all the same, no matter where it came from!

[jode]

BUMMER :(
His case is what has the problem...it is cracked....the case is what he needed...and I needed to get him the tranny so that I could convince him to let me keep it in his yard while I part it out redface.gif
Now what cards can I pull to get him to want to work with me on this :confused:

So he was right...he does need an early TH400 (nailhead) and there are no commonly available adaptors?

[Alaskaman]

Actually the engine bolt pattern is same on all AMC engines found in the Jeeps, so the nailhead TH400 with AMC adapter will bolt up. That said, there are some differences in floor pan clearance in the adapter area that a BFH will fix, and the flex plates are different before/after the changover in 74. Starters are same, not sure but overall case length as installed may be slightly different between the two, which would affect driveshaft length. A tape measure will tell quickly enough.

So, if you want too bad enough you can fit a pre 74 TH400 with adaptor into a 74 up rig, or vice versa but be prepared for some little surprises. Probably easier to swap guts, if that's an option...A half sixpack job once everything is clean and tools are at hand. Get a VHS tape on TH400 rebuilding if you are new to it, its a piece of cake once you know how.

[jode]

Well, that is a horse of a different color!
So what you are saying is that he jsut needs to use the adaptor that he already has (on his old cracked TH400) and bolt it onto the new TH400 case?

How hard is that adaptor to get on and off?

Did I understand correctly?
Anybody confirm this?
Thanks

[Alaskaman]

Nope, the adapter in question mates a nailhead TH400 to any 70's and up AMC engine. Thats in 71-73 rigs. In 74, a new TH400 case was introduced that fits the same AMC engines, but without needing a separate adaptor. The internal workings will interchange.
Clear as mud?

[RustyJeep]

Pretty much, swap that TH400 in there!

[jode]

Clear as mud and I am stoked...this means that the whole deal can go through and I can pick up that whole wag for a song (cause my bud will be paying for most of it to get the tranny)

everybody needs a friend like me!
smile.gif