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th400 swap crossmember ?

G

GRAYTEXK5

1/2 ton status
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Jul 23, 2002
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Ft. Worth, TX
ok, I just got the th400 in my blazer, but what do I do about the crossmember? is there a different crossmember for a t400 in a K5? the 400 is about 2.5 inches longer than the 350, and I thought I could just drill new holes in the frame. well, I can do that for the hole towards the front...but the rear one ends up right where the frame starts to widen, so if I was to drill a hole there, it would put it right on the inside edge of the frame. what have you other guys done when doing this swap? do I need to just drill another hole, closer to the front one, through the crossmember? is there something really simple I'm missing here? this is all I lack to getting this swap done, so...I'd appreciate any help you can give me. thanks /forums/images/graemlins/1zhelp.gif
 
The crossmember is the same crossmember and should work, TH400's were found in K5's.
I don't know what to tell you, other than it should be working perfectly fine.

If it is the 79 in your profile, it WILL work, it is the same frame as my '78 and I've even pushed the driveline back a couple inches.
 
yes, it is a '79...what t-case does yours have? would that make any difference? mine is a 203, I don't know if it would be a different crossmember with a 205 or not? I can probably rig this one up to work somehow, but...I just wanted to find out if there is a different crossmember I could get or something, before I started drilling a bunch of new holes.
 
When were TH400's ever put into K5's? My understanding is the 1/2 ton rigs always got TH350's (or later, the 700.)

-- A
 
did you have to drill holes in the crossmember, or just the frame? because if I just drill through the frame,right where the holes are on the crossmember...the rear ones will be right on inside edge, actually leaving one side of the hole open. I don't think that would hold, would it?
 
I just drilled the frame, But I didn't hve the same problem you seem to have. both my holes are in the middle of the rails. I have a stock style 205 crossmember.
 
[ QUOTE ]
The crossmember is the same crossmember and should work, TH400's were found in K5's.

[/ QUOTE ]

What year K5 would have a TH 400 in it? Diesels?

The crossmember should certainly work, reguardless.
 
[ QUOTE ]
When were TH400's ever put into K5's? My understanding is the 1/2 ton rigs always got TH350's (or later, the 700.)

[/ QUOTE ]

1/2 ton pickups with big blocks in the '70s had TH 400s from the factory, but that is the only instance I've ever heard of a 1/2 ton with a TH 400 unless 82-91 6.2 L Diesel K5s or 1/2 tons came with TH 400s, but I highly doubt that (all the ones I've seen were 700R4s).

I have never seen a K5 with a factory TH 400. If one exists, I'd like to know what configuration.

1/2 ton trucks, yes, but definitely rare. Only 454 powered 1/2 tons as far as I know.
 
ok, well I don't know why mine seems to be different from everyone else's...are some 400's longer than others? anyway...thanks for the help guys. I'll get it mounted one way or another.
 
The th400 was an option in the k5 from 75' till 80" look here
CK5 has all the info. /forums/images/graemlins/deal.gif/forums/images/graemlins/thumb.gif
 
Ahh. Must have been the 400 small blocks that caused that choice. /forums/images/graemlins/thumb.gif
 
Hmm. I wonder where Steve got his info from; the "generally accepted" story that I know of -- and from Chuck's page is that TH350's came in 1/2 tons and TH400 in 3/4 and 1 ton, period.

Mind you, I can't prove it, which is why I'm posting here /forums/images/graemlins/smile.gif

I also wasn't aware that big blocks ever came in 1/2tons -- remember the 400ci in the 73-79 years was a small block, not a BBC.

My Chalet, f'rinstance, has what I believe to be the original 400ci small block, backed by a TH350.

Speaking of options, Chuck's page lists the RPO's for the two trannies as M40 for the TH400 and M49 for the TH350... whereas my '74 K5 has RPO 1M40 with a TH350.

GM may have changed the RPO code from year-to-year, or the codes for the pickups may be different than the ones for the Blazers (and maybe Burbs?)

To summarize: GM did all kinds of weird crap. If anybody has a build sheet for a K5 with 1M40, I'd love t know which tranny you think it came with.

-- A
 
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