1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Hi everyone, I have a 72 K20 that I am trying to get running. I have a rebuilt 350 motor,rebuilt turbo 400 trans and a rebuilt 203 transfercase. I am running into the problem of getting the transmission mounted on the stock crossmember. I believe I need a new cross member any ideas?

Thanks for the help.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

why 203 t-case. the 72 should be a 205. picture of what you have?

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Welcome to the site Al. You're running into issues because the combo you're attempting to install never came in a 72 K20 from the factory. A 72 K20 with auto trans would have come with a TH350/NP205 combo. Your TH400/NP203 combo is a squarebody era drivetrain. So you may indeed need a custom crossmember to mount your combo - and I don't know the effect of the TH400/203 combo on mount location in a 72 etc. Was the truck apart when you bought it? I realize I haven't answered your question, but at least now you know why it doesn't fit :). While the TH400 is a popular upgrade to a pre-squarebody 4x4, the challenge normally lies in mating it to the NP205 - an adapter is needed. TH400/203 combo retrofit is not common because the 203 is notably weaker than an original 205 (chain vs gear driven). 203 into a pre-square is usually only done out of necessity - i.e. it came with the truck or someone had it lying around the garage when their 205 grenaded (which is hard to do...) Hopefully someone here has swapped a whole squarebody driveline into this era and can provide some more useful info for you. In the meantime, it might not be a bad idea to keep your eyes peeled for an NP205 t-case that someone is wanting to sell.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

I would think a cross member from a truck that came with a NP203 would work.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Thanks for the replies, bought the truck as a roller the drivetrain came out of an 87 I had sitting around with a 73 body on it. I got rid of the tbi heads, intake and put on a set of vortec heads along with a carburetor set up.

So for me it made sense to just use the stuff I already had sitting around.

I know I will most likely have the drive line probably shortened or extended. But as of right now I'm just trying to get this all figured out.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Which body was originally on the 1987?

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

K20.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Your ‘87 would have had a 208 t-case as well and not a 203 full time case.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Sounds like you have the '73 transfer case. The crossmember has nothing to do with the transmission. That floats between the engine and transfer case adapter. It's the transfer case adapter that has a crossmember. What is the problem you are having exactly? Floor clearance, front to back alignment with crossmember? You can move the crossmember. How about some pictures? Is the truck an original K/20 and the crossmember the original... so would be for the NP205?

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Thanks for your reply’s, I have installed the drivetrain and had a new driveshaft made to fit. I confirmed I have the NP208 and have a crossmember for that setup.

The issue I am now running into is the top of the transfer case is hitting the cab preventing me from bolting the crossmember to the frame. As the transfer case rest against the cab I have an approximate 1.5 inch space between the frame and the crossmember. Does anyone have any ideas? Maybe a shorter mount?

Thanks for all the help.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

The floor on a mid 80’s sometimes has a raise portion clear back under the seat to clear the np208. Not just a bolt in high hump. You may have to massage your cab floor.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

About a 1" body lift is needed when mounting a 67-72 body on a '73-'87 chassis. The frame rises up that much more in the area under the bed. The cab lift is required even just to have the body line up properly. GM used all room available with that extra space under the cab and the crossmember reflects that.

Your core support is moved back a couple few inches, too, with the ends of the frame cut off, correct? The newer frame is longer from cab forward. You engine should be less tucked into the firewall as well

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

The Body lift was my other thought. The cab and frame are stock and it does have a 6 inch lift on it. I’ll try to get some photos downloaded today.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

I was thinking he was using a 67-72 frame.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

I am using a 72 frame and body. The drivetrain is out of an 87 that I had. It’s all rebuilt and ready to go.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Ok. I got lost in it between the old posts and new, '73 this, '87 that, 203, 208, '87 drivetrain, '73 body...

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Ok I’ll start over. It’s a 1972 Chevrolet K20 ac cab. The previous owner put a 6 inch lift on it with 35s. I’m not the biggest fan of the lift but it works. I bought the truck without a motor, transmission and transfer case.

I had a 1987 TBI 350 that was rebuilt with a slightly bigger cam and a set of vortec heads and is converted to a carburetor. The transmission is a 1987 turbo 400 with a 208 attached. Both were rebuilt.

The one of many issues I’m working through is the crossmember will not bolt to the frame due to the transfer case hitting the bottom of the cab. There is an approximate 1.5 inch gap.

I’m not sure if they make a shorter mount, a body lift or a spacer to make up the gap.


Sorry about the confusion.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

I'm still lost... What is the frame from? 72 K20 also? Post 5 vs the recurring references to K20 "cab" only are throwin me off. I "think" you're saying you have a 72 K20 cab and 72 K20 chassis into which you're installing the 87 eng/trans/tcase into(?) Just to confirm - your cab VIN starts w/CK and you have a detachable high hump, yes? Where exactly is the interference - just at the t-case (which would make sense). Personally, I'd do some creative bodywork where you have interference rather than a body lift. I like body lifts even less than chassis lifts... (yes, I know, but that's just me... :)) A few pics would help a lot too. Thanks for posting, this is an interesting one! If your only interference is at the t-case (IF), have you considered just getting the TH400 adapter for a 205 and seeking a 205 out? Yes, that could easily run up a tab and you already have a rebuilt 208 already, so I do appreciate the dilemma.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

Ya it’s a 72 cab, Frame and axles. I agree I don’t like the body lift idea either. As of right now this is the main thing holding me back from gettin it running. I would rather keep the 208 right now due to the costs.

I am also thinking of modifying the crossmember to make up the difference. I’ll try to get pics posted soon

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

If I am getting this correct, You can use spacers to attach your member a bit lower. I have run this way for years. This also lessens the angles on the driveshafts when running a lift. I made my own spacer from flat bar and square tubing from Home Depot. I can get you a pic if you like.

Re: 1972 Chevrolet K20 transmission crossmember for a turbo 400.
 

I think the square body cross member raises the transmission and transfer case up a bit and is causing you problems. I tried to use a square body cross member in my 2wd and it raised my transmission closer to the floor board.