TH400 NP205 Swap in 73 K5

[xissix]

I just spend a couple hours searching old threads and couldn't find an answer to my issue, so hoping someone can help.

Truck is a 73' K5, 350/TH350/NP203. I finished pulling my TH350/NP203 out and putting in a TH400/NP205 (figure 8 adapter) tonight. Problem is the cross member for the trans/t-case that locals say should work is causing the 205 to hit the bottom of my cab. Cross member has about a 1" drop and has a relief for the front drive shaft (was told it came out of a K20 suburban, not sure on year). Looks like I need to be at least 2" lower than it is, does this sound right to anyone? Is the 73" K5 different from others?

My 203 cross member has about a 3" drop to it, but no relief for the front drive shaft. I don't mind cutting it, but want to be sure my output angles are ok, how can I tell if they are off? Does the trans pan need to be somewhat level?

Thanks for any help!

 

[doop300]

I did the same swap with my 83 blazer and also an 86 shortbox, on both times we used a different crossmember, I dont know much about the exact ones we used as we have a pile of them, so Im not much help there but I know there was a relief in the crossmember for the output shaft of the 205 that the others didnt have. So if you can find the right crossmember for the job your set, otherwise you'll have to customize your own.

 

[JDNobodi]

The NP 203 cross member has the right amount of drop. It sounds like they sold you a cross member for a later model "short" adapter.
For my TH400/NP205 combo, I used a TH350/NP205 cross member. A 465/NP205 should be the same. I had to drill new holes in the frame though. One problem with mine though is the front drive flange hits the cross member at high torque. It is self-clearance now but a spacer (1/4") under the mounting foot would have solved that problem.

Now sometime the 203 cross member is different. I've seen two different style of cross members, one with both holes the same size for the rubber bushings and the other cross member with one hole more slotted. The later one you can use for you application. If both holes are the same size, you going to have to slot one hole bigger to the middle.

 

[xissix]

My 203 crossmember doesn't have a slot, so I guess I'll have to do a couple thing to it to get it to work. How bad would it be to run a piece of 2" square tube on each side to space down the one I have?

 

[JDNobodi]

You don't think it be easier to slot the hole?

I think this cross member is from the late seventies to early eighties. It has a notch in it for the drive flange. The earlier NP203 and NP205 have the constant velocity joint with a yoke which is smaller.

 

[xissix]

Thanks for the pic, that looks similar to the crossmember I have, do you know how much it drops?

I spent about an hour working on the 203 crossmember this morning before I finally gave up. Both of the holes needed to be ovalled out (mount needs to be centered), plus the passenger side needs relieved about an inch for the front driveshaft. I did get it temp mounted up and it causes the distibuter cap to hit the firewall For now I built a couple quick 1 inch spacers just so I could bolt it up and get driveline lengths meaured.
Problem is I have about 1/4 of space above the t-case, and only 1/4 of space to my distibuter cap (running HEI).
I think I'm going to build a new bracket from scratch and run some poly bushings. Need to somehow keep the combo from moving too much and making noise. I guess I could get out a double jack and make space

If I were going factory, looks like I need about a 2 1/2 inch drop bracket, do those even exist?

 

[JDNobodi]

Damn, I can't believe you are having so many problems.
As for the firewall clearance for the HEI, I think the firewall is closer to the motor on a 73 than on a 74 because 74 is the first for HEI. I wish I still had my 73 so I could measure it.

Anyway, from the top to the bottom, I measured 3 5/8. From the top to the top where the mounts goes, 2 1/4.

When I was measuring the cross member, I noticed the previous owner had it on backwards. The flange from the front output ground itself a huge relief in the cross member.

Um, I don't think you need to slot both holes because on the 203, one hole is offset. Measure from the side and make the hole the farthest out in the same amount as the other hole.

 

[xissix]

Yeah it's strange for sure. I did this to a 75 a few years ago and it was nearly a direct swap (needed to drill 2 holes). I think that you may be onto something with the differences for HEI years.

Hmm, that's odd, my supposed correct crossmember measures 1 1/4 from top to top, my 203 is right at 3 inches. It's the one with the upper mounts as well, maybe they are different? Sounds like the one you have is the one i need.

The 203 crossmember isn't offset, both holes measured the same from edge to edge. I read they were offset, so double checked it, even layed the 205 crossmember on it and sure enough they arent.

Talked to a buddy and he thinks he has the crossmember you have, I'm going to take a copy of you pic over and see if it matches (thanks again for that pic, may be my saving grace). Would definately save me from a couple more hours making a new one.