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Old 12-04-2008, 06:25 PM   #1
harrdawg54
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Rockwell T221 - NP205 swap

Ok....I read as much as I could about what people did when they did this swap. I used the cross member that came from the donor because I read that it was 1"-1 1/2" lower so it wouldn't rub the floor of the cab. I installed new cab mounts and the t-case still hits the floor. My thought was to cut the floor and weld in a new "humped" piece that is 1" higher than the floor and sits under the seat. I have no pics as my truck is 30 miles away at my inlaws. If you have any better ideas, and no I don't want to go with a body lift, I would love to hear them.
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Old 12-05-2008, 02:22 PM   #2
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Re: Rockwell T221 - NP205 swap

I know some of you have done this swap....I think I am going to cut the floor but any suggestions are welcome
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Old 12-05-2008, 06:23 PM   #3
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Re: Rockwell T221 - NP205 swap

i made the swap this past summer...removed the 3spd/t-221 and replaced it with a 350 auto and np 205..i didnt have any floor problems.. maybe it was the auto transmission and cross member...
my suggestions would be to cut some 1" square tubing about 8" and bore holes and lower the corss member from the frame. that should get it off the floor board...s.
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Old 12-05-2008, 07:08 PM   #4
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Re: Rockwell T221 - NP205 swap

It sounds like you do NOT have a "high hump" cab. The low hump is part of the floor sheet metal. The high hump is bolted in. If it is true that your transmission tunnel isn't bolted in, just buy a high hump off the parts board, cut your low one out, and bolt in the high one.
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Old 12-05-2008, 09:48 PM   #5
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Re: Rockwell T221 - NP205 swap

I do have a high hump cab....the t-case is hitting after the hump near the seat. I thought about adding some square steel to the cross member to lower the t-case(and I still might).
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Old 12-05-2008, 10:44 PM   #6
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Re: Rockwell T221 - NP205 swap

What year was your donor vehicle. Very odd that your hitting the floor. I'm doing this same swap but I have a body lift so I don't have this issue. My thread is over in the 4x4 forum.
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Old 12-06-2008, 12:06 AM   #7
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Re: Rockwell T221 - NP205 swap

I bet you don't have the correct 4x4 cab mount bushings. In my original 67 4wd they don't use the tall bushings just the old 2wd style bushings in the rear. Check those against another 71-72 4x4 or even a 3/4 ton 2WD as they are the same. Might want to try this posting over in the 4x4 section.
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Old 12-08-2008, 01:09 PM   #8
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Re: Rockwell T221 - NP205 swap

the donor was a 1983 chevy 1-ton. I got the tranny, t-case and drive lines. I know the cab mounts are correct because I called gmcpauls and confirmed which ones were correct. I also checked them with the originals. I want to say thank you for all the input. I think I am just going to shim the cross member down.
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Old 12-08-2008, 11:33 PM   #9
red71cheyenne
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Re: Rockwell T221 - NP205 swap

I swapped from a 3 speed to SM465 withe the Rockwell and I'm still pretty close to the floor too. Not touching, but pretty close. I have stock body mounts and haven't lowered the cross member yet, but may in the future. My rockwell is also behind the hump where it is close to touching, but I think this may be due to the change in tranny's.
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Old 12-09-2008, 08:39 AM   #10
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Re: Rockwell T221 - NP205 swap

I'd purchase a 67-72 NP205 cross member off the parts board. No shims and you know it will be factory correct - in other words some engineer in 1968 or 1969 figured out the drive line angles. Using a 1983 1-ton you're kind of rolling the dice.

FYI, ALL 67-72s that came from the factory with a NP205 shared the same cross member. So if the used part salesman says it was a 3-speed/NP205 or a 4-speed/NP205 or a th350/NP205 don't worry, my th350/NP205 is sitting on a 3-speed/NP205 cross member, the one that came originally with my truck. Back then GM made EVERY transmission in front of a NP205 bolt to an adapter that fit the same cross member. GM was doing modular design before anybody knew what modular design was.
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Old 12-10-2008, 02:48 PM   #11
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Re: Rockwell T221 - NP205 swap

The cab is sitting on the rear mounts and is less than 1/2" off of the front. I think I am going to shim the cross member 1" and go from there. I will get some pix posted when I get to work on my truck next.
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