Swapping the TH350 with TH400. What to do??

[chevybuilder18]

if im correct, there is all sorts of different factory cross members for our trucks, not to mention all of the wierd sorts different engine and tranny packages put together.. What im trying to say is, is there only one cross member for exhaust and tranny?
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[74 stepside]

Pretty sure the transmission crossmember is the same for 350 and 400 trans. There should be extra holes in your frame so that it can move forward or backwards in the frame for different trans options. Your driveshaft will also need to be changed as the transmissions are different lengths and yokes are different too.

[KQQL IT]

And a kick down wire vs a cable. Which isnt mandatory just convient. Th400 slip toke shorten driveshaft.
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[FlatBlack83]

I am actually in the process of doing this, im replacing the 305/th350 with a 454/th400 I looked into alot of different crossmembers, and also thought about making one to work with the exhaust, I finally decided to go with this one, I understand it is for 67-73 trucks and mines an 83 but I like the fact that it boxed in the frame rails, this strengths the frame. I actually got this off another thread on here,

[clinebarger]

Originally Posted by FlatBlack83

I am actually in the process of doing this, im replacing the 305/th350 with a 454/th400 I looked into alot of different crossmembers, and also thought about making one to work with the exhaust, I finally decided to go with this one, I understand it is for 67-73 trucks and mines an 83 but I like the fact that it boxed in the frame rails, this strengths the frame. I actually got this off another thread on here,

A factory crossmember with the correct brace/s is stronger than that aftermarket crossmember.

Your 83 has a 4wd crossmember, GM started "standardizing" certain parts like the crossmember....The 4wd crossmember went in every truck even 2wd's.

I think they started doing that in '81. Find a earlier 2wd crossmember (3 pieces)....Crossmember & 2 braces & has 2 humps for dual exhaust.

[FlatBlack83]

Originally Posted by clinebarger

A factory crossmember with the correct brace/s is stronger than that aftermarket crossmember.

Your 83 has a 4wd crossmember, GM started "standardizing" certain parts like the crossmember....The 4wd crossmember went in every truck even 2wd's.

I think they started doing that in '81. Find a earlier 2wd crossmember (3 pieces)....Crossmember & 2 braces & has 2 humps for dual exhaust.

Gotch ya! I went with this one because I wanted to run my exhaust above it, I didn't want the exhaust the lowest hanging part. It all depends on what you want, and your application! Clinebarger maybe you could answer another question? Will the driveshaft have to be shortened from going from a 350 to 400?
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[clinebarger]

Originally Posted by FlatBlack83

Gotch ya! I went with this one because I wanted to run my exhaust above it, I didn't want the exhaust the lowest hanging part. It all depends on what you want, and your application! Clinebarger maybe you could answer another question? Will the driveshaft have to be shortened from going from a 350 to 400?
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Most all Truck TH350C's are "long tail" with a 9" tail housing & have a total length of 30 3/4".

Short tail TH400's are 28 3/8" long.

So just a guess without knowing EXACTLY what you have....You driveshaft is a little over 2" short???

Using a TH400 can present another problem.....If it was equipped with a "Bolt-on" yoke....The output shaft needs to be machined down or you need a special Counter Bored slip yoke.

If this is the case go with the counter bored slip yoke.....Machining the ouput shaft will require disassembly of the trans. And you have to buy a slip yoke anyway. http://www.dennysdriveshaft.com/p69_...pline_wth.html

[FlatBlack83]

ok, I did just have the th400 rebuilt and when the guy rebuilt it he swapped it to a slip yoke, I have yet to test the drive shaft because I have been waiting to recieve my crossmember which I got today, hopefully I will be able to do this tomorrow and I will let you know how it goes, but thank you for the information!