72 th350 np203 swap to th400 np205

[dieselfuel007]

i've currently got a mild 454 engine th350 np203 in my 72 k10 i'm restoring the engine is moved 2 inches forward driveshafts have been shortened in the front lenghtened in the rear well now i'm considering swaping my driveline out for a th400 np205 out of a 79 k20 i guess i'm looking for anyone thats done this before to see what all its going to take to make it work

[jjzepplin]

Is the 400 already mated to the 205? That's the biggest issue.

[special-K]

Do you have measurements of both from engine/bellhousing mating surface to yoke on transfer case? So you still have the slip-yoke on the 203 tail? Got pictures at least? I assume the '79 NP205 has the fixed yoke. I'm not familiar with your set-up in there now. M=Never seen anyone put a 203 in a '72 before. Where is the crossmember located, original position?

[dieselfuel007]

the th400 and np205 are together my current np203 is fixed yoke i've already swaped it to 1350 u joints i just didn't know if anyone had done this swap already and what they had to change

[kwmech]

It is all bolt up stuff. Remove the 350/203 combo. Bolt in the 400/205. The trans lines will bolt up with just a little manipulation. torque convertor will bolt up -no issues. You may/will have to drill the frame for the x-member moving back (that will probably be the biggest deal). T-case shifter hole will move back a little, so a floor pan cut and repair (covered by carpet). Shifter from column will bolt up with a small adjustment. Driveshafts both front and rear rebuilt. Overall it is a pretty easy deal

[57taskforce]

Everyone else already gave good advice here, all I can say is you probably won’t regret ditching the 203. The other thing your also gonna have to address is the electric kick down switch for the th400, again another easy hurdle to cross.

[dieselfuel007]

whats the kickdown amount to just a switch on the carb linkage that tells it when its wot?i'm i kind of go shape i guess cause i could probably just move the crossmember back where it was and i've got a b&m floor shifter thats cable controlled just sucks i have my driveshafts the right lenght for my current setup

[gmc684x4]

The np203 case is from a 73 up square body truck 67 to 69 our trucks used a rockwell case some 69s may have had a np205 stock
70 72 have np205 as stock transfer case
T400 better tranny and np205 are fairly bullet proof

Stock engine placement for 67 72 k series trucks is the back set of engine mount holes

The reason behind this is so the diff does not have clearance issues with either the cross member or the oil pan

Talking with my cousin on his 69 big block build he kept it in the back frame holes for two reasons center the weight more and to have more header clearance

[kwmech]

Originally Posted by gmc684x4

The reason behind this is so the diff does not have clearance issues with either the cross member or the oil pan

A 2.5 lift will resolve this issue as most of these trucks have a 4''. but yes it is something to take note of

[1976gmc20]

Originally Posted by dieselfuel007

whats the kickdown amount to just a switch on the carb linkage that tells it when its wot?i'm i kind of go shape i guess cause i could probably just move the crossmember back where it was and i've got a b&m floor shifter thats cable controlled just sucks i have my driveshafts the right lenght for my current setup

Well ... you could get one of those adapters to mate a 203 gearbox to a 205 and have a three speed, very deep reduction transfer case

[57taskforce]

The kickdown switch mounts on the gas pedal mount bracket On the 67-72 trucks. Yea basically it tells the transmission to grab another gear when you mash the skinny pedal.

[dieselfuel007]

well scratch that it wasn't a turbo 400 is was a turbo 350 he didn't know what he had

[1976gmc20]

Originally Posted by dieselfuel007

well scratch that it wasn't a turbo 400 is was a turbo 350 he didn't know what he had

So are you still going to swap in the NP205 ?

[jocko]

Don't let that 205 get away! Buy the combo if you have to and you'll have a spare TH350 lying around - you know to sell that NP203 with

[57taskforce]

Originally Posted by jocko

Don't let that 205 get away! Buy the combo if you have to and you'll have a spare TH350 lying around - you know to sell that NP203 with

That’s the best advice of this thread!