TH400 swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gilby246 · 03-23-2005, 01:43 PM

Sorry if this question has been beat to death. I did a search but didnt find what i need or just didnt put in the correct search words

Anyway
I have a 79 gmc 1/2 ton with a TH350,one peice drive shaft, with a caddy 500. I plan on swapping this to a TH400 but (if i remember right) i think the th400 is a bit longer than the th350 I think I will also need to go with a two piece drive shaft rather than my one peice for the 400??.
If I go with a th400 and a two peice shaft will this bolt right up??

60-66 Nut · 03-23-2005, 02:10 PM

Gilby, it depends on what 400 you use. The only 400's with the bolt-on rear yoke are the Chevy-GMC truck 400's which all have the Chevy bolt pattern(unless you can find one from a 78-81 truck with the Olds diesel) so you will need the BOP adapter to bolt it to the Caddy motor, unless you already have one for your 350 trans. If you could find a 400 from a Buick, Olds, Pontiac or Cadillac car they should have a slip-in rear yoke. The yoke is bigger than the 350 yoke, but you could still use the one-piece driveshaft, even though it would still have to be shortened. Also, a Buick, Olds, Pontiac or Cadillac 400 would bolt on without an adapter, unless it had a Chevy engine, which many of them had in the late seventies-early eighties. If you do use the 400 with the bolt-on rear yoke and two-piece shaft, don't forget the bracket that the hanger bearing bolts to. Hope that helps.

60-66 Nut

gilby246 · 03-23-2005, 03:12 PM

60-66 nut

I already have the th350 bolted to the caddy using the adpater plate for the bolt pattern. This tranny has very imited time behind this motor.

There is a th400 out of 80 chevy 2wd truck with a short shaft that I can pick up cheep. A th400 can handle these engine so I would like to put one in asap. I dont want a cad th400 cause the shifting is allot smoother in those due cadillac trying to make a smoother ride.

I have never had the pleasure of swapping one style tranny for another so im working with limited knowledge on this part.
I know its possible (anything is), just was wondering what will need to be done to make it happen and the easiest way to do it

03-23-2005, 01:43 PM	#1
gilby246 Registered User Join Date: Mar 2005 Location: seattle Posts: 24	TH400 swap Sorry if this question has been beat to death. I did a search but didnt find what i need or just didnt put in the correct search words Anyway I have a 79 gmc 1/2 ton with a TH350,one peice drive shaft, with a caddy 500. I plan on swapping this to a TH400 but (if i remember right) i think the th400 is a bit longer than the th350 I think I will also need to go with a two piece drive shaft rather than my one peice for the 400??. If I go with a th400 and a two peice shaft will this bolt right up??

03-23-2005, 02:10 PM	#2
60-66 Nut Professional Beer Tester Join Date: Aug 2004 Location: Louisiana Posts: 453	Gilby, it depends on what 400 you use. The only 400's with the bolt-on rear yoke are the Chevy-GMC truck 400's which all have the Chevy bolt pattern(unless you can find one from a 78-81 truck with the Olds diesel) so you will need the BOP adapter to bolt it to the Caddy motor, unless you already have one for your 350 trans. If you could find a 400 from a Buick, Olds, Pontiac or Cadillac car they should have a slip-in rear yoke. The yoke is bigger than the 350 yoke, but you could still use the one-piece driveshaft, even though it would still have to be shortened. Also, a Buick, Olds, Pontiac or Cadillac 400 would bolt on without an adapter, unless it had a Chevy engine, which many of them had in the late seventies-early eighties. If you do use the 400 with the bolt-on rear yoke and two-piece shaft, don't forget the bracket that the hanger bearing bolts to. Hope that helps. 60-66 Nut __________________ 60 Ford F100 Custom Cab 61 Apache Short Fleetside 64 C10 Short Stepside 65 C80 409 V8 5spd(X-Firetruck) 83 GMC 350 Olds Diesel 85 GMC Short Bed 86 GMC Short Bed 90 GMC R3500 Crew Cab 92 GMC 1500

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03-23-2005, 03:12 PM	#3
gilby246 Registered User Join Date: Mar 2005 Location: seattle Posts: 24	60-66 nut I already have the th350 bolted to the caddy using the adpater plate for the bolt pattern. This tranny has very imited time behind this motor. There is a th400 out of 80 chevy 2wd truck with a short shaft that I can pick up cheep. A th400 can handle these engine so I would like to put one in asap. I dont want a cad th400 cause the shifting is allot smoother in those due cadillac trying to make a smoother ride. I have never had the pleasure of swapping one style tranny for another so im working with limited knowledge on this part. I know its possible (anything is), just was wondering what will need to be done to make it happen and the easiest way to do it



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