Bell housings, flywheels, and trans, oh my

[al's71gmc]

I'm in the process of putiing a mid 80's 350 in a 72 gmc 4x4. The doner truck has a th 400. I have the bell housing and flywheel for the sm465 from the original 350 engine. Will they bolt right up to the later model block?

And can I use the th400 to replace a th350 in a different truck? The th400 is in a 2wd truck, and it would be going into a 71 4wd. Is the th350 adapter for the np205 the same as the th400? I will have the bellhousing and flexplate from the th400, if needed.

Is there any advantage to switching the th350 out with the th400? My main reason for considering the swap is that the th350 has about twice the mileage and leaks pretty bad.

Thanks, Al

[Bowtie67]

The only real problem you will have switch to a later model block is if it has a single rear main seal, the older small blocks use a different flywheel. One other potential thing maybe that some of the later model blocks dont have the capabilities for a mechanical fuel pump. Bellhousings for all small blocks are the same, TH350,Th400, 700r4, 200r4, powerglides, etc all have the same bolt pattern. I have both sets of flywheels setups and some clutches here. You cant even by a flywheel for these prices.

http://67-72chevytrucks.com/vboard/s...d.php?t=188431

[al's71gmc]

Thanks Bowtie67. I'll look more closely at the setup. This engine is in a 2wd 70 gmc now, with the th400 behind it. The PO said it is a mideighties engine. It has the serp belt setup. It's going into a 72 4wd and I want to use the 4sp manual/np 205 from the 72. I just don't know if I can bolt everything back up.

[al's71gmc]

Help. Anyone?

[lvscott]

i believe the output shaft is different on 2wd v.s. 4wd transmissions and because of this they don't interchange. the advantage to the th400 is that it is alot stronger trans.

[Bowtie67]

Originally Posted by al's71gmc

I'm in the process of putiing a mid 80's 350 in a 72 gmc 4x4. The doner truck has a th 400. I have the bell housing and flywheel for the sm465 from the original 350 engine. Will they bolt right up to the later model block?

And can I use the th400 to replace a th350 in a different truck? The th400 is in a 2wd truck, and it would be going into a 71 4wd. Is the th350 adapter for the np205 the same as the th400? I will have the bellhousing and flexplate from the th400, if needed.

Is there any advantage to switching the th350 out with the th400? My main reason for considering the swap is that the th350 has about twice the mileage and leaks pretty bad.

Thanks, Al

First one already answered, All v-8 and most 6cyl bell housings auto/manual will bolt up to with either a straight 6, V6 or V8 motors except the very pre 60's 6cyl, these blocks had a different bolt pattern, they actuually required pulling the flywheel off before remove the bellhousings, never dealt with to many of the early auto, except they where extremely heavy.

Second one is the 400 does have a different output shaft. The flywheels and tourque converters are the same with the exception of the model year of the 350 using a single rear main seal vs the 2piece rear main seal. The single main seal is easily identifiable by looking at the rear of the block and there will be an aluminum housing there for the seal and can be replace without pulling the oil pan. The 2 piece you have to drop the pan to replace.

Third. The 400 was primarrily for big block engines, there is more drivetrain loss with a 400 than a 350. If the 350 leaks when you pull it and want to reuse it do a tranny service on it, put in a new rear seal and front TQ converter seal.

[al's71gmc]

Thanks Bowtie67- I'll check out the rear main tomorrow. And thanks lvscott.

[Americanrider]

And can I use the th400 to replace a th350 in a different truck? The th400 is in a 2wd truck, and it would be going into a 71 4wd. Is the th350 adapter for the np205 the same as the th400? I will have the bellhousing and flexplate from the th400, if needed.

4wd trannies do not have tailshafts, a 2wd tranny will not work in a 4wd without modification or using a divorced-style transfer case. 4wd AT's are know as K-cases since their application was for K-type trucks & blazers.

The pics are:
72 Th350 from a K20 truck
the different types input shafts of NP 205's

the 2 on the left are th400 (New & old style)
center is SM 465
right is th350

The rear output shafts on 4wd trannies are all different:
SM 465 is a 10 coarse spline
Th350 is a fine 27 spline
Th400 is a fine 32 spline

When swaping NP 205s with trannies you will need to match the tranny output with the transfer case input. You can do your research here on NP 205's

http://www.offroaddesign.com/NP205tech.htm