[Gearhead forever]

I was talking to a guy who said I could swap a TH400 in place of my TH350 and keep the same driveshaft by swapping the tail shafts. Is this correct? Any Idea on how much it would cost to rebuild one of these for some mild "go" for towing and a bit of thrashing if I did the work myself?

[jimfulco]

Not true. They are totally different transmissions.

[M&M CUSTOM]

If you get right down to it, with the three different lengths of both of those transmissions, you can get the length very close.
The TH-350 tailshaft lengths are 6", 9", & 12" with a main case length of 21 5/8"
The TH-400 tailshaft lengths are 4", 9", 13", with a main case length of 25"

A TH-350 with 9" tailshaft and a TH-400 with a 4" tailshaft ore only 3/8" inch difference and,
A TH 350 with a 12" tailshaft and a TH-400 with a 9" tailshaft are only 3/8" inch different in length.

BUT, the output shaft of each of these series transmission is completely different and will not swap to the other transmission.

You CAN, however swap the slip yoke on the driveshaft to allow the other transmissions' yoke to work in it's place. If not directly, then with the use of a "conversion" universal joint.

[Gearhead forever]

Thanks Matt: I'm still undecided on what to do. I was thinking of converting to a 4-5speed, but I have enough work do do on the rest of the truck already.....I'm back to thinking of rebuilding one of my auto tranny's. Is there really much advantage to replacing my TH350 with a 400 anyway? The most power it will see is 350-400 hp, and maybe up to 450lbs of torque at best....Any thoughts?

[M&M CUSTOM]

A good rebuild with the right improvements and the 350 is as good or better than the stock 400 trans. And the transmission will hold that amount of power.

In stock form it takes almost 1½ times the power to turn the 400 as compared to the 350.

If the transmission gearing makes a difference to you the TH-350 has 2.52/1.52/1.00 to one gears, and the TH-400 has 2.48/1.48/1.00.

Other members here have tackled the transmission rebuilding themselves, and had success along with saying that they could do it, and saved hundreds while doing it.

[k-star]

Has anyone else seen the th-400 with the th-350 out put shaft???? I have seen 2 of them but both were in the bop cases..

Keith

[M&M CUSTOM]

Originally Posted by k-star

Has anyone else seen the th-400 with the th-350 out put shaft???? I have seen 2 of them but both were in the bop cases..

Keith

I wouldn't doubt it being in the BOPC case, I also heard of some dual bellhousing bolt pattern TH-350 cases. If you have pictures of either of these I will put them in my sticky post.

[k-star]

The one i owned i took apart. I'll look to see if i still have the parts in stock. Maybe i can assemble them quick just to get a pic....

I need a good th-400 core for a rebuild and i just ran across the second one with the th-350 out put shaft at a swap meet a few weeks ago.... I didn't buy it because i need a chevy case...

keith

[Gearhead forever]

Great..thanks. I'll be ditching the 400 then.