Swapping Turbo 400 in 1980 Stepside

[TexasStepside]

Question - I have swapped a 454 into my 1980 Stepside that was originally a 250/TH350 combo - I retained the TH350 just to get the truck mobile. I want to swap in the TH400 that came with the donor truck (1978 1/2 ton, LWB) but I noticed that the carrier (center) bearing for the two piece driveshaft from the donor truck mounts to a crossmember that also doubles as the rear cab mounts - my Stepside does not have this crossmember, but rather just the mounts for the rear cab. I am planning to transfer this donor truck crossmember and shorten the piece of the driveshaft from the carrier bearing to the rear axle. I am assuming that this is the way the factory setup is with a TH400 in a SWB truck. Any information, pictures of this would be appreciated.

[greg64]

Well, there may be other opinions on this, but here's mine. The swb trucks don't need a two piece driveshaft. If I were you, I'd get a new shaft made with the turbo400 yoke on one end, and the necessary axle ujoint on the other. Leave the lwb crossmember out.

[Slammed84]

Just what greg64 said!
I robbed my 400 from a c20 also. I went to a salvage and got a LWB driveshaft and had a local driveshaft shop frankenstein one together for me. They just shortened it and put the 400 yoke on it.

[Titomars]

Originally Posted by TexasStepside

Question - I have swapped a 454 into my 1980 Stepside that was originally a 250/TH350 combo - I retained the TH350 just to get the truck mobile. I want to swap in the TH400 that came with the donor truck (1978 1/2 ton, LWB) but I noticed that the carrier (center) bearing for the two piece driveshaft from the donor truck mounts to a crossmember that also doubles as the rear cab mounts - my Stepside does not have this crossmember, but rather just the mounts for the rear cab. I am planning to transfer this donor truck crossmember and shorten the piece of the driveshaft from the carrier bearing to the rear axle. I am assuming that this is the way the factory setup is with a TH400 in a SWB truck. Any information, pictures of this would be appreciated.

Actually you do. The crossmember is the same your truck. It just does not have the center support bracket on it. if you were to look closely you should see 4 holes in it where the bracket goes. With that said SWB trucks with automatics did not use 2 piece shafts. The correct TH400 in a SWB 1/2ton is a long tailshaft with a 32 spline slip yoke. The C20 and C30 used a short shaft with bolt in yoke. The short shaft TH400 will work. With a slip yoke or if you use the bolt in yoke you just have a drive shaft made with a slip yoke in it instead of the trans.

[TexasStepside]

Titomars - thanks for the response - I notice that you have a 77 stepside with a factory 454/TH400 - any chance of getting some pictures of the setup of you have? Thx

[Titomars]

Originally Posted by TexasStepside

Titomars - thanks for the response - I notice that you have a 77 stepside with a factory 454/TH400 - any chance of getting some pictures of the setup of you have? Thx

I can take some pics for you. Mine is not 100% stock/correct yet. When I bought her the original owner swapped in a 700R4. Which proceeded to get blown up. The original TH400 was long gone. When I bought it I dragged it home. I bought a TH400 off C/L. but it is a bastard build. A 4X4 case with a car long tail housing and shaft, and no provision for a speedo. Working on finding the correct TH400 for mine.

[snaptoo]

My trans guy built me what he called a TH 375 , used a BOP output shaft and housing and uses a small dia. yoke but it was a long slip really worked out well !!

[USSkoval]

There's more than a couple ways to skin this cat.

I replaced my shortbed's th350 with a th400 from a heavier truck (short tail, bolt-on yoke). I simply used my stock th350 shaft with a long slip style yoke from a 4x4 Burb (had the np208). I also unbolted the fixed yoke that came on the th400. It worked out perfect, the longer yoke made up the difference of the shorter trans and it slid right into place.