TH 350 vs 400 turbo for my ’78 Chevy C10 Scottsdale

[ammco220]

I recently bought a 1978 Chevy C10 4x4 “Heavy 1/2 ton” 350 V8 Turbo 400
“Less that 2,000 miles on crate motor and trans re-build” according to the sign in the window. Paid $3100 cash. Of course, about a month after I bought it, the transmission blew out.

Now, I hadn’t been driving it too hard, just a few camping trips and used it to move. Probably only put another 500 miles on it. This truck is my hunting/camping/firewood truck, not my daily commuter. I do want it to keep it for a while and maybe eventually put some larger tires on it and a cap. So I want it burly/heavy duty, like it supposed to be.

I hired a “mobile mechanic.” He came over and diagnosed the problem. He recommended we drop the tranny and bring it to a transmission shop, have them rebuild it, and then we put it back in at my house. Sounds good, but I had to diversify my options.

So, I went on Craigslist and I found a guy who was parting out a late-80s 2wd Chevy van, the engine from which he had put into his 80-something Chevy truck. Turns out we shared the same profession, so I dont think he ****ed me over. But who knows? It is craigslist after all. I bought a working turbo 400 + torque converter for $250 from this guy.

Anyhoo, the mobile mechanic and I dropped the transmission ONLY TO DISCOVER that when the truck was rebuilt they put a TH350 in it instead of a 400. The 350 looked like it had recently been rebuilt (or at least spray painted). My craigslist 400, however, was too long (by about 3 inches) to just be plopped in the truck and have me good to go.

Now here’s my dilemma, do I:
1) sell off the craigslist 400 turbo and bring the 350 into a transmission shop and have it rebuilt again, or
2) Do I have the driveshaft modified and buy the necessary parts to have my truck accept a 400 (from a 2wd) and plop in my craigslist tranny?

My main concerns are
1) the dubious nature of a craigslist auto part, and
2) did the 350 blow out because it was inadequate for the make & model of my tuck?

[cableguy0]

Since you already bought the th400 I would go with it. Having the driveshaft shortened isn't terribly expensive. Most places will shorten,balance and install all new u joints for around 100 bucks. The th400 is a seriously strong trans. The th350 you broke was probably worn out in the first place. A th350 would probably work fine in your application with a shift kit and upgraded sprag but the stock th400 is still stronger than the upgraded th350. The th400 and th350 would cost about the same to have rebuilt. So that is a wash. Parts are cheap for both and torque converters interchange.

[cadillac_al]

How does the fluid look in the 400? I have never killed one so I would be inclined to run it as is. It would be nice to hook up the electric passing gear on the 400 to have it working perfectly. I swapped one in a 2wd truck 20 years ago and didn't bother with the passing gear and it worked fine but I was younger then. Nowadays I like things to be perfect.

However there really is nothing wrong with a good th350. Both of my 4x4's are running th350's. I mud bogged one of them for a few years with no problems and my current driver is original with 160k miles on it; and it has towed a lot of trailers. If the th400 had brown fluid and definitely needed a rebuild then it might be easier to rebuild your th350 and you will still have passing gear.

[donut]

IMO, keep the 400. Flip side, did the CL guy have the driveshaft?

[geezer#99]

I'd do 2 things.
First and most important! Find a new mechanic who can tell a t350 from a 400.
Second. Take the t350 to a tranny shop to check it out. Rebuild it if necessary.

[clinebarger]

A 1978 4wd SBC C-10 would of had a TH350 from the factory, Heavy-Half or not.

A TH350 will work fine if built correctly, Your truck being 4wd complicates switching over to a TH400.

Upgrading the intermediate sprag race, Replacing ALL bushings, & Dual feeding the directs on top of a full rebuild does wonders for a TH350.

[cableguy0]

Good catch cline I completely missed that it was a 4wd.. In that case 100% your better off having someone rebuild the th350 and selling your th400. 4wd trans swap is a pita.

[donut]

Yep, I missed the 4wd C-10 also.
Agree with the experts, the swap from a tbh350 to a 400 in a 4wd is much more complicated.

[ElectricDan]

I have a 72 C10 pickup with a 383 stroker with a 350 turbo
Tranny, got a 400 turbo recently rebuilt at a very good price
Will the 400 fit ok? other than the drive shaft . And
How much trouble is the electric passing gear to install
Posted via Mobile Device

[kwmech]

Originally Posted by ElectricDan

I have a 72 C10 pickup with a 383 stroker with a 350 turbo
Tranny, got a 400 turbo recently rebuilt at a very good price
Will the 400 fit ok? other than the drive shaft . And
How much trouble is the electric passing gear to install
Posted via Mobile Device

Back from the dead thread....400 install in a 2wd is more straight forward. X-member moves back about 1.5'' new driveshaft. Everything from the 350 bolts up. Same lines, same shifter etc. How often do most people use the 'kick down'/passing gear. Kick down switch bolts to the accel pedal bracket under the dash. One wire to the trans and the other to the fuse block, pretty simple

[GASoline71]

Originally Posted by kwmech

Back from the dead thread....

Yep... and I really miss cableguy and clinebarger...

Gary

[kwmech]

Yup, same here. I could really use Clinebargers help with this issue I'm having with my 4L80

[cadillac_al]

Originally Posted by GASoline71

Yep... and I really miss cableguy and clinebarger...

Gary

I think the administrators should send them some Christmas cards this year and try to entice them back here. I miss their knowledge too.