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Are all TH350s the same?

M

meanboyjr

1/2 ton status
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Here's the scoop: I bought a '76 K5 with the 350/TH350/NP203 combo a few months ago for cheap, mainly because I've always wanted one. The truck needs work, but it was complete driver, with just a little rust in the rockers. Anyway, a few weeks ago the trans started slipping and now I only have 1st and 2nd gear, with Park...no 3rd and no Reverse.

Not a big deal, I thought, since I have a junker '81 GMC G20 (3/4 ton) van with the 350/350 combo in it. I'll just "drop and swap" the trannies, right? I've got one sitting there, so why not use it? It's free...

Never having done this before, I searched the forums and learned a lot of good stuff, but I couldn't find the exact answer I was looking for - will ANY TH350 swap for ANY other TH350, regardless of the year and application?

I know I'll need a transmission jack to get the heavy stuff back into place, but are there any other tips on making this job easier & smoother? Other than bringing it to a shop? :wink1:

On a related note, I like the NP203 just fine, but I've been thinking of adding a MileMarker P/T kit while the tranny and transfer case are already out. Any input? Should I leave it full time or not? I'm not planning on doing any serious wheeling, and it won't be a DD - mainly a weekend use, FS road, hunting/fishing/camping rig with the occasional trip down to the Oregon coast. Will the P/T kit allow for slightly better gas mileage?
 
as long as the newer 350 tranny is not the 350C which has lock up it will work with no problem. also the van has a two wheel drive tranny so you would have to change the output shaft
 
cant use the van one in a 4x4

have to have the tailshaft swapped

trade it for a 4x4 one or have it converted

4x4 ones have no tailshaft housing

and have very short tail shaft

unlike 2wd ones

in which there were three different lengths of


good luck
 
1979jimmy350 said:
as long as the newer 350 tranny is not the 350C which has lock up it will work with no problem. also the van has a two wheel drive tranny so you would have to change the output shaft
Click to expand...
Non-lockup TH350C here, from a 1973 Carlo. And yes I did the shaft conversion:hack:
 
The part time kit will make the truck easier to turn in slow corners, but you won't see a lot of improvement in gas mileage.
 
Thanks for the info, fellas.

Roadnotca - are you running the TH350C without the lockup plugged in?

Also, I'm guessing I can swap the output shaft from the tranny that's already in the Blazer...
 
roadnotca said:
Non-lockup TH350C here, from a 1973 Carlo. And yes I did the shaft conversion:hack:
Click to expand...

TH350C *is* lockup, TH350 is not. Can't recall when they came out with the TH350C, either late 70's or early 80's, but not '73.

They don't seem to have a problem being run without lockup (unlike some of the 700's) but I'd be looking for additional cooling either way.

The converter is not interchangeable between a TH350 and -C, so something else to consider.
 
dyeager535 said:
TH350C *is* lockup, TH350 is not. Can't recall when they came out with the TH350C, either late 70's or early 80's, but not '73.

They don't seem to have a problem being run without lockup (unlike some of the 700's) but I'd be looking for additional cooling either way.

The converter is not interchangeable between a TH350 and -C, so something else to consider.
Click to expand...
8 hrs. until I can check my info. :haha:
 
meanboyjr said:
Roadnotca - are you running the TH350C without the lockup plugged in?Not so sure if its a "C", later

Also, I'm guessing I can swap the output shaft from the tranny that's already in the Blazer...I cut my output shaft
Click to expand...
ttt
 
http://www.drivetrain.com/transautogmapp.html

Maybe that will save you the hassle. They show the years there.

Not that internet info is always right, but since the TH350C was only used in a few years of the C/K trucks, I will *guarantee* that it wasn't used as early as 1973. :)

Don't be confused by the various early 70's (and up) emissions/spark control variants out there that will also have electrical plugs on them.
 
dyeager535 said:
http://www.drivetrain.com/transautogmapp.html

Maybe that will save you the hassle. They show the years there.

Not that internet info is always right, but since the TH350C was only used in a few years of the C/K trucks, I will *guarantee* that it wasn't used as early as 1973. :)

Don't be confused by the various early 70's (and up) emissions/spark control variants out there that will also have electrical plugs on them.
Click to expand...
Like I say, it'll be 8 hrs. until I can check it out. My tranny is totally hydraulic, no electrics. :D
 
Thanks Dorian. I did check that website http://www.drivetrain.com/autotranscrossref.html previously and they called out the TH350C for my '81 GMC van (the tranny donor). According to just about everything I've been able to find, the location of the lockup harness/plug-in is right where it should be, so I'm guessing it is indeed a TH350C. Without pulling it and taking a look at the torque converter, I won't be able to tell for sure, but by then...well, I might as well just have found the correct rebuilt tranny somewhere and slapped it in.

All this effort just to save a couple o' bucks! :)
 
Ah, my book says mine's a TH350.:crazy: I still need to crawl under to look at fitting the aluminum TC-cover, I'll check markings then.:confused:
 
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