TH-400 w/Carrier Bearing?

[KCKKen]

Hi Everyone!
Went over to look at parts on the second 85 GMC I have (parts truck), crawled under the side and see that it has a TH-400 with a 2-piece driveshaft. Because this truck initially had a Vortec V-6 in it I'm now guessing that both the engine and transmission have been replaced in it, and the driveshaft was part of the swap.

Because I'll be using a BOP TH-400 (switch-pitch) behind the Olds 350 in my truck project I want to see if this driveshaft will work in my case. The glovebox decal says this truck originally had a 2.73 rear gear in it, now I'm questioning if that's there or something else. How common is the 2-piece driveshaft, and would it be better in a setup what will be doing a lot of trailer towing?

Thanks in advance for any assistance you can offer -- almost ready to take the suspension off of the truck that's being rebuilt for thorough cleaning and bushing/ball joint replacement.

Take Care,
KS

 

[bucket]

A lot of long bed 2wd trucks and 2wd Suburbans had a two piece driveshaft.

 

[AuroraGirl]

Hi Everyone!
Went over to look at parts on the second 85 GMC I have (parts truck), crawled under the side and see that it has a TH-400 with a 2-piece driveshaft. Because this truck initially had a Vortec V-6 in it I'm now guessing that both the engine and transmission have been replaced in it, and the driveshaft was part of the swap.

Because I'll be using a BOP TH-400 (switch-pitch) behind the Olds 350 in my truck project I want to see if this driveshaft will work in my case. The glovebox decal says this truck originally had a 2.73 rear gear in it, now I'm questioning if that's there or something else. How common is the 2-piece driveshaft, and would it be better in a setup what will be doing a lot of trailer towing?

Thanks in advance for any assistance you can offer -- almost ready to take the suspension off of the truck that's being rebuilt for thorough cleaning and bushing/ball joint replacement.

Take Care,
KS

a 85 gmc didnt have a vortec v6 but it did have the 4.3l v6 which later got named a "vortec"

I believe it would have come stock with a th400 and it has the same bellhousing as a sbc(305, 350)

2 piece driveshaft would be used when fixed rear output was used, driveline angle(s) would demand it, and I believe speeds/thus balance were part of it. If you have a th400 switch pitch thats slip yoke you probably want to keep your current driveshaft. you probably wont be too far away from the current driveline, so may be the one you need. if its fixed output you could go to one.

 

[Grit dog]

a 85 gmc didnt have a vortec v6 but it did have the 4.3l v6 which later got named a "vortec"

I believe it would have come stock with a th400 and it has the same bellhousing as a sbc(305, 350)

2 piece driveshaft would be used when fixed rear output was used, driveline angle(s) would demand it, and I believe speeds/thus balance were part of it. If you have a th400 switch pitch thats slip yoke you probably want to keep your current driveshaft. you probably wont be too far away from the current driveline, so may be the one you need. if its fixed output you could go to one.

No, the little motors, especially in half tons came with Overdrive transmissions in the 80s.
Definitely did not roll off the the line with a 6 banger in front of a turbo 400.

 

[Vbb199]

Seems likely a 700r4, th350 or a 4 speed manual would go behind a v6 from the factory.

A th400 would eat the entire 150 hp the v6 made just to rotate the internals
(Sort-of sarcastic, sort of not)
Unless it had like a 3.73 rear gear lol

That 1st gear of the th400 is really unforgiving unless there's enough powa to rotate it

 

[bucket]

No, the little motors, especially in half tons came with Overdrive transmissions in the 80s.
Definitely did not roll off the the line with a 6 banger in front of a turbo 400.

Actually, they 100% did. The 3-speed auto was still the standard auto trans and the th350 was out of production at that point, so they got the th400.

Several members here have had the 4.3/th400 combo in stock form.

 

[AuroraGirl]

Actually, they 100% did. The 3-speed auto was still the standard auto trans and the th350 was out of production at that point, so they got the th400.

Several members here have had the 4.3/th400 combo in stock form.

Thank you.. I was about to say I **** a lot of things up but That was something 100% The reality. the standard powerteam on the appropiate year 80s truck on half ton was literally 4.3 and th400 since the 3 speed on the column I think went away with the i6 going away

 

[AuroraGirl]

Seems likely a 700r4, th350 or a 4 speed manual would go behind a v6 from the factory.

A th400 would eat the entire 150 hp the v6 made just to rotate the internals
(Sort-of sarcastic, sort of not)
Unless it had like a 3.73 rear gear lol

That 1st gear of the th400 is really unforgiving unless there's enough powa to rotate it

Cheap.


TH400 existed for many years and was probably under less demand than ever before because of the 4 speed overdrive manual (Tremec or something?) and 700r4 on the scene.
THe 4.3 and TH400 dont seem logical but the base models before were 3 speed manuals and i6. not best on gas but cheapest to produce. also this is a thought but the mileage was poor and power low, those were things you tried to upsell since gasoline wasnt like this very moment where a 3 speed v6 wasnt a non starter for someone looking for a truck. but Im not someone who was alive and buying a truck then lol but i do know the attitude/atmosphere around them is far different than then

 

[Grit dog]

Thank you.. I was about to say I **** a lot of things up but That was something 100% The reality. the standard powerteam on the appropiate year 80s truck on half ton was literally 4.3 and th400 since the 3 speed on the column I think went away with the i6 going away

Just for giggles I looked it up. Unless the GM Tech specs are wrong, the 1985 1/2 ton 4.3 optional trans was an automatic. And it was the MX0 option, which is a 4sp auto w/ OD.
Maybe other years had a TH400, but considering the 85 was the first year of the 4.3, it doesn’t make sense to me that 86 or 87 models would go backwards in fuel economy and efficiency.

 

[AuroraGirl]

1987. The TH350 was used till 1986 If Im not mistaken, meaning 1985 and 1986 would probably have TH350C before a TH400.

Also I recall a conversation about TH375's being used because the driveshaft could be kept the same as either outgoing th350 or maybe it put it at the same length as some of the manuals, or matched the 700r4. I dont remember.

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It also seems axle ratio was a big reason for MX1 (TH400)

but the "standard" trans for every single 1987 truck line was manual. evidently the 3 speed saginaw column shift never went away because 4.3l 3speed on the tree was the default v10 or r10 which ever is the 2wd.

 

[AuroraGirl]

Actually, they 100% did. The 3-speed auto was still the standard auto trans and the th350 was out of production at that point, so they got the th400.

Several members here have had the 4.3/th400 combo in stock form.

Two things I thought youd find interesting, roller cam 4.3 in 87 and the bright moldings went away in 87 for Scottsdale and silverado was discontinued. i seem to recall a question about locking strips or trim pieces on them

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[bucket]

I will never claim to know exactly what years GM put the th400 behind a 4.3 V6, all I know for sure is that they did at some point in the 80's.

 

[AuroraGirl]

I will never claim to know exactly what years GM put the th400 behind a 4.3 V6, all I know for sure is that they did at some point in the 80's.

And thats all that really matters here.. that it happened, and wasnt rare.
and his axle ratio OE being that 2.73 increases the odds if looking at that 87 data, but idk about 85. point is there is reason to look at his ratio, his driveline hes going to put in length vs maybe the one thats in it now, etc.

I wouldnt have commented if it was going to be such a problem

 

[Vbb199]

I guess I personally wasn't denying that a 4.3 could come in front of a th400, but as I said, the th400 would ear the entire 150 horsepower the 4.3 made just to rotate it hahahahahhahaa again, very exaggerated, but with a 2.48 first, that ol 4.3 would need a 3.73 or 4.10 to make it even lunge forward

 

[KCKKen]

Thanks everyone!

The two trucks I have are definitely unique to each other - the original 85 had a 305 with auto overdrive transmission, and the parts truck 85 had what they called the "vortec" V-6 in it with a "MX1" transmission option, which until I read through the posts seems to be a TH-400 (never could find a solid reference until now). This is the option sheet from the parts truck:

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The "G51" extra capacity rear was an unusual code to find as well.

Today I spent most of the day chopping up the fire-damaged cab from Project Calvin -- I located a really nice cab to replace the mess I was left with, so now I need to get ready to receive it at the house, strip it down and do a little repair to it - nothing like the old cab!

Thanks again for all the info -- I need to post an update to the project page, will try to do that this week.

Take Care,
KS