TH400 behind a 350 OEM, when and why?

[davepl]

The TH350 was introduced for the 1969 model year as a replacement for, but sold beside, the Powerglide.

Before that you got the glide or the 400. Before 1969 it had to be one or the other for an automatic, barring odd bird truck transmissions I'm not up to speed on.

[Eddie H.]

My 69 was born with a 307 and TH400.

[factorystock]

Originally Posted by leftybass209

I ask because i'm going to look at a truck tomorrow that says it has a Th400 behind a 350, and is claimed to be stock; totally possible I understand. I'm interested in WHY this would have been ordered that way, and in what circumstances, if any, it may have been suggested by Chevrolet as a better fit.

This thread is getting to a point where we need to be year and model specific. 1969 was the first year for the TH 350 and 1966 was the first year for the TH400 in pickups. These years are approximate, we really don't know the exact dates these transmissions were available for production. From '66-'68 ( early build '69's ? ) The TH 400 was the only 3 speed automatic in pickups. So, IMO, the question needs to zero in on later build '69's as well as all '70 '71 and '72 C 10- C20 non big block trucks. Anybody have a factory installed TH400 in these specific model trucks? It appears all C 30's with ordered with automatics came with the TH400 regardless of engine.

[leftybass209]

Originally Posted by factorystock

This thread is getting to a point where we need to be year and model specific. 1969 was the first year for the TH 350 and 1966 was the first year for the TH400 in pickups. These years are approximate, we really don't know the exact dates these transmissions were available for production. From '66-'68 ( early build '69's ? ) The TH 400 was the only 3 speed automatic in pickups. So, IMO, the question needs to zero in on later build '69's as well as all '70 '71 and '72 C 10- C20 non big block trucks. Anybody have a factory installed TH400 in these specific model trucks? It appears all C 30's with ordered with automatics came with the TH400 regardless of engine.

I think my questions were answered awhile ago, and year doesn't play a factor in it. The why and when was answered with there being no definitive options ordered on a truck that mandated the need for a TH400, versus a powerglide, or TH350.

Also, through more research I found that through all the original literature and brochures that I could find, there is no statements made that a TH400 was a heavy duty automatic when compared to the TH350. In fact, I haven't yet found any references to a numerical designation, the transmissions are simply generically referenced as turbo-hydramatics in print. Of course, this is all based on research done so far, but for all intents and purposes the answer has been found!

Thanks everyone! I'll post some other information (solely opinion and observation) based on an interesting brochure I found.

[RedRoad]

This is the only reference I can think of that lists the T400 specifically with recommendations for use.

[GTSideSwipe]

Yeah I'm not really sure.. Me and my uncle both have C20s both having the original engines and transmissions. The only difference is mine is a 69 with a 350 and TH400 and his is a 71 with a 350 and a TH350 behind it...

[mmiddle]

My 69 C/10 was a factory 350-2bbl./TH400 low hump Plane-Jane w/factory air. Sold it years ago, but the SPID did say Turbo Hydro-Matic and HD rear springs Cant remember the codes.

[GTSideSwipe]

Was able to take a picture of my SPID and the rear end overloads. Stock 69 C20 with a 350/TH400 with a small hump and it has overload leafs with coils. It also has a 12 bolt 4.10:1 rear end axle.

:Update:

Got a little better photo of the SPID.

[stepbox]

Hello,

I'm new to this forum and this subject is very interesting to me.
I have a 69 step side I'm building,using a 350 engine. This is going to be a daily
driver,but I may want to tow a trailer (camper or small car hauler) which is the better trany to use the 350 or the 400.
I hope it's ok to high jack this thread.

[GTSideSwipe]

Originally Posted by stepbox

Hello,

I'm new to this forum and this subject is very interesting to me.
I have a 69 step side I'm building,using a 350 engine. This is going to be a daily
driver,but I may want to tow a trailer (camper or small car hauler) which is the better trany to use the 350 or the 400.
I hope it's ok to high jack this thread.

The 400 would be the better one IMO. The 400 takes more power to spin though.

Gear ratios: (Lower is best for MPG)
350 - 2.52 1.52 1.00
400 - 2.48 1.48 1.00

If you're looking for MPG then 350 but for towing I'd go for the 400 because from what I've read the 400 lasts longer and can take more abuse.

[stepbox]

Thanks GT,I will be asking more questions in the future.Right now I'm in the take down stage

[kwmech]

I have a '72 that I will be piecing out..3/4 ton, leaf spring, camper special dual tanks etc. with a 350/350 combo. You would think being a camper special it would have a th400.

[Gimme Jimmy]

GM built plenty of trucks with the T400 trans behind 350 engines from the factory. You can identify the trans by the shape of the pan (look up under the truck) the T350 oil pan is more or less square with a small "jog" in one corner at the rear. The 400 pan is oddly shaped and longer, with a somewhat "pointed" extension at the rear of the pan.The 400 is a very strong trans. the 400 kickdown is electric, with a switch on the carb linkage on models up to 1970. On the '71 and '72 it is mounted under the gas pedal. The T350 kickdown is cable operated. The T350 is quite strong but geared slightly lower (in 1st and 2nd) than the T400. The T350 in stock form, is prone to breakage of the output shaft. (there are more durable aftermarket shafts available). The T400 is the "Big Boy" trans and is extremely durable. The 400 was probably one of the strongest auto transmissions of it's day, rivaling the Ford C6 and the Dodge 727B.

[Gimme Jimmy]

GM built plenty of trucks with the T400 trans behind 350 engines from the factory. You can identify the trans by the shape of the pan (look under the truck) the T350 oil pan is more or less square with a small "jog" in one corner at the rear. The 400 pan is oddly shaped and longer, with a somewhat "pointed" extension at the rear of the pan.The 400 kickdown is electric, with a switch on the carb linkage on models up to 1970. on the '71 and '72 it is mounted under the gas pedal. The T350 is geared slightly lower (in 1st and 2nd) than the T400, but the T350 is in stock form, is prone to breakage of the output shaft. (there are more durable aftermarket shafts available). The T400 is the "Big Boy" trans and is extremely durable. The 400 was probably one of the strongest auto transmissions of it's day, rivaling the Ford C6 and the Dodge 727B.

[clinebarger]

Originally Posted by Gimme Jimmy

The T350 in stock form, is prone to breakage of the output shaft. (there are more durable aftermarket shafts available).

You must be talking about the Input Shaft, Even then you have to be north of 500 ft lbs to be in danger of breaking one, The Intermediate Sprag Race is the weakest part in a stock TH350.

I have never seen a TH350 in a '69 truck (That had Turbo Hydramatic in the SPID), I believe the TH350 was not available 'til the '70 year model in trucks.

[Gimme Jimmy]

TH 350's DO break output shafts. I have a buddy who had one in a '65 Malibu that broke under normal use. I have heard of some breaking in 2wd trucks as well.
As far as I can tell GM installed any trans it had in stock on any given day. I personally owned a '68 Chevy half ton with a 307, coil rear and a T400. I have a friend with a '72 4wd half ton with a 350 engine and a T350. There is such a thing as a '69 3/4 ton with a 292 six cyl. and a T400. It came that way from the factory. The only way to tell what you have is to get under the truck and look at the trans pan.

[clinebarger]

Originally Posted by Gimme Jimmy

TH 350's DO break output shafts. I have a buddy who had one in a '65 Malibu that broke under normal use. I have heard of some breaking in 2wd trucks as well.

You saw, With your own eyes, A broken TH350 Output Shaft?

[88Stanger]

mine is a 1969 c-10 with a 350ci and turbo 400, all stock from factory, with the build sheet to prove.

[special-K]

Originally Posted by factorystock

This thread is getting to a point where we need to be year and model specific. 1969 was the first year for the TH 350 and 1966 was the first year for the TH400 in pickups. These years are approximate, we really don't know the exact dates these transmissions were available for production. From '66-'68 ( early build '69's ? ) The TH 400 was the only 3 speed automatic in pickups. So, IMO, the question needs to zero in on later build '69's as well as all '70 '71 and '72 C 10- C20 non big block trucks. Anybody have a factory installed TH400 in these specific model trucks? It appears all C 30's with ordered with automatics came with the TH400 regardless of engine.

Good point. And we still have people posting about their '69 and earlier trucks coming with TH400. THEY ALL DID, if they got RPO M49. The thread needs to adjust to discussing the years that offered both TH350 and TH400 since the topic of this thread is what it took for a truck to get a 350/TH400 combo. The fact that the SPID doesn't differentiate and brochures don't play up the differences shows it wasn't a matter of marketing, just the mfgr's spec for HD applications. Also, the fact that all C/30s got TH400 automatics is proof in that pudding. In fact, at first a TH400 in a C/30 came with no 'Park' position. What year was the TH400 first put in C/30s? Was it from the start, or once the TH350 came out? I have had a '70 C/30 with no 'Park'.
Still looking for the rhyme or reason for the TH400 behind a 350 in 70-72.

[mmiddle]

^^^ If these dates are correct for the TH400 in '66 and the TH350 in '69. Then 1969 was the first year you could get a 350/TH400 combo. 1969 was the first year for the 350.
I would imagine the TH350 was first earmarked for cars as the PG was phased out at the same time. So, this might mean that a true 350/TH350 combo in a '69 truck could be a rare find.