TH350 vs. TH400

['68OrangeSunshine]

What's an ''I-1500'' ?

[factorystock]

I 1500 is the series indentification for a '64-'66 GMC 3/4 ton with a straight six engine. 1500 is the 3/4 ton with the V6. '67 was the first year for the Th400 in the 1/2 ton Chevy 10 series.

['68OrangeSunshine]

Originally Posted by factorystock

I 1500 is the series indentification for a '64-'66 GMC 3/4 ton with a straight six engine. 1500 is the 3/4 ton with the V6. '67 was the first year for the Th400 in the 1/2 ton Chevy 10 series.

Thought it might be, but Chevy used the initial, L6, for inLine sixes, while Ford and Toyota called them I6s. M was the designator for GMC's V6s.
More recently Chevy has called them I6s, but I prefer the old ways.
Also I thought 1500 was 1/2 ton, 2500 = 3/4 ton, 3500 = 1 ton, etc. in GMC nomenclature?

[factorystock]

Originally Posted by '68OrangeSunshine

Also I thought 1500 was 1/2 ton, 2500 = 3/4 ton, 3500 = 1 ton, etc. in GMC nomenclature?

We need to be year specific when dealing with so many year model pickups. Your nomenclature was true for 1967 thru 1972 but in the during 1960 thru 1966 it was 1000= 1/2 ton, 1500=3/4 ton, 2500= 1 ton.As Bob pointed out, TH400 not listed in early '66 literature, but is listed in later in the model year literature.

['68OrangeSunshine]

OK. I learned something.
Having owned a '68 for 49 years, I have not paid attention to earlier vintages, much.
A C/1000 = C/10, 1500 = 20, 2500 = 30.
Never was mathematically parallel.
GMC Canada had 910 for 1/2 tons.
And my '71 GMC Jimmy is a K/1500, not a K/750. But a full size Blazer is a K/5.
Marketing numerology.

[Bob B.]

Originally Posted by factorystock

I believe your right Bob. The transmission wasn't quite ready when the first '66 pickups became available for sale in Sept. '65. By January '66, the Th400 was beginning to be installed on C20's and C 30's but not C 10's. The GMC literature shows it available on 1500 series which is equivilent to C 20 series.

Thanks for that.

[53burb]

interesting that they referred to the El Camino as a pickup in the earlier pic....aren't El Caminos based on the Chevelle/Malibu platform??
Sorry...didn't know how to copy/paste....but it's in post #27

['68OrangeSunshine]

Originally Posted by 53burb

interesting that they referred to the El Camino as a pickup in the earlier pic....aren't El Caminos based on the Chevelle/Malibu platform??
Sorry...didn't know how to copy/paste....but it's in post #27

Yeah, that's an old debate -- Car or Truck?
Personally, I don't care. I don't have one, so I've got no dog in that fight.
Yes, I believe they were on Malibu/Chevelle chassis [pl]. The GMCs were Sprints.

And if Pontiac made any, they'd be ,,El Cabron'' [The Goat.]

[BigBird05]

Bahhhhhh!

[mrein3]

Originally Posted by Bob B.

I have always wondered why in 1971 when automatic transmissions became available in 1/2 and 3/4 ton 4X4's GM used the TH350 only. The TH400 had been an option since mid-'66 in 1/2 and 3/4 4X2's but it wasn't until many years later it was used in 4X4's. Must have been a reason...

Bringing 'er all the way back to the original question in this thread, let me guess...

ALL manual transmissions offered with a NP-205 transfer case have/had a 10 spline output shaft.

The Turbo 350 has a 28 spline output shaft.

The turbo 400 has a 32 spline output shaft.

Maybe its as simple as New Process didn't offer a 32 spline input shafted 205 transfer case until later in the 70's, after the production run of this vintage was done.

I let a buddy's son store a '72 mutt in my yard for a few months. I sneaked a peek under it and noticed a th400/NP205 combo and very factory looking driveshafts.

I know for a fact that when swapping ANY '67-'72 factory offered tranny/transfer combo when coupled to a 205 for another factory offered 205 combo, it is a plug and play operation. The length difference and mounting to the crossmember difference is handled in the tranny to x-fer adapter. It sure looked to me like the th400/NP205 combo I looked at continued that tradition of making the swap plug and play for us guys 50 years later.

[factorystock]

Originally Posted by mrein3

Maybe its as simple as New Process didn't offer a 32 spline input shafted 205 transfer case until later in the 70's,

If GM wanted a 32 spline 205 made, New Process would have made it pronto! This was an era ( early 70's) when GM pretty much decided it would use their heavy duty automatic behind big blocks and 1 tons and use their medium duty automatic behind everything else. Around '72, they discontinued the 2 speed powerglide, so all automatics were listed as turbo hydramatics in literature.

[factorystock]

Special k put it this way, "coulda or shoulda" . Could be a topic for a completely new thread. Why not give the customer the option? During '69-'70, TH350 and TH400 automatics had different option codes( M38 and M49) '71 and later, one option code M49 for both autos. GM coulda or shoulda listed what 3 speed auto trans you had on the SPID without looking under the vehicle.

[70cst]

Interesting thread

[BLAZERMAN]

I had a 70 GMC 3500 that had a TH475 in it. I never could figure out the reason for it, it was a really odd truck.

[Caddylackn]

Originally Posted by BLAZERMAN

I had a 70 GMC 3500 that had a TH475 in it. I never could figure out the reason for it, it was a really odd truck.

Did the TH475 have the tailshaft mounted parking brake?

Being a 3500 and loaded, it should have one if you wanted to hold on a hill with an automatic. Motorhomes use the TH475 for that reason.

[BLAZERMAN]

Originally Posted by Caddylackn

Did the TH475 have the tailshaft mounted parking brake?

Being a 3500 and loaded, it should have one if you wanted to hold on a hill with an automatic. Motorhomes use the TH475 for that reason.

No it didn't have the drum drive line brake which I thought was off especially when this one didn't have Park. I used a 475 in my old 69 4x4 and it had Park and had the drum brake originaly. I have 2 tucked away for future.projects, one from a 34 foot Monarch motor home and another from a Cummins powered bread truck.

[Bigdav160]

The TH350 was first offered in the Camaro and Blazer.

What other GM bodies offered it the first year? My guess would be that the Hyramatic factory probably didn't have the capacity the first year to install it across the whole product line. Therefore, trucks being used more for work, stayed with the TH400 until 1970.

edit: Corvettes stayed with the TH400 as the only automatic choice until 1975

[Bob B.]

The 475 was sometimes called the 'AT 475 Easimatic' for some reason when used in medium duty trucks like the C-50/5000. Most didn't have a 'park' in them as a loaded truck could break the parking pawl on a hill, that's the reason for the output shaft drum brake.

BTW, the Turbo 350 was developed out of a 3 speed Powerglide project that didn't go anywhere. Ended up being an all new transmission.

[kwmech]

My 69 C30 GMC (originally a Class B motorhome) came with a 350 and a T400 (no park) and small hump with an HO72. All been changed out now