Why did some SWB trucks have a two-piece drive shaft and others not?

[got2haul]

My '80 stepside has a 2-piece driveshaft with a carrier bearing.  As I was looking over the 1980 SWB fleetside I just picked up I noticed that it has a 1-piece drive shaft, with no carrier bearing (obviously).  Does anyone know or have a theory as to why GM did this -- same year, same wheelbase, different driveline?

There are differences in the driveline: the stepside has the 4-speed granny-low transmission (what's the nomenclature for this transmission -- model name/number, gear ratios?) while the fleetside has an automatic.  Does this have anything to do with it?

[frogman68]

Cant help with the drive shafts but the tranny is a Muncie SM465

[gold84gmc]

i dont know why they did that...but i have an 84 gmc c2500 3/4ton long bed with a th400 automatic tranny and it has a 2 piece drive shaft

[smitty77]

My '79 has a two-piece driveshaft as well.  I heard they were standard on the "Big 10" and "Heavy Half" models, but I don't know if this is really true.

Smitty

[dumbucket1]

the majority of longbeds got 2 piece driveshafts but I have never seen a shortbed with one

[JRConnieK10]

Confusing, my longbed 1/2 ton 1-piece and I have an 83' shortbed 1-piece. Both are 4x4 if that makes the difference. And the longbed has manual sm465 the shortbed is auto. Both have 208 transfercases.

[Captkaos]

Does your Stepside have HD springs on it?  2 piece driveshafts were always put in HD trucks.  The SM465 leads me to believe it is a HD truck.

[frogman68]

Does your Stepside have HD springs on it?  2 piece driveshafts were always put in HD trucks.  The SM465 leads me to believe it is a HD truck.

Chris according to this site
http://www.novak-adapt.com/knowledge/sm465.htm

this tranny was used in light duty trucks. I trust your info more, what was more likely stock for a truck of that era ?

Btw dont play hero and try picking this tranny up by yourself if you want kids in the future

[Captkaos]

It was used in light duty trucks all the way up to HD trucks.  I was trying to say that our trucks have a HD package called Heavy Half in the early years and they generally had 2 piece driveshafts and 56" leafs.

[got2haul]

The RPO list that was in the glove box lists 1G50, "Heavy Duty Rear Springs."  So maybe that's it?

[Captkaos]

That is it...

[zieg85]

I had heard back in the day that GMC was always more HD than its counterpart.  I know that the GMC 1/2 ton had leafs where the Chevy 1/2 ton had coils back in 72.  Any truth to that?

[1976Scottsdale]

Not to steal the thread, but I just sold a 78 K-20 4x4 3/4 ton SM465/NP205 3.73 gear ff rear dana 44 front that had a 2 piece rear shaft.  It too was optioned heavy, also with a factory tach... funny thing, that somehow found its way to my storage shelf before the truck left.

[VileZambonie]

Two piece shafts allow for more clearance and reduced driveshaft diameter. One piece shafts, the longer they are the fatter they need to be. Is one better than the other? I'll let you know when I have one break into a million pieces.

[fitz]

 To add to the confusion My 87 V30 (k30 in my mind) had a factory 454 TBI, turbo 400/205, and a Dana 60/14 bolt (3.73's) with a 1 piece driveshaft. I would have thought all 1 tons got the 2 piece shaft.