'68 c10 4 speed to th400 swap, driveline question

[Greasey Harley]

I dropped a TH400 core off at the local trans shop for rebuild today. My core has a slip yolk. My truck has a 2 piece drive shaft. (2wd swb) The rebuilder wanted to know if I wanted to swap to a bolt on yolk. He says that bolt on yolk is correct for a 2 piece driveline.
Anybody know what configuration it would have come with in 68?
Any advantages to switching to a 1 piece drive line?
Should I just have a new front driveline made and use the bolt-on yolk?
I would like to keep the configuration as "stock" as possible.

[HO455]

As far as I know the bolt on yoke was a 4x4 item only. The bolt on yoke was at the transfer case output shaft.
Most 1/2 ton trucks (automatics with coil springs) with a 2 piece drive shaft have to have a sliding yoke. The sliding yoke is where the length adjustment occurs as the suspension moves up and down causing the driveline to move fore and aft. A bolt on yoke would not slide in and out. The carrier bearing is mounted in a large rubber bushing that allows the bearing to move fore and aft with the driveline.
On 2 wheel drive leaf spring trucks and 3/4 ton coil spring trucks with 2 piece drivelines have a splined sliding joint in the rear driveline. On those trucks the carrier bearing is fixed not rubber mounted. The fixed bearing means the front driveline does not move fore and aft. Thus the splined sliding joint is where the fore and aft movement is absorbed.
If your truck is not lowered a lot you should have no problem running the stock 2 piece set up. If it is lowered a fair amount you might benefit from a different drive shaft configuration.
The advantages of one piece driveline is cost. But if you convert to a yoke style the cost will go up as the drive shaft will have a sliding joint built into it.
In addition not all Th400 output shafts are drilled and tapped for a bolt on yoke.

[Greasey Harley]

The front driveline is solid, the rear driveline has a slip yolk after the carrier bearing.
Front shaft (no slip yolk)

Rear shaft (has slip yolk)

[Accelo]

Stay with the slip yolk which would be stock on a two wheel drive.

Your drive-line may a two piece shaft but that doesn't mandate it has the slip yolk built into it. I am confident your transmission re-builder knows this just a it's likely a communication issue?
Rick

[Greasey Harley]

Originally Posted by Accelo

Stay with the slip yolk which would be stock on a two wheel drive.

Your drive-line may a two piece shaft but that doesn't mandate it has the slip yolk built into it... Rick

...but my drive shaft does have a slip yolk on the rear section. what would be the advantage of a slip yolk on the front shaft?
Were SWB AT trucks 1 piece driveline or 2 piece?
Did trucks with 2 piece drive lines have slip yolks on the front shaft as well as the rear?

[Accelo]

I just took apart a 70 with a 3 speed transmission. It had a slip joint at the transmission and was a two piece drive-line. This was a factory short box.

All PowerGlides and THM 350's automatics were set up to slip at the transmission. Only the THM 400's had the optional, bolted in place, yolk.
The bolted on yolk setup was more typical in the 3/4T and up trucks and motor-homes. Your truck is a 4 speed. No slip yolks on the granny transmission in 2 wheel or 4 wheel drive.
Ok, I just reread your post. You have a 4 wheel drive. This slip yolk in the middle of the drive-line is likely stock on the 4x4. So leave it that way and use what the re-builder recommended (the bolt on yolk)

"what would be the advantage of a slip yolk on the front shaft"

I have never observed a front drive shaft with out some slip yolk in it somewhere. (*Unless the differential isn't floating) As the axle goes up and down the drive shaft has to lengthen and shorten.

[HO455]

Originally Posted by Greasey Harley

...but my drive shaft does have a slip yolk on the rear section. what would be the advantage of a slip yolk on the front shaft?
Were SWB AT trucks 1 piece driveline or 2 piece?
Did trucks with 2 piece drive lines have slip yolks on the front shaft as well as the rear?

I can't tell you why GM didn't put any slip joints between the transmission and the carrier bearing, my guess is there must be a downside side to that.
Only one point of length adjustment is needed for our trucks.
The photos are of the stock driveline from my 67 C10 Burban that was a Th400 from the factory. It has no slip joints, the rubber mounted carrier bearing, ad the long Th400 yoke. Typical 1/2 ton coil spring long bed automatic truck stuff.