Need new UJs for a '79 K10, but confused what driveshafts I've got

[English]

I need new UJs, but I'm confused about what driveshafts I've got.
I think I've got a two piece rear driveshaft (three UJs between tx-box and rear diff), but according to the parts catalogue I should have a one piece. Am I misunderstanding?

It's the rearmost two that I need, just want to make sure I order the right parts.

On the drawing it's part 6 I don't get. 78-81, "B", one piece rear driveshaft. But mine's two piece, isn't it?

[Irish_Alley]

the catalog is saying you could have either or (or) someone could have swapped it at one point in the trucks life. but if you count 3 u-joints there should also be a #7 (carrier bearing) also. best bet is to remove the joint if you can and take that to the parts store that way you know youre getting the right part

[JohnnyPopper]

That is a strange looking rear drive shaft!

Can you show a pic of the UJ coming off the transfer case?

You did say it was 4x4, right?

[English]

the catalog is saying you could have either or (or) someone could have swapped it at one point in the trucks life. but if you count 3 u-joints there should also be a #7 (carrier bearing) also. best bet is to remove the joint if you can and take that to the parts store that way you know youre getting the right part

Oh I thought the catalogue was saying I should have a one-piece (as it's a '79).
Yes there the carrier bearing is there too.
I'm in the UK so these parts aren't on the shelf here unfortunately...
Yeah I've hardly got any info about the truck's history before it got here, so perhaps something's been changed. Maybe because it's lifted?

[English]

That is a strange looking rear drive shaft!

Can you show a pic of the UJ coming off the transfer case?

You did say it was 4x4, right?

Yes it's 4x4, long bed.
I'll take a better picture later

[JohnnyPopper]

The rear output of the transfer case should have a yoke that is locked on by a nut.

From there the UJ is connected to another yoke that has a spline that slips over the front of the drive shaft itself.

The rear UJ is what you see in your picture, down at the axle.

That would be considered a single drive shaft.

Your pic is strange because it shows the spline shaft reverse of what I just wrote, so there must be more to the picture that would explain it.

[English]

Here's a better photo, shows the whole lot.
To my understanding this is a two piece driveshaft, a one piece driveshaft would be one driveshaft between the transfer box and diff. Is that right or am I misunderstanding?

[Irish_Alley]

100% right

[JohnnyPopper]

Mystery solved! Is it a 1/2 ton?

I think someone changed it out when it was lifted.

[Irish_Alley]

sure. i think the main reason for the two piece was due to theres a physical limit on how long a driveshaft can be. the longer it is the thicker the walls have to be then the thicker diameter it has to be.

[English]

aha, so has it been changed? No wonder I'm getting confused!

Yeah it's a 1/2 ton

[Irish_Alley]

i dont think theres any real way to tell.

[JohnnyPopper]

English,

If your budget can allow, you should change all the UJ while you have it apart.

Also, check the spline yoke for excessive play, and clean it up.

If it's tight, lube it up good. When they wear, they vibrate at high speed.

Finally, check the carrier bearing for smooth rotation without chatter. If it's bad, that should be an off the shelf item.

[English]

Okay cool. Think my best bet is to take the UJs out and measure them, and order replacements that way.

Thanks a lot for all your help!