Driveshaft Difference for 14b SF and 14b FF

[HotRodPC]

Here's a question I've never had to consider before so I don't know. Maybe some other gearhead may know.

On my 88 Burb that I want to sell as a roller, it currently has a 14B Full Floater with 3.73 gears that I'd like to keep. I've got 2 14 bolt Semi Floats with 4.10 gears in my other 84 & 85 C20's that are going to be consolidated.

So I am thinking I'd like to swap one of the 14 bolt Semi Float 4.10 axles into the Burb before I sell it and keep the 14B Full Float for my K10/1500 axle conversions.

I know the spring perches and all will be the same and it should bolt right in.
Question is, What about dirveshaft lenght??? Is the 14b SF shorter or longer than the 14b FF that would require me to have the driveshaft altered??? Would it need to be shorter or longer??? Anyone know the amount of difference if different???

 

[crazy4offroad]

14b sf are usually 1310 or 3R. 1350 yokes are available as an upgrade from places like Denny's Driveline for around $70. The 1310 is 3.219" wide from the end of the u-joint cup to the end of the other cup (almost 3-1/4"). The 14b ff takes the 1350 which is 3.625" (3-5/8") so there should be 1/2" difference there, IF the 14b sf has the 1310 and not the 3R. 3R is an internal c-clip style and has 1.125" (1-1/8") caps, where the 1310 has 1.0625" (1-1/16") cap.

I thought the 14b ff would be bigger than the 12 bolt I replaced, in relation to the centerline of the axle shafts to the u-joint mounting spots of the pinion yoke but actually it is a little shorter. This may be something you may want to check, which can be done pretty easily with a carpenter square and a tape measure.

 

[HotRodPC]

I didn't even think about the U joint size. I am concerned about the driveshaft length first. But, doesn't sound like its feasible. Maybe I'd be better off putting the 3.21 ratio out of my 84C20 DD in the burb and the 3.73 in the DD until I retire it. I want the 3.73 for axle upgrade in the 85K1500. It has 3.73 gears now. Pops has a 10 bolt 3.73 to go with it, or I could just change to 8 lug front hubs and run the 3.73 14b FF.

 

[RetroC10Sport]

The interchange is saying there is a difference between the 350 and 454 (two piece, this is rear piece, front is the same 1973-90.) but no difference between full and semi (both were available in 1988).

 

[crazy4offroad]

The interchange is saying there is a difference between the 350 and 454 (two piece, this is rear piece, front is the same 1973-90.) but no difference between full and semi (both were available in 1988).

Post up this interchange thingy so I can bookmark it, if it's a website. I'm in a driveline nightmare myself!

 

[RetroC10Sport]

It's a program, same one the junkyards use.

 

[HotRodPC]

The interchange is saying there is a difference between the 350 and 454 (two piece, this is rear piece, front is the same 1973-90.) but no difference between full and semi (both were available in 1988).

So then if I understand right, you're saying the length is obviously the same between SF and FF. The difference between 350 and 454 is likely the U joint size I'd imagine. Cuz motor size isn't going to change the location of the rear axle, and if the front piece is the same all the way thru 73-90, that would tell me U joint size would be different based on motor size.

Thanks for looking that up. I really need to get in gear and play with that software.

 

[HotRodPC]

Its not U Joint size. I just checked. U Joint would be the same no matter the motor size, so maybe its the tube diameter is the difference for 350 vs 454.

 

[crazy4offroad]

Might have more to do with the 1/2 ton compared to 3/4 - 1 ton part of it. My 1/2 ton d-shaft has 1310 u-joints. Of course you throw in 2WD automatic slip-yoke vs 4WD slip-shaft and you get another issue to contend with.

 

[crazy4offroad]

It's a program, same one the junkyards use.

Wouldn't happen to have a link to it would you? Is it freeware?

 

[RetroC10Sport]

Ah no, it's super expensive. Because of owning a yard at one time, I still have my copy.

 

[crazy4offroad]

Aight then, luck-dawg lol.

 

[Sasquatch]

When i replaced my 14sf with a 14ff the driveshaft was the same exact size, so was the u-joint.

Before i did the swap i was told that the spring perches would line up.

Well they didn`t line up at all, not even close. I had to buy new perches and weld them on and i`m pretty sure that the shock mounts didn`t line up either and i had to weld on new mounts for them too.

The ff was from an 87 1 ton 4x4 and it went in my 85 3/4 ton 4x4.

I would measure before you`re left in the same crappy situation i was.

 

[crazy4offroad]

1-ton 14bolt ff's have 40-1/2" spring perches (to the centerbolt hole) and 3/4 ton 14bolt ff's have 42-1/2" spring perches. Which means the frames are a little more narrow, which would also offset the shock mounts an inch or so.

 

[HotRodPC]

Yep, Sas got stung by the 3/4 -1 ton difference. But that is awesome to know the 14B sf and ff use the same dshaft length and driveshaft. But that just makes me sick to know now that I could have swapped the 14b SF out of the pick up into that Burb before I sold it and kept the 3.73 14b FF. Damn !!! Oh well. I'll live. But now, I know, I won't be tossing out the 14b SF rear ends.