Short/Long Pinion Sterlings use differnt length driveshafts?

[bike-maker]

So here's my situation;

Some of you may remember a recent thread of mine that told the tale of the rear end in my truck going up in smoke (literally!)

So I sourced a new(er) long pinion Sterling 10.25 with limited slip out of a 94 as a replacement.

Tonight I went to bolt up the driveshaft, and it is now too long.

The truck originally had a 460/C6 with a BW1345 transfer case and Dana 61 rear end.

Then I swapped in a 7.3IDI/ZF5, and a short pinion Sterling 10.25" out of a 89; I kept the BW1345 for it's non slip yoke and to reuse the original driveshaft.

So I have 2 options; have my current driveshaft shortened, or go out and source a driveshaft out of a newer ZF5 truck. I like the idea of finding a newer driveshaft because it is a bigger diameter and uses bigger U-joints.

So if I go to find a newer driveshaft, is there a difference in length between the short pinion / long pinion rear ends?

 

[franklin2]

Your tolerances must have stacked up against you. There was a recent thread where a guy put a short pinion rearend in his later model truck, and was able to re-use his later driveshaft. But of course he just slid it out a little bit.

I don't know what the theory is on the different driveshafts. I was surprised when I did my zf swap, had a donor of the same year (89 to 89) and my c6 driveshaft was a different length(very small difference) but the zf shaft seemed twice as heavy when you picked it up, and it did use larger u-joints. I swapped my yoke from the donor so I could use the larger zf shaft.

If I understand you correctly, you do not like the slip joint transfer cases? I think they are great, they seem to last forever with no wear, unlike the fixed yoke shafts with the external slip yoke, where if you do not keep them greased on a regular basis, they wear very quickly and the plastic coating they put on the splines seems to not last very long.

 

[bike-maker]

There only appears to be about 1/2" of difference between the 2 rear ends, but it was just enough to bite me in the ass.

After searching the local Craigslist and car-part.com, there's a couple of the short pinion (87-92) driveshafts close to me, no dice on the long pinion version (93-97).

With the fixed yoke, if I ever broke the Ujoint directly behind the transfer case I could still unbolt the rear drive shaft and drive it home. At least that was my reasoning.

 

[bike-maker]

Just a little thinking out loud here;

With the truck sitting on jacks under the frame rails and the rear end hanging from the leaf springs (resulting in the rear axle sitting about 6" lower than ride height), the rear driveline still won't quite go short enough to fit into it's yoke.
And the difference between the short/long yoke rear ends is only about 1/2" as I measure it.
I'm starting to think my rear driveline might have been just a tad too long with the short pinion rear end, and that the extra weight of the 5er sitting on the rear axle combined with a too short drive shaft might just have led to the demise of the short pinion rear end.

 

[franklin2]

If that's the case, then it was putting a thrust load on the transfer case, and would have given a very rough ride(springs could not compress).

Have you ever shortened a shaft yourself or do you have a shop that would do it? You just have to grind the weld down on whichever end you chose, and drive the end out of the shaft. Cut the tube the required amount, and then drive the end back up in the shaft. Re-install the shaft in the truck, and mount a dial indicator somewhere on the truck body or frame, so it rubs the shaft near the end you cut. Rotate the shaft by hand measuring the run-out. Tap the shaft with a hammer till the run-out is as small as you can get it, then gently take the shaft out and weld the end back in, in little short spot welds on opposite sides, slowly filling it in all the way around.

 

[FORDF250HDXLT]

yeah im shocked to read you need a longer shaft.i measured the two and only came up with like a 1/4" difference.
sounds like your shaft was too short to start with if the latter sterling yoke is enough to give you troubles.

 

[bike-maker]

I'm going to crawl under it tomorrow to make sure.

And the driveshaft is now too long, not too short.

I did just recently grease the hell out of the slip yoke, so there's a chance there's enough grease that it won't compress it, but it does look to be pretty close to the end of it's travel. One can wish....

FWIW, my truck rides like a skateboard anyway, so it very possible could have been binding and I wouldn't necessarily notice the difference.

 

[PwrSmoke]

The couple of times I have seen a long pinion R&P/yoke installed, it did make the slip yoke compress a little more but there was plenty of movement left. I do think that the Sterling has a longer snout than a D61 and that could be your trouble. I suggest you get the wheels back on the ground (so you can measure at normal ride height... very important) and measure the distance between the t-case output flange and the axle yoke. See if you can get a measurement of one of those short pinion shafts (compressed, extended and median) and see how it compares to the one you have and the measurement you make (which should come out toward the extend side of median). I think there's a very good chance one of them will work. If you google "Tom Woods Custom Driveshafts" he has a very good PDF you can download on how to measure driveshafts.

I checked my data books for shaft lengths and that's one thing not listed, though they do talk about u-joints and driveshaft angles/pinion angles, etc.

 

[bike-maker]

So I slept on it and woke up the next day with a revelation;

I didn't have the shocks hooked up yet, and the rear axle was hanging from the truck, suspended by the leaf springs. I was stuck in the mindset that the rear axle moved straight up and down, with no forward and back movement. This was incorrect. Because the front of the leaf springs cannot move forward or backward, when the leaf springs flatten out (rear suspension is compressed), the axle actually moves to the rear of the truck. I bolted the shocks back on the truck (which limited the travel of the rear axle), and the drive shaft does indeed fit.
After studying the rear suspension and drive line angle, it actually appears that the length of the rear drive shaft just barely even changes during normal cycling of the rear suspension. Not what I was initially thinking.

I feel kinda stupid about it, but at least I learned a little more about how the rear suspension works.

 

[82F100SWB]

I had to shorten the rear shaft on my mud truck when I put long pinion gears on it, it was bottomed out at ride height, and that was when it was stock suspension wise. I had to take 2" out of the shaft to get it back to the middle of travel. I highly suggest measuring your yoke to yoke legnth with normal weight on the truck, and then adjusting driveshaft legnth so it is centered in the slip yoke travel.
The axle does move to the rear slightly, but that driveshaft will still compress and bottom out under suspension compression.