I sent an email to Dennys with questions about my U-joint. Here is what I got in return.

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QUESTION
I have a 3" OD aluminum driveshaft and the U-joint provided was a 1350 style I believe. It did not fit in my differential yoke. I had to research a “Precision” brand U-joint to get me going. The model was 447. I drive a 6000lb SUV and make around 650rwhp so I don’t think this will do the job. I am looking for the strongest U-joint in the size below: (according to your diagram)
A:92.97mm/3.660in
B:92.74mm/3.651in
C:28.58mm/1.125in
D:30.20mm/1.188in
The end caps on the small sides say E40 and the large sides say E50 if that is of any use. My phone is xxx-xxx-xxxx. Please call with questions. Chris

ANSWER
The 3 inch Aluminum should never be used in a 6000 pound SUV with 650 rwhp. It should be at least a 3.5 inch if it is a short length and a 4 inch or a 5 inch for a longer application. It should be 1350 series throughout and no combination u-joints should ever be used.

Tech dept
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It makes me wonder, what size DS's are you guys running? I thought 3" aluminum was pretty stout. The pinion yoke was too small to accept the 1350 joint that came with my DS. That's why I went and bought the Precision brand. It has been working fine for 2 years or so.
I paid pretty good money for this DS and don't want to buy another because I doubt I can find a buyer for mine as it was a custom measurement for my 80E in a Tahoe.
What should I do?

 

Ok, I just went to bouble check and the DS is acually 3.5" OD aluminum. Maybe I just remembered wrong. Even still I would consider this DS to be pretty long since it is a one piece at 50" from weld to weld.

 

I went with a 3 1/2" steel shaft because of the strength and smaller diameter for putting a driveshaft loop around it for trips to the track,mine is 67" long and has 1350 u-joints also,but I had to swap to a 1350 differential yoke in order for it to fit,if you need a part # I have it somewhwere!

 

Heck yes I'd like that part number!

 

Mine is right around 70" and I used a 4" for a while and went to a 5" when I did my 80e swap. The stock one was 4"

 

Well I wonder why the DS place told me 3.5" was fine. They knew what it was going into. Judging from the last 2 posts my 50" is not really that long. Maybe I will be fine just upgrading the pinion yoke to a 1350. I'm not looking for high speed runs. I rarley break 100mph.

 

I think Denny's sells the yoke you need, it was years ago but i think I got my billet 1350 yoke from them.

 

It would appear you are right good sir...
http://www.dennysdriveshaft.com/p121...6_10_bolt.html

 

part# is spicer 3-4-8681-1,hope this helps,unless you already found it!

 

Thanks everyone. Got it ordered.

Now how do I calculate the tq for the pinion nut? Backlash and all that jazz. Is there a cheater way like on my GTO? Hand tight then another half turn?