U joint difference 7-1/4 and 8 3/4

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Mopar92

Mopar92

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Installing an 8 3/4 and its replacing the 7 1/4. I believe I've been told 2" is how much I'll need to shorten the drive shaft. My question is this... What U joint # does an 8 3/4 use? If the driveshaft shop reuses the shaft yoke, does that need to be changed? I just don't remember what U joints the 7 1/4 vs 8 3/4 are. Thanks guys.
 
My 8 3/4 has the yoke to use the conversion joint. I believe it's 7260 at the shaft, to 7290 at the yoke. Kinda socks cause you can't get a "greaseless" joint.
 
Yeah. I just found some more info after 30
Min of search.... There are a few different u joints for the 8 3/4 alone!
 
Recently I read a thread on shortening the driveshaft when installing an 8.75" rear end. After I finished I also wondered about the difference in yokes. So this was the perfect question I was going to ask. So I also did some searching to figure out what a 7260 and 7290 was. So if you do have a 7260 at the shaft and 7290 at the rear-end yoke, there is a one-piece solution in a conversion U-joint for $40 (on eBay).

http://www.ebay.com/itm/New-Moog-72...ash=item3cfd86d1d3:g:OosAAOSw1-RUam1c&vxp=mtr

However, you do need to verify the sizes you have on both ends.

Thank you Mopar92 for asking this question.

**After more research, same part available at Summit for $26.
 
Is there a chart? I'll throw some calipers on them to measure what 8 3/4 yoke I have. I wonder if the drive shaft shop would even reuse the shaft yoke. They might put a new generic one on. If that's the case, I should make them match. Good info. Thanks guys.
 
Hey Mopar92,

You do ask good questions. I also wondered if the old shaft yoke would be reused.

Look on the bottom of the eBay link. There is a chart that gives dimensions of both the 7260 and 7290.
 
g413 said:
Hey Mopar92,

You do ask good questions. I also wondered if the old shaft yoke would be reused.

Look on the bottom of the eBay link. There is a chart that gives dimensions of both the 7260 and 7290.
Click to expand...

Right on. Thanks.
 
Mopar92,
I just had my driveshaft cut and balanced (yesterday). The shop did not install a different yoke, they simply cut the shaft, rewelded, and rebalanced. I have the 727 trans with a 8-3/4" rear with a 489 carrier. I used these u-joints: GMB2111306 from rockauto, they have a 1.078" bearing cap diameter.
 
The chart says 2.28 or 2.26" But I took my car on the trailer to shop and had them measure what they needed- with weight on wheels/tires- not on jack stands they made a new tube and all
 
Most all driveshaft shortening companies use your original yoke and just shorten the shaft and weld the time back on!! They can't guess what U joint you will be running, they just assume you'll be running what you brung em!!!
 
An 8 3/4 can use the same U joint as the 7 1/4 or it can use the larger U joint. Measure the length of the yokes along the centerline of the bearing cups. There is a conversion joint to mate to the larger yoke and use your driveshaft, if that is what you have.
 
What are the condition of your leaf springs for ride height? Are they still bowed and the height you like, or are they sagging and almost flat? Your driveshaft length should be measured weight on wheels to your combination, not what you've just been told. If you have your driveshaft shortened now, and replace your leaf springs later on with different ones that could be a different height, it could throw the required length of your driveshaft off. Measure twice, cut once. Good luck
 
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