NEED HELP Oil slinging from universal joint between transmission and drive shaft on 2003 Sierra 2WD


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Hello all,

Here's observations, analysis, and a plan. Do you agree/disagree? What would you do differently?

2003 GMC Sierra 1500 SLE, 2WD.
Owner is a family member.
Miles are very low (49,800 in 17 years).
I have drained and refilled the transmission fluid a couple of times within the past 2 years. The level seems stable.


No drivability symptoms are noticed, other than an occasional hard shift "clunk."

Oil or grease has apparently slung from the U-joint at the front of the drive shaft, onto surfaces above and below it (see photo 1).

There's a big oily splotch at the transmission output shaft (tail shaft).

Also, the surface of the rear of the transmission body is oily, both above and below the pan seal.

By hand I can wiggle the front of the drive shaft back and forth, so much that the output shaft of the transmission wiggles back and forth barely visibly.

The seals on the U joint look ok: they are in place, not oily, and not dry-rotted.

Also, most of the surface of the differential case is oily (see photo 2). The rear U joint (at the rear of the drive shaft, entering the differential) looks dry, it does not wiggle, and its seals look fine.


I think the splotch of oil/grease at the transmission output shaft indicates that that seal is leaking.

The Chris Fix U-joint video at
mentions at 5:48-5:58 that vibrations from a bad U joint can damage the transmission output seal. I suspect that's what happened.

To explain the oily transmission body and differential case, I guess it's from oil droplets/mist that sling off the U joint and blow around under the truck, but I'm not sure.


Replace both U joints on the drive shaft. (I suspect the front one is bad, and might as well replace the rear one too.)
Replace transmission output seal and bushing. While the transmission extension housing is off, replace its seal too.*

*When replacing the output shaft seal, this video by DIYGarage bryangregorytv
"Tail shaft seal and bushing replacement"
says at 2:28-3:37 that it's good to also replace the bushing, which requires removing the tail shaft and extension housing. While the extension housing is off, replace its seal too (the seal on its front, against the rest of the transmission).

I don't think that this work will require draining or dropping the transmission pan. Can anyone confirm/deny that? (It's currently drained, to replace the transmission filter and gasket.)

I think DIY is possible, but because of the scope the owner prefers to use a trusted local shop.

How does this plan sound? Any suggestions?



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You will not have to R&R the Transmission Oil Pan... You just have to clear anything blocking access to all of the Tail Housing Bolts in order to get the thing out and over on your work bench where you can Kill 2 Birds with 1 Stone (R&R Rear Tail Housing Bushing and replace the Slip Yoke Seal)

If the Drive Shaft Slip Yoke might also be leaking Transmission Fluid as well through the End Plug... This Dude's suggestions for How to Diagnose and STOP that problem are VERY Smart:

... and for the R&R of a Rear Differential Pinion Seal:

Last edited:


When you pull the driveshaft and replace the u-joints, it's also a good idea to put some grease in the yoke splines before slipping it back in the tail shaft. This will prevent any clunking from there.

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