I need to replace the pinion seal on my '72 Supreme. I have a 10 bolt posi and want to make sure GM part #404294 is correct.

 

Hi Dave - Changing the pinion seal isn't something I routinely perform. I've replaced several on various pieces of equipment over the years - rear-ends in a variety of implements/vehicles. The part number called out in the GM Oldsmobile Chassis & Parts Catalog 1975 (June, 1975 Revision) is 404294. When you pull the pinion yoke check the short pinion yoke shaft carefully to ensure you don't see a damaged heavily scorched/worn groove on the yoke shaft which can be a place where oil can/will/might leak. If so, consider replacing the yoke. Good luck!

 

I need to do the same. Let us know how you handle the crush sleeve preload? If applicable. Thanks,

 

(1) The VERY first thing to do is completely clean the pinion yoke, the pinion seal area, and preferably the entire differential before you even think about performing a replacement & removing any hardware. Nice and clean.
(2) Next (important part) take some white finger nail polish (or similar) and create/mark a solid horizontal line on the pinion yoke directly across onto the pinion yoke nut through to the differential housing. You'll have a solid reference for reassembly.

 

2043 Timkin part number

 

Got it Norm. While I'm at it, I may as well replace the U joints and the rear transmission seal. Is there a recommendation for a solid, good quality replacement U joint, and are the front and rear the same? Also, what's the difficulty level on replacing the U joints, and what are the odds of the pinion yoke being scored?

 

Dave - I haven't changed U-Joints on a 1972 CS. Level of difficulty is probably ~5 on a scale of 1-to-10. Not that tough. I've changed more U-Joints in Ford trucks than other vehicles. Odds of a scored pinion yoke shaft? Don't worry about it until you remove it & examine it. R&R of the seal is most likely going to address your leaking issue. I mentioned it because "if" you find leaking again after you change the seal, you'll have a better notion where oil may be leaking if a seal R&R didn't stop the leaking. I don't know if your seal has ever been replaced or if it's original. I can't tell how much leaking you have from my arm chair. Unless it's "significant" a small leak isn't worth worrying about. After you have it out is the time to have this discussion. Odds will certainly increase w/ more aggressive driving, seriously launching numerous hole shots, countless airborne launches over railroad tracks & street curbs.

 

U-joints are relatively easy to replace, especially if you have a press. Most auto parts stores will loan a ball joint press that works exceptionally well for removing and replacing u-joints. Just use the C arm and the screw ram to press the old caps out and the new ones in.

 

Dave - If you don't already own this tool, consider purchasing it. Weekend mechanics don't need to purchase professional mechanic tools. These routinely sell for ~$35 and you'll find they more than pay for themselves - ball joints, bushings, U-Joints, presses in general. A good addition to your arsenal chest.

 

Correct me if I'm wrong, but the rear u joint has to be removed while the driveshaft is still on the car, right?

 

Viewed the CSM procedure?

 

No sir, but I will

 

Both the front and rear universal joints are pressed into the driveshaft and stay with the shaft. Two of the four needle bearing caps on the rear joint are held in place by the pinion yoke, straps and bolts. These two caps love to succumb to gravity and fall off during driveshaft removal launching at least one needle roller into the epicenter of nowhere. Rotate the driveshaft so that the two caps held by the straps are horizontal, carefully remove the driveshaft without dropping or having the caps come off the joint. Tape the caps in place until reinstallation.

 

Jeff - Thank you for jumping in. "Epicenter of nowhere" I love it!!!

Dave - Just (another) reminder, before removing any h/w, create/mark a horizontal line on the driveshaft through the U-Joint so you have the original (correct) orientation of both the propeller shaft & the U-Joint for reassembly.

 

Back to my regularly scheduled weed whacking entertainment(?).

 

So once the straps are removed and the caps, the driveshaft can come out, correct? And is there a way to check the u joints once the driveshaft is removed?

 

If you want to check the u-joints, do that prior to removing the shaft. That way it is held in place and you can check for slop in the joints by grabbing the shaft and trying to rotate it back and forth, or move it up and down. The joints should be tight with no lateral movement.

edit: I forgot to mention the classic check for sloppy u-joints is listening for a "clunk" sound when shifting from Park to Reverse.

 

So the mark would be in line with the axle tubes, correct?

 

You "might" look at it that way. Imagine a line directly in the middle of the driveshaft all the way from the front of the driveshaft to the end of the drive shaft (pinion shaft) right onto the differential. You don't need a line that long, create a line on the parts you're removing as I have previously suggested - this/these lines can be used as a point of reference during reassembly. I guess I'll note as a precautionary statement (remember I haven't changed U-Joints on a '72 CS) this next. When you install new U-Joints ensure you install each one so the grease nipple (Zerk fitting) is in the/an accessible position. I don't know if OEM came w/ grease Zerks or whether you're buying U-Joints w/ grease Zerks (recommended) - just keep it in mind. Creating the line from drive shaft through the pinion shaft and (importantly) direct onto the pinion shaft nut then onto the differential will pay off when it comes to putting the nut back on (good reference for tightening that nut).

 

Here Dave - I couldn't have said it any better myself. Note the part about returning drive shaft to its original position/location. You got this Skippy.

 

Count the number of turns it takes to remove the pinion nut so it can be reinstalled to the same depth.

 

A couple stolen Internet images solely to demonstrate the marks (for alignment purposes).

 

That is good advice, as well. I scribe (mark/create) a line but about same idea. Hell, do both!

 

Dave - It really doesn't matter what orientation you create/scribe/mark a line - bottom, middle or whatever - you just want the line(s) in the same plane/orientation.

 

Dave - I'll toss this up as a bone. John has a 5 part series on Universal Joints. I'm only providing you with this video since it demonstrates alignment, blah, blah, blah. When I have the chance I like to post his videos because John is EXCELLENT.

 

Note that this works for removing / replacing the driveshaft, but when the u-joint is replaced you need the scribe mark to go onto the shaft as well so the yoke is put back in the correct orientation.

 

It was ONLY & SINGULARLY a visual aid. There was absolutely NO ATTEMPT on my part to provide step-by-step instructions complete w/ visual aids. I stated nowhere to create the mark(s) EXACTLY as indicated on either image. Geeze Louise.

 

Lighten up Francis.

 

OK

 

So I took it in to the shop today and got the pinion seal replaced. Drove from there to the grocery store and then back home. Checked it when I got home and there were 3 drops of fluid on the bottom of the center housing. I wiped it off and took it for a spin around the block then checked it when I got home...good and dry. Maybe it was just residual fluid from leak?🤔