I had the usual left side differential cover leak. I was just about to reinstall the cover and was cleaning up the mating faces when I reached into the case to clean out any dirt that might have fallen in and found a loose washer. I've gone through the Service Manual, and it looks like it's a side gear washer. I have a number of questions:
1. Is it a side gear washer? Dimensions: 1 3/4" diameter, 17/64 thick (it looked like it was just a hair more than 1/4), 7/16 hole, 1/32 step is machined into the outer and inner corners, and there's an S stamped on one face. It had a some build-up of gunk, except for six equally spaced radial marks on both sides that were polished clean. There's nothing I can see in the bottom of the case that could wear off the gunk in that kind of pattern, so I assume it wasn't left there by mistake during manufacture.
2. What do the side gears do? The manual isn't really clear, nor is there a useful diagram. The "Description and Operation" section says the pinion gear rotates the ring gear(s), but doesn't mention the side gears.
3. I can't remove the differential myself, so fixing this will require moving the car. Obviously it got to my garage under it's own power. After installing the side cover and drive shaft, can I safely drive it to a repair shop, or should I have it flat-bedded there?
4. Does something have to break for this washer to come off? Am I looking at a major repair? If so, I'm inclined to have a new differential installed rather than hope that I can get a mechanic who can fix it properly. Plus, if my leak is from a porous casting rather than from the O-ring, maybe a new diff will prevent the leak from recurring. Advice?
5. I've had two problems that might suggest when the washer fell off. First, this might be related to a previous thread where I asked for suggestions about remedies for my Traction Control cutting in too early. Here's that thread: Traction control engages too early out of corners
Is it possible that this washer could have come off at least 1500 miles ago and caused the problem with Traction Control intervening excessively on corner exits?
6. One of the suggestions in that thread was to do some burnouts and see if the limited slip was working to keep both wheels spinning. I did that, and the results were uncertain. I did about 8 burnouts on various surfaces ranging from slippery pavement to gravel. Every time both wheels spun, based on feel and the appearance of the tracks, but twice one side spun a fair bit more than the other. About half-way through the series, while I was backing up to look at the track, I heard a mechanical rattling that sounded like it came from the rear end. I stopped, then moved back and forth a number of times and couldn't reproduce it. I wasn't sure what I had heard, and I was focused evaluating the limited slip, so I carried on with the burnouts. Could that have been the sound of the washer coming off?
7. The two times that one side spun a lot more than the other, I chose spots for the burnouts where there was a difference in available traction between the wheels. Is it normal for one wheel to spin a lot more than the other when one wheel is on clean pavement and the other is on sand-covered pavement? Or does it point to a problem with the limited slip? (If the limited slip is defective and that isn't related to the loose side gear washer, then that would be another reason to get a new differential.)
The side gears are what make the differential a differential. They "orbit" the left and right primary gears (27 & 30 on the drawing). The ring gear drives the "differential case assembly" and the side gears inside that assembly are anchored to the case, and their teeth are what drive the left/right output shaft gears. Without the side gears, the axle doesn't turn.
There's no way I can imagine that you could lose one of the side-gear washers from inside the differential case assembly (#16 on the drawing) and still have a functional, non-grenaded rear end. They simply can't "fall off". And looking at the assembly drawing, there is very little chance that the washer was "left off" during assembly at GM. The differential case assembly is assembled outside of the external case (labeled #7 - Carrier), and then inserted. If they'd left a washer off, it'd still be in the parts bin. And while the drawing doesn't actually show how the side-gears install inside the case assembly, I further bet those washers are critical in preloading the side gears against the driven gears. If GM had left one out of the differential, the differential would have long since failed.
No..., I would guess that the part you're looking at is #38 on the drawing, labeled "Shim". That's consistent with the letter "S" stamped on the part, and also is the only component I see that is likely to come off the output shaft as you remove the left side cover. The "stack" of parts left-side are, output shaft seal, differential carrier left-side cover... these first two parts are "external components", then inside the cover you have... cover/shaft bearing, shim, output shaft bearing race, output shaft bearing, differential case assembly (with the shaft extending out from the differential case assembly).
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While you were posting, I was talking to a mechanic friend, and I now have a much better picture of how a differential works. What you've written makes perfect sense to me too, now. You and he (and me too, not that my opinion counts for much) agree that there's no way the washer could be from a side gear.
I think the hole in the washer is too small for it to be the shim you describe. If I understand your suggestion correctly, the output shaft of the diff would have to fit through it, and that's not possible.
My mechanic friend asked if it was magnetic, and that's the answer. It's a magnet! He says most differentials have one somewhere, and mine must have come loose or was never fastened down properly. From the regular pattern of goop and clean metal I imagined it must have been doing some job somewhere until recently, as I couldn't see how that pattern - exactly the same on both sides - could arise while it was rattling around in the bottom of the case. But I guess fluid flows can do strange things. I suppose the fact that there were no metal shavings stuck to it is a good sign that the differential gears are in good shape - the only good thing about this episode.
I'm still open to ideas (especially about whether my burnout test results mean my limited slip is wearing out), but I think the immediate problem is solved. I have to figure out where the magnet belongs - I don't think the manual mentions it so suggestions are welcome - and put everything back together to test it out.
The magnet is pictured, it's #39 on the component locator drawing for the differential carrier/case. Doesn't say anything about where it goes, it's possible they just throw it in loose.
Hmm, I guess you have a different year - my Service Manual is for 2001. None of my numbers match yours. My side gear washer is #22, not 16, the shim you mentioned is 31, not 38, and the magnet is not shown - my numbers end at 33.
It's a bit disappointing that no one who's done this job bothered to explain the function of this washer. You really can't miss it once you get the side cover off. A few years ago a dozen guys would have been tripping over each other to get in the first answer. Sadly, with all the posts from vendors, the other board doesn't have any more useful posts than this one.
The magnetic "washer" goes into a "holder" in the bottom of the differential case. IIRC, it just slides into the holder and is not fastened there in any way.
You might be able to get it back into its slot with the side cover off. I've got a bunch of spare differential parts out in the barn and tomorrow I'll have a look-see and get back to you. HTH
Jimbo
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The magnetic "washer" goes into a "holder" in the bottom of the differential case. IIRC, it just slides into the holder and is not fastened there in any way.
You might be able to get it back into its slot with the side cover off. I've got a bunch of spare differential parts out in the barn and tomorrow I'll have a look-see and get back to you. HTH
Jimbo
Thanks, Jim, but once I realized it was a magnet instead of a washer it became obvious where it belongs. Just looking at the diff housing it looks like there's nothing to hold it in place, but there's a little tab on the side cover that keeps it from coming free. My problem was that I swept it right out of the diff onto my chest while lying under the car and wiping up the oil in the bottom of the case. It didn't occur to me to consider that it belonged in there since it came out so easily and had no visible function.
The car's all back together. I'm hoping the new O-ring and the sealant recommended by the TSB will solve the leak problem, and the issue with the limited slip will go away for at least a while with new synthetic fluid and friction modifier.
You said the magnet had some buildup of gunk when it came out. That's accumulated metal from the diff gears. If you left the magnet out when you reassembled the diff, you're going to want to increase your fluid flush interval to compensate.
I installed a magnetic drain plug the last time I changed the fluid in my rear diff. Probably serves the same purpose as the stock magnet your talking about....
LR, the only thing I'd be concerned about is that the drain hole for the Diff is pretty high up on the case. You fill the Diff until the oil is at the level of the hole, so if you ignore splashing and thermal expansion of the fluid, you could sort of say that the drain plug is "dry". You really want the magnet at the lowest point so it's bathed in fluid, and so that when the car is stopped any metal in the fluid will precipitate out to that lowest point to be captured by the magnet.
RS, Im not sure Im following you. There is two plugs on the rear diff. One to fill and one to drain. The magnetic plug I installed is for the drain and threads in at the bottom of the rear diff (if I remember correctly, its right next to the center of the rear subframe crossmember).
How/why would the drain plug be at a high point in the rear diff if you were using it to effectively drain the rear diff fluid?? And is it really usually dry??
Ahhh. Well. I'm something of a space cadet of late. There's another plug at the bottom of the Diff? Makes sense, though I don't remember one, I'll defer to your direct experience. RocketSled = Dufus.
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