Marks on differential case

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  #1  
Old 04-07-17, 02:02 PM
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Marks on differential case

Replace diff fluid in 1999 F150 recently. Have never really played with a differential so not sure what "normal" looks like. Didn't find any chipped teeth or anything I would consider irregular. The gear teeth all looked like uniform wear.

The only thing that caught my eye were these grinding marks on the differential case that surrounds the planetary gears. You can see about 9 of them in this picture.

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It looks like they are all uniform distance apart. Do they grind the cases in order to have balance? Since the case spins when driving, I'm not sure where inside the differential the marks could have come from. The only thing being the pinion shaft gear. But that would mean the case was held steady at regular intervals for these makes to have been made. Which seems unlikely.

Just curious?

Edit: Could somebody rotate the picture 90 degrees clockwise so no one gets dizzy.
 

Last edited by PJmax; 04-08-17 at 11:14 AM. Reason: rotate pix
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  #2  
Old 04-07-17, 02:29 PM
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Those marks look about where the pinion gear comes through case. Spacing looks about the same. Is there any slop in pinion shaft where it comes into case? Don't remember ever seeing that before.
 
  #3  
Old 04-07-17, 02:39 PM
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There was no play in pinion gear. And pinion gear looked unmarked/unscratched. I just can't see these marks being made at random (which would occur if it happened inside the case during normal operations). They are too uniform (especially since the diff case spins/floats/moves when in use. Almost like a grinder had been taken to it to remove excess material. Case cover had what looked like original black RTV on it.
 
  #4  
Old 04-09-17, 05:58 PM
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It looks like it would have been made by pinion teeth at some time. Are you the first into the case or is a few off second owners? The pinion would be forced away from the planetary case, but if the side bearing on either side of the ring gear or a pinion bearing had gone out the pinion could have done that. For what you have now I would check those bearings/ for play.

The planetary case should be on a solid lateral line.
 
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Old 04-09-17, 08:42 PM
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Second owner, but it appeared to have never been opened. But not positive. I used a small HF prybar to try and see if there was any deflection as I inspected it and everything was solid, no play. Diff hasn't given me any problems, just changed fluid as prev maintenance.

As I mentioned, I could see the pinion gear and it looked unmarked, so I would guess it's not the culprit. Also, the grinding marks are very regular. Like someone did it to remove specific material. That's why I asked the question about balancing the diff case.

Diff works fines, I was just curious. Cover is back on and all sealed for another bunch of miles.
 
  #6  
Old 04-10-17, 07:25 AM
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Yep, if it's working don't mess with it. Those marks fall perfectly between the ring gear teeth. The only thing in the differential with that alignment is the pinion.

Hard to say.
 
  #7  
Old 04-18-17, 06:45 PM
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I worked as a tech at Ford dealerships, for 30+ years.
I know, from experience, what the marks are.
At some point in time, Someone replaced the pinion seal.
& did not get the pinion NUT tightened. CORRECTLY.
& the pinion gear Did come in contact with the differential case.

It is difficult to get the nut RE tightened.
TOO tight, & it will cause excess preload on the pinion bearings.
TOO loose will cause this(extremely-TOO loose).
 
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