1. 73Coupe

    73Coupe Senior Member

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    I recently acquired this 2.76 differential with the intention of swapping it out for the open unit in my NY. This weekend I built a holding jig and started to clean it up a little. I was hoping to just clean and paint, as it seems pretty solid and the backlash is tight. Also planning on replacing the pinion seal...

    Inspecting the ring gear a little closer, there are strange marks on the drive side of the teeth. The pinion doesn't appear to have them. I am wondering if this is "ok" or should I replace? I might be able to swap with the existing 2:76 set that's in the car now, if those are any better.

    Any gear experts on here that could interpret this?
    Besides the gears, bearings, case, how does one inspect the limited slip unit?

    IMG_6026.JPEG

    IMG_6029.JPG

    IMG_6035.JPEG

    IMG_6041.JPEG

    IMG_6038.JPEG
     
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  2. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    With that much pitting, you should probably replace the ring and pinion. What often happens is that a car quits running and somebody lets it sit. In time moisture collects on the top half of the ring gear where it is out of the oil and the gear starts to rust. Then, someone tows the car and the rust wears off but the pitting remains. This unit as is will not last long if installed and will probably continue to shed metal. It would be possible to transfer the ring and pinion from one case to another, the problem then becomes one of trying to duplicate the fit. The used unit has a wear pattern that is established, and when you move it a new location a new wear pattern will occur, this is not good for the longevity of the unit. Similar situation to putting the set of lifters from one used cam shaft to another. This unit looks to be a 489 case, so it should have clutch packs. You would want to replace those as part of any upgrade. The 489 clutch packs are still available thru Mopar, or Dr Diff will sell you the updated rebuild kit. Be sure to check all bearings carefully as they might well be pitted as well.

    Dave
     
    Last edited: Jun 24, 2019
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  3. 413

    413 Active Member

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    That is a cone sure grip. It doesn’t have any clutch packs.
     
  4. 73Coupe

    73Coupe Senior Member

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    Does anybody make a new set of 2:76 gears that y'all know of?
     
  5. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Looks like you (413) are correct, the 489 case appears to have used both styles. Cone type is not rebuildable other than to replace the unit. We always used clutch pack type sure grips as they were something of a pain to work on but at least they were repairable.

    Dave
     
  6. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    www.drivetrainshop.com

    Dave
     
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  7. 73Coupe

    73Coupe Senior Member

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    Dang, looks like 3.23 is as high as they go....

    Is there any way to test or inspect the cone type unit on the bench?
     
  8. jct

    jct Senior Member FCBO Gold Member

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  9. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    This may help.

    How To Recondition a Sure Grip Cone
     
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  10. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    My rear axle guy rebuilds them both.
     
  11. 73Coupe

    73Coupe Senior Member

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    Excellent, thank you. Very informative.

    I wonder how much they took off the ends of the cones? .010? .050? .100?
     
    Last edited: Jun 24, 2019
  12. gyknot

    gyknot New Member

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    I agree it probably sat for some time to develop the pits. I disagree though with saying it will not last long. I have run gear sets like this for thousands of miles with no issues whatsoever. That's not to say yours will last as long too, but unless you are putting major amounts of horsepower to them, in normal driving they will likely last a long time.
    Just my opinion. Keep in mind I am super cheap and had to learn to make do with whatever I had back in the day. Its a hard habit to break.
     
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  13. boltupal

    boltupal Active Member

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    Those gears are fine for street use.
     
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  14. 70bigblockdodge

    70bigblockdodge Old Man with a Hat FCBO Gold Member

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    2.76 is not hard to find, most want them gone for something like 3.55 or 3.91 (why?). I would look around you should be able to scrounge up better than that.
    They would probably be okay.
    I personally would just jam it in there and evaluate on the fly/drive. If it makes noise or does not make 2 black stripes on the road then decide what to do next.
     
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  15. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    I have a freshly rebuilt 3.55 S.G. in a 489 case for sale here.

    Mopar 8.75 3.55 S.G. 489

    I’ll also Have a couple of others that’ll be available soon, a freshly rebuilt 2.94 S.G. In 489 case and a 3.23 2 pin S.G. In a 742 case that seems to be in good bolt-in condition.
     
  16. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Given that you are going to spend about $700-$800 to rebuild this unit and replace the gears, Bigblockdodge and others have a point. Depending on how much you drive the car, you might not put enough miles on it for the pitted gears to matter for some time. This gear set is far from perfect, but if it lasts for several years with only occasional driving, you can always spend the money when it fails. I would not drive this gear set cross country, but if occasional pleasure driving is all you do, trying it out to check it will not cost you much other than the bother of having to pull it out again.

    Dave
     
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  17. 73Coupe

    73Coupe Senior Member

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    Given the fact that 2.76 gears are not available new (right?...I don't see any in the above linked suppliers websites) my options are very limited. It took several years just finding this unit as-is. And when you buy parts off the internet you're always taking a risk no matter what the seller says....even if they are being honest according to their knowledge and skills and think their stuff is good. I could search a few more years and find another 2.76 R&P and end up with the same sh*t.

    I recall being offered a differential a couple years ago in my search, and was sent photos of a unit poking through a pile of leaves outside. The seller said they were "good" and wanted $400. Even though he refused to define what "good" meant and couldn't back it up with any details of pics....I can only imagine what those gears looked like....:BangHead:

    Anyways, I think I'll just throw it in and see how it sounds/works. The car is no longer my daily but I use it for long trips. I'm sure it'll be fine....and I can monitor metal loss by listening for the backlash clunks if they develop.
     
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  18. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Another way to monitor metal would be to find a fill plug with a magnet on the base, we used these years ago on the race units.

    Dave
     
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  19. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    I waited to hear what everyone else had to say before I tossed in my 2 cents.

    I'd run it.

    The worst that will happen is it might be a little noisy, but you won't know until you run it.

    IF... IF it gets worse, it's just going to get noisy and "sloppy". The teeth aren't going to shear off and leave you stranded... and you are going to have plenty of warning before it gets really bad.
     
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  20. 68PK21 440.6bbl

    68PK21 440.6bbl Senior Member

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    I'll toss my 2¢ in, just by enlarging the pics in this post I can see a lot of crap in this unit, I'd suggest a complete disassembly, cleaning and inspection. The pitting on the gears is pretty deep too IMO. Long highway drives could be a problem with this unit, driving around town you could get away with it. best of luck.