# Hmmm... Inaccurate Differential Gear Notes From Auburn



## armyadarkness (Dec 7, 2020)

Anyone ever see this disclaimer on the Rons Machining Service? I can't imagine "drilling out" a ring gear. For some reason, Auburn doesn't even list a GTO or BOP application on their site... At least, not that I found. I've never heard of drilling out a ring gear, and even if the ring has 7/16 bolts, the carrier is 3/8, so unless there is a shrinking bit, something's not right.


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## 67ventwindow (Mar 3, 2020)

If you do a search on all HP differentials you will see they have three on the Auburn Gear site. Their configurator tool is not the best. They are listed as Chevy/GM on the model info, but they clearly say BOP. Maybe someone could help the with thier web site.


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## armyadarkness (Dec 7, 2020)

67ventwindow said:


> If you do a search on all HP differentials you will see they have three on the Auburn Gear site. Their configurator tool is not the best. They are listed as Chevy/GM on the model info, but they clearly say BOP. Maybe someone could help the with thier web site.


Thanks. Have you researched them? EVeryone seems to prefer Eaton over Auburn, but Auburn owners seem to love them, and they're oem equipment in several vehicles as well.


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## Old Man Taylor (May 9, 2011)

I have an Eaton/Moroso in mine, but it's a 12 bolt Chevelle rear.


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## armyadarkness (Dec 7, 2020)

Old Man Taylor said:


> I have an Eaton/Moroso in mine, but it's a 12 bolt Chevelle rear.


I have always heard Eaton, Richmond, and Auburn to be reputable... When I did my Jeep, I used Yukon 5.56's... I later heard that they were Chinese gears, but they installed fine and they spun 35"s with no issue.

So I ordered Auburn for the GTO, and then I saw such vast differences of opinion. I guess I'll see!


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> Anyone ever see this disclaimer on the Rons Machining Service? I can't imagine "drilling out" a ring gear. For some reason, Auburn doesn't even list a GTO or BOP application on their site... At least, not that I found. I've never heard of drilling out a ring gear, and even if the ring has 7/16 bolts, the carrier is 3/8, so unless there is a shrinking bit, something's not right.
> View attachment 139085



If I am not mistaken, the larger ring bolts are for the 8.5" (about 1971 and up) later rear ends, not the 8.2". I am not an expert on auto rear ends, just the rear ends on women. 

Just make sure you have the correct unit and do a trial measurement of what you have versus what you are installing. It certainly states 8.2", but in today's world, that can mean nothing.


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## 67lemans (Oct 30, 2009)

I recently replaced a 3.23 open with an Auburn 3.23 posi. (67 lemans). It was the only posi I found that was listed as fitting and it did. I have driven it and it is quiet and spins both tires as it should. For no more than I am going to put it through it should work just fine. I seem to recall there was two levels, base and then an heavy duty. Mine is the base, I think the difference was the spring load.


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## armyadarkness (Dec 7, 2020)

67lemans said:


> I recently replaced a 3.23 open with an Auburn 3.23 posi. (67 lemans). It was the only posi I found that was listed as fitting and it did. I have driven it and it is quiet and spins both tires as it should. For no more than I am going to put it through it should work just fine. I seem to recall there was two levels, base and then an heavy duty. Mine is the base, I think the difference was the spring load.


Good to hear. As another has mentioned, the Auburn site and search feature, stink. Bad.


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## 67lemans (Oct 30, 2009)

I got it at jegs. I spoke to a technician who was very knowledgeable. He knew the difference between the chevy and BOP 8.2 and got me the correct shims as well.


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## armyadarkness (Dec 7, 2020)

Auburn is in! I shouldve read the instructions better, because the tell you not to use synthetic, which I always do and did. However, the shim pack that came with the diff was a specialty item... BUT it had no instructions, so I didn't do that right either. Since I had to drain the diff and refill it, I got to take another crack at the shims, and now they're much better.

Full throttle below 20 MPH will kickdown (if the stars are aligned) and roast both tires. 

My initial review of the Auburn is very POSI!


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## 67Mac (Jun 16, 2021)

Replacing open 2.56 with a 2.93 and the Auburn grip n loc. My mechanic has the original out and is concerned the Auburn won't fit. Any help is much appreciated. The Auburn carrier is slightly taller. Apologies for jumping on this thread.


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## armyadarkness (Dec 7, 2020)

67Mac said:


> Replacing open 2.56 with a 2.93 and the Auburn grip n loc. My mechanic has the original out and is concerned the Auburn won't fit. Any help is much appreciated. The Auburn carrier is slightly taller. Apologies for jumping on this thread.


First off, nice use of the search function! So much great info here already.. so many miss it.

The obvious... If your old diff is already out, then it's easy enough to try the Auburn, without bearings, to see if it fits between the carrier bearing bosses. If not, then...

It appears that Auburn sent the right diff, assuming that what's in the box is actually what the box is labeled as.
If so, then are you sure that your rear hasn't been swapped out?
If it has not, then are you sure that your gears werent already changed?


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## armyadarkness (Dec 7, 2020)

BTW, I love my Auburn!


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## 67Mac (Jun 16, 2021)

Thanks for the quick reply! My mechanic has it up on the hoist and the meter is running. The Auburn unit fits without the bearings pressed on. Auburn engineering gave us a dimension to check and it was correct. I am about 99.9% sure the differential is untouched. I got the car in 1985 and it was bone stock except for craiger mags. Again I appreciate your help.


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## armyadarkness (Dec 7, 2020)

Maybe Im missing something, but if it fits without the bearings than it should fit with them. There are usually two large shims in there with the OEM carrier, so he'll just be leaving those out. Kudos for being able to you for being able to drive with 293's!


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## 67Mac (Jun 16, 2021)

I agree, I think it should work. Glad you like the 2.93s, I want to able to drive it some distance. My first choice was 3.08 but I couldn't find any. Thanks again and enjoy your day. 👍


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