Best Street/Strip Differential Carrier for GM 8.5

Michael Bennett

Greasemonkey
Jun 7, 2018
110
28
Okay, so the 30 spline Auburn posi I scavenged out of a Caprice 8.5 is starting to give up the ghost. Starting to one wheel peel at the drag strip and sometimes on the street. I've got another Auburn in my pickup that I bought new and that one didn't last either so I'm looking at other options. Thinking the Detroit Truetrac is the way to go. Haven't really heard anything but good things about them. I'd consider an Eaton limited slip but can't find one in 30 spline and I don't want a Yukon or one of the other knock offs.

Let me know what your running and what has worked good for you.

Malibu.jpg
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
3,612
113
Upstate NY
Quick's sells a deal of a clutch style posi from Yukon. Buy a 30 spline unit and get the axles from them as well. We paid around $700-750 for Moser axles, Yukon posi, gears and bearing kit.

Those Auburn units are turds IMO.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,786
113
I don't know about the aftermarket Auburns, but I can tell you this, back in the day when you could order up a 4th gen Camaro SS from Chevy (converted by SLP Engineering), one of the "upgrades" was the Auburn posi carrier (all Z28 Camaros had posi anyway) and they turned out to be pure garbage. LOTS of problems with those rear ends. When I ordered my 2002 SS, I shied away from that "upgrade". Glad I did.

I will never buy an Auburn. With that said, I agree about the truetracs. Heard nothing but good things about those things. Pay once, cry once.

Truetrac and Lockers are the only Eaton rear diffs that are specifically built to withstand circle track and drag racing. The Truetrac is more versatile as it covers restoration and street/muscle too.

Eaton Differential Quick Reference.jpg


PDF file with the Eaton application guide.

 
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Michael Bennett

Greasemonkey
Thread starter
Jun 7, 2018
110
28
I don't know about the aftermarket Auburns, but I can tell you this, back in the day when you could order up a 4th gen Camaro SS from Chevy (converted by SLP Engineering), one of the "upgrades" was the Auburn posi carrier (all Z28 Camaros had posi anyway) and they turned out to be pure garbage. LOTS of problems with those rear ends. When I ordered my 2002 SS, I shied away from that "upgrade". Glad I did.

I will never buy an Auburn. With that said, I agree about the truetracs. Heard nothing but good things about those things. Pay once, cry once.

Truetrac and Lockers are the only Eaton rear diffs that are specifically built to withstand circle track and drag racing. The Truetrac is more versatile as it covers restoration and street/muscle too.

View attachment 174152

PDF file with the Eaton application guide.


At 21 years old, I ordered a Z28 SS in 96. Took 3 dealers before I found one that would even look into ordering one. The first two didn't believe me. I think the Zexel torsen was an extra $1000 so I skipped it figuring the 7 5/8" rear would blow before the posi. Sure enough it lasted for the 33k miles I owned the car. The rear end was howling when I traded it in after who knows how many drag strip passes and a 21 year old me bang shifting it as often as I could.

Anyway, yeah I just ordered the truetrac. Been thinking about trying it and they are on sale right now so it's a good time to buy.
 

paul.m

Master Mechanic
Oct 20, 2018
380
43
I can say from experience that the Detroit lockers are absolutely bullet proof ! the first one I had back in the 80,s were installed on a 79 jeep honcho 4WD with 17;40s on it . I did a many of clutch dump on that truck went from dirt to pavement more times than I can count ! never had a minutes trouble . That truck would smoke all 4 tires .One side note on the lockers they do make a slight clicking sound when turning slow in a parking lot . Or at least they use to.
 

melloelky

Comic Book Super Hero
Oct 22, 2017
3,279
113
mass
Quick's sells a deal of a clutch style posi from Yukon. Buy a 30 spline unit and get the axles from them as well. We paid around $700-750 for Moser axles, Yukon posi, gears and bearing kit.

Those Auburn units are turds IMO.
he's ^right,I had two that were bad out of the box,single track from the get go.returned both, they reported I did everything rite both times(the set up,limited slip additive etc)the last time I got a voicemail from Aaron in tech support laaate on a Friday slurring his speech🍻carrying on and on I'm "ultimately"having these unit failures because my car's very lightweight in the back...are you fu*king kidding me???
steer clear of the auburns.my buddy's got a truetrac in his fox body and it works well.
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
3,662
113
Western MN
I bought the $270 yukon from quick performance's ebay store (it is a Yukon but comes 'unbranded'. I blew it up with potential wheel hop and 3800rpm clutch dumps on drag radials at the track.

I bought a replacement truetrac from Quick. I called in and got a better deal than they had online.

1619614503367.png
 
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64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
3,612
113
Upstate NY
To be clear, an Auburn posi and an Eaton/Yukon clutch style posi are not the same. An Auburn is a non-serviceable unit. 'Auburn' is a brand of differential that is a clutched posi. But is not an 'Eaton style' clutch posi. An Eaton or Yukon clutch posi is serviceable with gears and clutches.

A Detroit Truetrac is a Torsen copy. Torsen was the company that developed a helical worm gear type for the OEM's. It is a type of posi that Eaton copied and renamed a Detroit Truetrac.

Unfortunately, GM never requested a Torsen for an 8.5/8.6 10 bolt diff.

Tearing apart a Torsen or Truetrac will identify why they are tougher and more expensive.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
5,786
113
Unfortunately, GM never requested a Torsen for an 8.5/8.6 10 bolt diff.
Why should they when you're pumping 200 or less whopping HP at the crank for most of the 1980s? It would be lucky to tighten up a balsa wood plane propeller. Would be nice though if they did drop the coin to put in an 8.5 torsen.
 
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