[dataway]

I'm a bit confused about differentials (among other things in life)

So what are the options for a 68 GTO with an 8.2 differential?

What confuses me is that I know certain carrier assemblies will accept a certain range of ratios .. in my case 2.93, 3.23 etc. Parts for these original 8.2 carriers are getting very hard to find.

If I want to keep my original rear axle, but upgrade the differential to something with more options and better parts availability, what are my choices.

B-man has suggested an Eaton posi unit, which looks like a good choice to me ... but what exactly does this change mean? Would more common GM 8.2 parts work with it? Would I be stuck with proprietary parts specific to that particular brand/carrier?

Car is stock, no high HP, and has an auto trans.

I guess what confuses me most is when I see the various types mentioned, like 8.2, 8.25, 8.5 etc ... does this ALWAYS indicated a different differential CASE/AXLE? Are 10 bolt rears always 8.2, 12 bolt always 8.5? etc.

I'm not asking because I'm planning any impending change, it's more of an educational question.

Thanks.

[tempest1964]

Hopefully ol' pinion head will chime in. He seems to be pretty well versed on rear ends. I think I spelled his user-name wrong.

[Jay S]

Auburn makes a carrier yet for the 2.93 to 3.23 range 8.2 gears.

https://www.summitracing.com/parts/aub-546099#overview

3.36 and lower takes a different carrier, Eaton make those as well as some other companies. Quick performance offers a carrier, gears and bearing kit for $650, which is a pretty good value IMHO. It is a kit for the 3.36 and lower gear ratios, 3.36 is a few extra $$. No one offers gears for bop 8.2 for 2.93 to 3.23, OEM is the only option now.

https://www.quickperformance.com/GM-...e_p_23027.html

[64-3Deuces]

Originally Posted by dataway

...
I'm not asking because I'm planning any impending change, it's more of an educational question.

Thanks.

If you're looking for a general overview this Hemmings article may help:

https://www.hemmings.com/stories/art...p-rear-axles-2

[Shiny]

Originally Posted by Jay S

...No one offers gears for bop 8.2 for 2.93 to 3.23, OEM is the only option now....

Wow, this is surprising, given all the advice on the forum supporting 3.08 as a desirable ratio.

So used gear sets must be worth something. I tossed mine a few years ago...

Note to self: don't assume any Pontiac part is worthless.

[68 Firebird]

My car had 70,000 with original 3:08’s. But pinion bearing was noisy.
Installed new Auburn posi while reusing original gear set.
Set pinion bearing depth using same shims. Crush washer was a royal
PITA. Set backlash same as recorded before disassembly.
Pattern verified before and after. Rear is perfectly quiet.
Could not be happier. Also had new bearing out on axles shafts as well.
That was some 12 years ago!

Gerry.

[NeighborsComplaint]

Auburn, Eaton, Yukon are all reliable differentials for your application. Yukon is a reliable clutch-type similar to Eaton and sells for $400. You can get a complete kit with osi diff, bearings and ring and pinion or just posi diff and ring and pinion since you have the rest.

[Cammer-6]

just remember its a BOP 8.2 vs a Cheby 8.2

[Jay S]

12 bolts are 8.875” ring gear


10 bolts come in a couple different configurations and are all different.
8.5” 10 bolt, 8.5” ring gear, uses a pinion design from a 12 bolt

10 bolt chevy 8.2” ring gear, c clip axles
10 bolt 8.2”BOP, bolt in axles
then with in the BOP families, 8.2” Buick, 8.2” Olds, and 8.2” Pontiac all have some differences.

There is also the type O 12 bolt, used by Olds, smaller ring gear than a typical 12 bolt, they are there own design.


You can still buy parts for a 8.2 BOP to keep it running for a long time. On something stock there is no reason to change directions IMHO.

[Rar_421]

At one time Yukon offered a kit to use Chevy gears in the Pontiac 8.2 so you could get gears like 3.42/3.23 etc,not sure if it's still offered though
https://youtu.be/QvGsrxQNass?si=Rz41liMnQmVNhMN9

[Formulabruce]

my '68 GTO had a 3.08 open sitting behind a Very Very heavy Dearborn M-13 and a 400 2bbl... Factory!
There are some great aftermarket ( clone) 12 bolts and 9 inchers that fit these.

[dataway]

The main aspect I'm not understanding is ..

What is the "Break" that determines when a completely different CASE is used. For instance with an OEM 8.2 Pontiac diff CASE ... what carriers will physically bolt in with a gear set? Just 8.2 BOP and aftermarket products?

In other words something like "8.5" describes not only the carrier and ring gear size, but also a diff CASE unique to the 8.5 carrier size?

And do ... 8.2, 8.5 etc all have different diff CASES as opposed to just different carrier sizes in the same size diff CASE.

PS. OK, reading the Hemmings article is clearing things up.

[b-man]

Originally Posted by dataway

The main aspect I'm not understanding is ..

1) What is the "Break" that determines when a completely different CASE is used. For instance with an OEM 8.2 Pontiac diff CASE ... what carriers will physically bolt in with a gear set? Just 8.2 BOP and aftermarket products?

2) In other words something like "8.5" describes not only the carrier and ring gear size, but also a diff CASE unique to the 8.5 carrier size?

3) And do ... 8.2, 8.5 etc all have different diff CASES as opposed to just different carrier sizes in the same size diff CASE.

PS. OK, reading the Hemmings article is clearing things up.

1) Yes
2) Yes
3) Yes
In a nutshell every different ring gear size (8.2 & 8.5 10-bolt, 8.875 12-bolt, etc.) has its own case or housing to accommodate that particular size.

Different gear sets will only fit on certain carriers/differentials (open or posi).

For the BOP 8.2 10-bolt there’s one that fits 2.56 & 2.78, another that fits 2.93, 3.08 & 3.23 and finally another that fits 3.36 and higher numerical gears. The 8.5 coporate has one that fits 2.41 & 2.56 and another that fits 2.73 and higher gears.

[dataway]

OK, got it, thank you sir.

So there is no way anyone will ever put 8.5 parts in a 8.2 diff CASE ... but aftermarket 8.2 upgrades are available.

B-Man ... I blame you for sending me down this road ... I'm seeing bad pictures in my head of much more dramatic acceleration than my current open 2.93 As a kid I had a good friend with a 69 Lemans (350, 4brl ), mildly modified, with a 3.23 posi that would keep up with my stock GTO ... I never forgot that.

Still ... it will have to wait a couple of years.

['ol Pinion head]

Originally Posted by dataway

OK, got it, thank you sir.

So there is no way anyone will ever put 8.5 parts in a 8.2 diff CASE ... but aftermarket 8.2 upgrades are available....

No 8.5 parts will fit in a Pontiac 8.2 carrier. The carrier bearings for a 28 spline 8.5 carrier are the same, that's it. To get to all of the strength advantages of the tapered bearing axle 8.5 A-body rear, have to start with an 8.5 housing & the desired differential & axles.

As far as "UPGRADES" to any of the differnt styles of 8.2 GM rears, upgrade is a very slick term. For those that are determined have an original early 8.2 Pontiac or early Buick 8.2 10 bolt under their ride, the first thing I always check are the original axles & sealed axle bearings. Until that sealed axle bearing is pressed off, & the axle mating surface examined, no peace of mind.

[will slow gto]

Originally Posted by Shiny

Wow, this is surprising, given all the advice on the forum supporting 3.08 as a desirable ratio.

3.08 is also available in 12 bolt and 8.5 10 bolt so that might be why.

[b-man]

Well the 12-bolt had a 3.07 but close enough.

I loved the 2.56 gears I ran in my Tempest with a 068 cam 455/TH400, I was running a short 25.25” 235/45-17 tire so it’s pretty much equivalent to a 2.73 or 2.78 with a taller tire. Still ran in the high-13s at almost 102 mph crossing the line in 2nd gear, it could run 140 on the highway (one time )

I currently have a 8.2 with a 2.56 gear in my Le Mans with a 421/TH350 and a 26.7” tall 215/75-14, when it’s time to put a decent rear end in it I’m going with a 2.73 geared 8.5 with a factory posi. It’s an air-conditioned cruiser but it will still get out of its own way.

The 3.08 is a nice compromise between stoplight acceleration and highway comfort. I would say 3.23s are kind of in that category but leaning more towards stoplight fun.

We have a member here (taman) who was solidly in the 10s with a 600 hp street 455 running a TH350 and 3.08 gear and amazingly was pulling down 16 mpg on his drive to the track.

[geeteeohguy]

Originally Posted by dataway

OK, got it, thank you sir.

So there is no way anyone will ever put 8.5 parts in a 8.2 diff CASE ... but aftermarket 8.2 upgrades are available.

B-Man ... I blame you for sending me down this road ... I'm seeing bad pictures in my head of much more dramatic acceleration than my current open 2.93 As a kid I had a good friend with a 69 Lemans (350, 4brl ), mildly modified, with a 3.23 posi that would keep up with my stock GTO ... I never forgot that.

Still ... it will have to wait a couple of years.

That Lemans could keep up with your GTO....until about 100 mph. Back in the late '70's my 66 GTO with 3.55's really ran hard. My buddy had a '67 with a 2.93 and he was envious. Until we got on the highway. He walked away from me easily after 100 mph. And his car got better mileage and ran cooler, too. I swapped a 2.56 Safe-T-Track into my '67 GTO about 12 years ago and love the mpg and easy 80 mph cruise speed. On a recent 2700 mile trip to Colorado, I averaged 20.6 miles per gallon.....most of it at 80 mph.

[dataway]

OPH, new sealed bearings on the axles, they look great, like new. Don't imagine they ever got much abuse with the automatic and normal size tires.

geeteeohguy ... Yes you are absolutely correct ... but you know, school parking lot counted for a lot more than top speed With the 2.93 I'd get a solid 17-18 mpg back in the day. Not sure what the top speed was ... but I had the speedo needle wrapped around to the "B" in the parking brake light a few times

[1968GTO421]

Curiosity - What would be the engine torque/HP limits be for a 8.2 axle in a 1968 GTO with TH400 (stock convertor) and 428?
Asking for general street/highway use and maybe a test and tune at the local 1/8 mile.
Thanks.

(Apologies to Dataway, not trying to hi-jack, just thought it fir in with your inquiries.)