[GuyH]

Hi All, long time lurker here. I have a '67 Firebird 400 w/TH400. The diff needs a rebuild & I have some questions I'm hoping the community can help with. I use the car for back road and freeway cruising spring through fall seasons & have no intention of using it on the track or auto-crossing etc, just spirited fun driving. Have no plans or need to rebuild the engine at this stage, though for this car I wouldn't expect that any future engine refresh I'd have done would result in more that 425 or so hp.

The diff is an open 8.2 10 bolt BOP non C clip unit (original to the car) with a 3.08 ratio & is making noises I can't in good faith keep ignoring (I replaced the rear wheel bearings over the summer & was hoping that was the source of the noise, alas I was sadly mistaken ). I'd like to keep the 3.08 ratio.

1) Since I'm going there, should I install a posi unit? Appreciate this is totally subjective, but for those who have made the change does it make a big difference to the driving experience?

2) If yes to posi, I found an Auburn unit that will fit a 3.08 ring & pinion (p/n 546099) that seems decently priced. Is Auburn a good brand or should I consider others?

3) Should I replace the ring & pinion? No clue if the current pair are still good or not, I sense the noise is just bearing related, but is it good practice to replace as part of a rebuild?

4) If I do replace the ring/pinion, what's a good brand? Both Richmond Gear & Motive Gear make replacement 3.08 sets, is one preferable to the other or should I consider another brand? (eg Jegs sell a set in their own name for 10 buck less than the Motive Gear set they have listed)

5) Am I just overthinking this &, for the driving I do, should I get one of those no name rebuild kits that includes a posi unit & ring/pinion set off ebay?

Thanks in advance for your help guys, appreciate any comments, info, thoughts etc.

Guy

[steve25]

Yes, your over thinking it a bit.
If the rear is making noise all the time then there is a good chance that you will need to replace the gears also, so pull the cover now and take a good look.

I would go with the posi.

[Navy Horn 16]

Auburn is a good brand. It's been a few years since my buddy rebuilt his 8.2, but I remember that he had limited options then.

Yes, go with with the Posi. If you have to take it all out, put it back together with new/better parts.

[leeklm]

Keep in mind that 3.08 gears can be a little hard to find for the BOP rear...

Sent from my SM-G965U using Tapatalk

[Gary H]

Originally Posted by GuyH

Hi All, long time lurker here. I have a '67 Firebird 400 w/TH400. The diff needs a rebuild & I have some questions I'm hoping the community can help with. I use the car for back road and freeway cruising spring through fall seasons & have no intention of using it on the track or auto-crossing etc, just spirited fun driving. Have no plans or need to rebuild the engine at this stage, though for this car I wouldn't expect that any future engine refresh I'd have done would result in more that 425 or so hp.

The diff is an open 8.2 10 bolt BOP non C clip unit (original to the car) with a 3.08 ratio & is making noises I can't in good faith keep ignoring (I replaced the rear wheel bearings over the summer & was hoping that was the source of the noise, alas I was sadly mistaken ). I'd like to keep the 3.08 ratio.

1) Since I'm going there, should I install a posi unit? Appreciate this is totally subjective, but for those who have made the change does it make a big difference to the driving experience?

2) If yes to posi, I found an Auburn unit that will fit a 3.08 ring & pinion (p/n 546099) that seems decently priced. Is Auburn a good brand or should I consider others?

3) Should I replace the ring & pinion? No clue if the current pair are still good or not, I sense the noise is just bearing related, but is it good practice to replace as part of a rebuild?

4) If I do replace the ring/pinion, what's a good brand? Both Richmond Gear & Motive Gear make replacement 3.08 sets, is one preferable to the other or should I consider another brand? (eg Jegs sell a set in their own name for 10 buck less than the Motive Gear set they have listed)

5) Am I just overthinking this &, for the driving I do, should I get one of those no name rebuild kits that includes a posi unit & ring/pinion set off ebay?

Thanks in advance for your help guys, appreciate any comments, info, thoughts etc.

Guy

Better double check that you're looking at the right 3:08 ring and pinion for a BOP style 8.2" rear end. I don't think anyone makes anything numerically less than a 3:36 ratio for that style rear.

['ol Pinion head]

There are no aftermarket gear sets for the high ratio (2.56, 2.78) carrier, or the mid ratio (2.93, 3.08, 3.23) carrier. Nice used is all that is out there, have built with share of nice used 3.23's & sold numerous nice sets of 3.08 & 3.23 Pontiac 8.2 gearsets. There are no new cheap mid or high gear sets like for various other styles of 10 bolt differentials. For the Chevy 8.2 10 bolt, there are new 3.08 gear sets, though expensive. It can be adapted into a Pontiac 8.2 10 bolt.

Some bolt-in axle GM 10 bolt history that the new differential parts sellers should take to note of. Get a load of their parts applications, most other than Tom's Differential, have their heads up their @sses with their parts listings. The connotation "BOP" 10 bolt basically stemmed from the intro & sale of early Zoom ring gear spacers & gear sets... nothing more.

-EARLY Pontiac 8.2 10 bolt gear sets were used in '64-69 Pontiac 8.2 10 bolts. Also used in following '64-67 early BUICK 8.2 rears. Buick used their own cast 8.2 10 bolt housing, as well as machined axles from '64-67. These are known as the Early Buick 8.2 10 bolts. From over 35 years of original parts sourcing, all '64 442's, as well as '65 442's & lower horse '66 Olds 442's (& all 3 year F-85''s) were built with the weak Buick 8.2 10 bolt housing rears.

-Lower gear ratio factory posi ''65 & '66 Olds 442 Anti-Spin 8.2 rears used the same converging rib gray iron Pontiac 8.2 housing 10 bolts as were used in '66 GTO's & '66 Tempest/LeMans. This casting of center housing had more strength in the pinion nose area than previous 8.2's, but that's not saying a lot.

-During the '67 model year Oldsmobile introduced the Type "O" Olds 10 bolt rear. Olds needed what they perceived as a stronger rear than previous offerings & had managed to free up capacity at it their own axle plant. The Olds guys love to call the Type "O" a 12 bolt due to its smooth 12 bolt cover but this design is an 8.4" diameter 10 bolt ring gear rearend. Another serious "restoration" piece. The strongest built had 31 spline sealed bearing axles, but like other HD 10 bolts of the time, lacked the pinion support of the later 8.5 10 bolt rears.

-LATE BUICK 8.2 10 bolts was brought out for the '68 model. These are an oddball, LH carrier bearing same as a 12 bolt, pass side same as 60's 10 bolt. Designed for more torque capacity than previous Buick usage bolt-in axle 8.2 rears, but very hard to find some parts for. A few runs of new gearsets have been made. LATE BUICK 8.2's were not installed in Pontiacs or Olds products, just Buicks from '68-70.

-Pontiac in the late '69 model introduced the LATE PONTIAC 8.2 carrier & ring gear sets. 2.56's all the way to 4.33's. In '69 models, have personally only ran across the late gearsets originally installed in a few late '69 Firebird rears, not late '69 A-body rears or GP rears. That stated, a small amount of late '69 GP's & Pontiac A-body's have surfaced with late style PONTIAC 8.2 gear sets. Gotta check them before ordering new parts. All '70-72 Pontiac 8.2's were built with the late style Pontiac 8.2 ring & pinion. . Early Ring gear bolts were 3/8" rh thread with 11/16" headed bolts. LATE Pontiac 8.2 ring gear bolts are 7/16" LH thread with 3/4" headed bolts. This can make it "fun" if one is searching for a nice used original or NOS ring & pinion set to match up with a LATE Pontiac 8.2 10 bolt STT carrier.. One can however have an earlier carrier's ring gear flange bolt holes opened up 1/16". Can do the same on a new Eaton or Auburn carrier in order to mate with an original set of LATE Pontiac 8.2 gears.

Last, & this further addresses actual 8.2 10 bolt rear end strength/pinion support. Pontiac cast & machined their own nodular iron cast center housing to exclusivelyuse in their lower ratio Pontiac 8.2 Safe-T-Track rears beginning for the '67 models. Nodular iron Pontiac 8.2 center housings were assembled off this style of center housing for Pontiac's lower geared 8.2 STT rears. up through the '72 models. Pontiac engineers specified the nodular iron composition of the center housing in an effort to diminish pinion deflection under heavy torque loading of the ring & pinion in the center housing. The strongest HD 8.2 Safe-T-Track rears also received stronger hd forged axles. In an early Firebird, the 3.36 STT coded rear was as high a ratio (low numerically) as an early Firebird rear would come with the nodular iron center housing STT rear. Factory 3.55 & 3.90 posi coded early Bird applications were also built this way.

Would be remiss not to mention, one can spend a ton of $$$$ in aftermarket parts (posi carrier, new gearset, Moser axles, "performance" rear cover) and labor, building up a gray iron Pontiac 8.2 housing, & still not have as strong rearend as a factory Pontiac HD STT rear. Under a putt-a-round cruiser, even with a higher hp/torque engine build & 4 spd in front of it, a built up gray iron Pontiac 8.2 10 bolt may live for a long long time. A purpose built car/ set up to really hook up, even on repro polyglas G70-14's, eventually the shortcomings of the gray iron 8.2 will become evident. Its worse with small diameter low tooth count pinions, but i have encountered 3.23 gray iron 8.2 GTO rears that have scattered the ring & pinion under high torque loads. Need to wrap this up, tryed to hit the highlights.

[Rar_421]

Not sure if there still made,but Yukon had a kit to use Chevy gears in the Bop housing,I came across this while looking for 3.23's for my tempest
https://youtu.be/QvGsrxQNass

[68 Firebird]

I rebuilt my rear about ten years ago. like you she was a 3:08 open carrier.
Installed my factory gears(low mileage) with a new Auburn HP Posi and have no complaints.
Take your time and measure your backlash before disassembly and carefull when setting up
new carrier. I was able to setup mine in my garage with rear still in the car.

The only pain in the ass was setting crush sleeve on pinion!!!!!!!

Use additive that comes with posi and Dino gear lube and enjoy.
3:08 are a great cruise gear.
Gerry

[vertigto]

I went with the Auburn Pro series posi for 3.23s.

[rohrt]

I did it the hard way and swapped out the 8.2 with a nova 8.5 w/3:08s. Eaton posi.

[b-man]

Originally Posted by rohrt

I did it the hard way and swapped out the 8.2 with a nova 8.5 w/3:08s. Eaton posi.

Best way.

So much better parts availability and gear choices, plus the 8.5 is almost on par with a 12-bolt in strength.

[GuyH]

Thanks All, really appreciate your input here. It's given me some good food for thought on this.

'ol Pinion head - that information is fascinating, I love this sort of detail about our hobby. Thanks for taking the time.

Guy

[rohrt]

This really is some great info.

Originally Posted by 'ol Pinion head

There are no aftermarket gear sets for the high ratio (2.56, 2.78) carrier, or the mid ratio (2.93, 3.08, 3.23) carrier. Nice used is all that is out there, have built with share of nice used 3.23's & sold numerous nice sets of 3.08 & 3.23 Pontiac 8.2 gearsets. There are no new cheap mid or high gear sets like for various other styles of 10 bolt differentials. For the Chevy 8.2 10 bolt, there are new 3.08 gear sets, though expensive. It can be adapted into a Pontiac 8.2 10 bolt.

Some bolt-in axle GM 10 bolt history that the new differential parts sellers should take to note of. Get a load of their parts applications, most other than Tom's Differential, have their heads up their @sses with their parts listings. The connotation "BOP" 10 bolt basically stemmed from the intro & sale of early Zoom ring gear spacers & gear sets... nothing more.

-EARLY Pontiac 8.2 10 bolt gear sets were used in '64-69 Pontiac 8.2 10 bolts. Also used in following '64-67 early BUICK 8.2 rears. Buick used their own cast 8.2 10 bolt housing, as well as machined axles from '64-67. These are known as the Early Buick 8.2 10 bolts. From over 35 years of original parts sourcing, all '64 442's, as well as '65 442's & lower horse '66 Olds 442's (& all 3 year F-85''s) were built with the weak Buick 8.2 10 bolt housing rears.

-Lower gear ratio factory posi ''65 & '66 Olds 442 Anti-Spin 8.2 rears used the same converging rib gray iron Pontiac 8.2 housing 10 bolts as were used in '66 GTO's & '66 Tempest/LeMans. This casting of center housing had more strength in the pinion nose area than previous 8.2's, but that's not saying a lot.

-During the '67 model year Oldsmobile introduced the Type "O" Olds 10 bolt rear. Olds needed what they perceived as a stronger rear than previous offerings & had managed to free up capacity at it their own axle plant. The Olds guys love to call the Type "O" a 12 bolt due to its smooth 12 bolt cover but this design is an 8.4" diameter 10 bolt ring gear rearend. Another serious "restoration" piece. The strongest built had 31 spline sealed bearing axles, but like other HD 10 bolts of the time, lacked the pinion support of the later 8.5 10 bolt rears.

-LATE BUICK 8.2 10 bolts was brought out for the '68 model. These are an oddball, LH carrier bearing same as a 12 bolt, pass side same as 60's 10 bolt. Designed for more torque capacity than previous Buick usage bolt-in axle 8.2 rears, but very hard to find some parts for. A few runs of new gearsets have been made. LATE BUICK 8.2's were not installed in Pontiacs or Olds products, just Buicks from '68-70.

-Pontiac in the late '69 model introduced the LATE PONTIAC 8.2 carrier & ring gear sets. 2.56's all the way to 4.33's. In '69 models, have personally only ran across the late gearsets originally installed in a few late '69 Firebird rears, not late '69 A-body rears or GP rears. That stated, a small amount of late '69 GP's & Pontiac A-body's have surfaced with late style PONTIAC 8.2 gear sets. Gotta check them before ordering new parts. All '70-72 Pontiac 8.2's were built with the late style Pontiac 8.2 ring & pinion. . Early Ring gear bolts were 3/8" rh thread with 11/16" headed bolts. LATE Pontiac 8.2 ring gear bolts are 7/16" LH thread with 3/4" headed bolts. This can make it "fun" if one is searching for a nice used original or NOS ring & pinion set to match up with a LATE Pontiac 8.2 10 bolt STT carrier.. One can however have an earlier carrier's ring gear flange bolt holes opened up 1/16". Can do the same on a new Eaton or Auburn carrier in order to mate with an original set of LATE Pontiac 8.2 gears.

Last, & this further addresses actual 8.2 10 bolt rear end strength/pinion support. Pontiac cast & machined their own nodular iron cast center housing to exclusivelyuse in their lower ratio Pontiac 8.2 Safe-T-Track rears beginning for the '67 models. Nodular iron Pontiac 8.2 center housings were assembled off this style of center housing for Pontiac's lower geared 8.2 STT rears. up through the '72 models. Pontiac engineers specified the nodular iron composition of the center housing in an effort to diminish pinion deflection under heavy torque loading of the ring & pinion in the center housing. The strongest HD 8.2 Safe-T-Track rears also received stronger hd forged axles. In an early Firebird, the 3.36 STT coded rear was as high a ratio (low numerically) as an early Firebird rear would come with the nodular iron center housing STT rear. Factory 3.55 & 3.90 posi coded early Bird applications were also built this way.

Would be remiss not to mention, one can spend a ton of $$$$ in aftermarket parts (posi carrier, new gearset, Moser axles, "performance" rear cover) and labor, building up a gray iron Pontiac 8.2 housing, & still not have as strong rearend as a factory Pontiac HD STT rear. Under a putt-a-round cruiser, even with a higher hp/torque engine build & 4 spd in front of it, a built up gray iron Pontiac 8.2 10 bolt may live for a long long time. A purpose built car/ set up to really hook up, even on repro polyglas G70-14's, eventually the shortcomings of the gray iron 8.2 will become evident. Its worse with small diameter low tooth count pinions, but i have encountered 3.23 gray iron 8.2 GTO rears that have scattered the ring & pinion under high torque loads. Need to wrap this up, tryed to hit the highlights.

[Shiny]

Originally Posted by rohrt

This really is some great info.

Agree and truly grateful OPH is willing to share all this with the rest of us.

[carcrazy]

As noted, you can spend a ton of money on the 8.2 differential and still end up with a rear that is not all that strong. I've learned this the hard way and have never had any luck with them on any of my GTOs (even the auto cars). Unless originality is important there are better options out there.

[mchell]

Fwiw
Never had a problem with a 10 bolt (1971)until I moved to the low 12”s / high 11”s on sticky tires….. 3900+ weight class

IF you are not looking to push power past 400hp AND your always going to be on street tires, I wouldn’t worry about it. Had very good luck pushing the 10 bolt to its max using a aluminum housing cover with built in bearing preloads….. seemed to make it last waaaayyy longer than I expected given I was tearing it up at the track pretty much every weekend.

Of course those days are gone and the 10 bolt DID NOT like 1.5x 60’s at all….. so bye bye 10 bolt

Never did break an axle, but I did blow the ring and pinion up….

[rustedgoat]

You should list your location in you profile. You could also consider just picking up a cheap used 8.2 open rear locally. I know if it was an a-body those rears go for cheap. Then you can rebuilt yours as you want with no downtime.

[Goatracer1]

Be true to yourself. You said you don't need a high performance rear end. If you are not racing the car there is NO way in the world you need a posi unit. If you do spirited driving on winding roads you are better off without a limited slip diff. OR do you just want to tell people "I have a posi unit"? Also check your ring and pinion and if there is nothing wrong reuse them. Used ones are likely to be no better than yours. Why buy new if you don't really need them. Again be honest to yourself about what you really want/need.

[Schurkey]

Thanks, Ol' Pinion Head.

Your post has been saved to a text document for later study.

Appreciated.

[GuyH]

Thanks again Guys for your input. this is good stuff.

Goatracer1 -
Yes I am starting to lean this way, given the lack of aftermarket stuff for a 3.08 ratio & the driving I usually do, I was genuinely interested if the posi would add much in the way of a performance upgrade (heh, certainly not for bragging rights, pretty sure anyone I know couldn't care less . ).

Cheers Guy