# 8.2 or 8.5?



## 71Goatwannabe (Jan 17, 2020)

I have been trying to figure out what read end is in my 71 lemans. 8.2 or BOP 8.5. It is dated for 71 so I assume it is the original (could be wrong). I’ve read that the square ears on the bottom mean 8.5 and that if it is even with the cover it is 8.2. Mine looks like it is neither. It’s not full square but it isn’t flush with the cover. Without taking the cover off is there a way to find out?


----------



## BLK69JUDGE (Jun 10, 2010)

looks like an 8.2
what else besides pulling the cover ?
casting number 
axle tube stamp 
drive shaft length center to center on u joints
pinion nut size
axle bearings 
reinforcement webs on the housing change
all are things that come to mind that are different 8.2-8.5


----------



## 71Goatwannabe (Jan 17, 2020)

Thank you for that 69Judge. That’s what I wanted to know. I was hoping it was an 8.5 lol. I plan on pushing a little bit of power and didn’t want to break the bank trying to find a 12 bolt.


----------



## Mine'sa66 (Oct 30, 2019)

71Goatwannabe said:


> Thank you for that 69Judge. That’s what I wanted to know. I was hoping it was an 8.5 lol. I plan on pushing a little bit of power and didn’t want to break the bank trying to find a 12 bolt.


Get the 12 bolt...you'll always be happy with it  What are you looking to spend?


----------



## LATECH (Jul 18, 2018)

For sure an 8.2

Get a yukon dura grip posi and toss it in. Plenty strong enough for a street build.


----------



## LATECH (Jul 18, 2018)

History and Identification of Chevy 10 and 12 Bolt Chevy Differentials


Chevy 10- and 12-bolt axle assemblies have been standard equipment on GM passenger cars, muscle cars, and trucks for decades. The rugged, reliable, and efficient Chevy 12-bolt has established itself as the preeminent rear differential for GM muscle cars since its debut in 1965. However, the...




www.chevydiy.com


----------



## 71Goatwannabe (Jan 17, 2020)

I’m leaning toward a 12 bolt or at least an 8.5 as from what I’ve read the 8.2 only is good till about 400 horse. Is that true? And I’m not really looking to spend all that much at least right now since the engine build has been a very expensive adventure. Also the 8.2 I believe has a 2.93 gear in it so my question is do Chevy 8.2 gears work in this? And I know the posi is BOP specific. Which bop posi are more expensive anyways. I might go see if I can convince my neighbor to sell one of his Chevelle 12 bolts that he won’t use.


----------



## PontiacJim (Dec 29, 2012)

71Goatwannabe said:


> I’m leaning toward a 12 bolt or at least an 8.5 as from what I’ve read the 8.2 only is good till about 400 horse. Is that true? And I’m not really looking to spend all that much at least right now since the engine build has been a very expensive adventure. Also the 8.2 I believe has a 2.93 gear in it so my question is do Chevy 8.2 gears work in this? And I know the posi is BOP specific. Which bop posi are more expensive anyways. I might go see if I can convince my neighbor to sell one of his Chevelle 12 bolts that he won’t use.


First, no, the Chevy 10-bolts are different. The Pontiac 8.2 can handle some power, it's when you start using posi and wide sticky tires with bigger HP and dump clutches, do roll-backs at around 40 MPH and drop it into Drive, figure-8's in parking lots, or add 400HP nitrous and 8-71 superchargers.

A 10-bolt will hold up better behind an automatic as the torque converter acts as a cushion. Slam-bang manual transmissions are harder on it overall.

They can take abuse, but have limits. With the right combo, you can explode a 12-bolt or 9". Also remember these parts are old and very worn. You can purchase items to improve durability over stock, but that doesn't mean you want to beat it like a red-headed step child, although I have in the past without failures.

The 8.5 is indeed stronger, but again, that is probably with a good rebuild. The 12-bolt and 8.5 are on par for strength according to my drag racing buddies who use the 8.5". Easier to find and cheaper, but my buddy has a BB Nova with leaf springs which makes them much easier to find. Coil spring applications are limited seeing they are only used a couple years for the A-body, like 1971 & 1972. A 12-bolt was used more years in Chevy, but they have C-clips and can/do break under severe usage and then you lose an axle and can tear up a quarter panel, or worse.

There is no inexpensive route. If you want to save money, use what you have. If you want more performance, then you will have to spend money to upgrade the gears, center section, bearings, possibly axles if you want stronger ones, and then labor if you cannot do this yourself. The other option is to try and find a complete rear end with what you are needing. 12-bolt's do not go cheap and can be hard to find. Then you are still taking a chance on it's condition.

I went with an aftermarket 9" as they have been around since 1957 and still going strong under race cars, muscle cars, hot rods, etc.. You can get them set-up to bolt into an A-body with the needed coil spring/shock mounts. I suspect the driveshaft may need adjusting in length, but not sure as I have not hooked mine up. Factory rear sway bars won't fit as they have a different center housing. Not an inexpensive set-up, but it is essentially bullet proof and mine is said to easily handle 600HP in the way I had it assembled. You can buy them complete or pick your parts as I did and then had it put together.

Same goes for the 12-bolt. You can buy aftermarket and have a new unit ready to go.

Once you start building up an engine past factory HP/TQ numbers, you usually have to upgrade transmissions, rear-ends, frames, suspensions, and braking.


----------



## 71Goatwannabe (Jan 17, 2020)

By 72 did they all have 8.5s? Couldn’t make a deal for a twelve bolt with the neighbor but I know a guy that has hundreds of 60s-70s pontiacs that he parts out with most of them mostly complete. And he has multiple 72 lemans sports would they have a 8.5?


----------

