12 Bolts

[Droff]

I've posted more than a couple times on changing out my 2 series carrier to a 3 series, still looking into things but would like some inputs (again) on a couple scenarios.

Both are 12 bolts.

 

1. 12 bolt posi with 3.08 gears, out of a '68 Chevelle SS. No info on condition other than operational, owner had a plan to use in his truck, but the carrier wouldn't fit.  $800.

The 'not fitting' part sounds odd, I would think he would have verified before purchasing (for $1200) - from a friend.

 

2. 12 bolt non-posi with 3.08 gears, out of a Cutlass, year not specified but it will fit my '71. No info on condition other than operational. $350.

The seller has worked with diffs for many years.....sounds like he knows his rear ends...... (that was intended).

 

Information provided is from the seller, nothing verified yet.

 

So, with these two options, which would you pick, given this information?

[Leghome]

With the Cutlass rear end you could always make it a posi-traction unit before installation if you wanted too.

[Sam (Bones)]

a 3.08 is not a common gear for a Chevrolet, these 12 bolts could be BOP axles, which are different from a Chevrolet 12 bolt

[Droff]

I don't have numbers from either rear end, but it looks like a '68 could have come with 3.08s and posi, unless I'm looking at the chart wrong....

http://www.chevellestuff.net/1968/rear_axle.htm

 

I haven't done a check on the Cutlass, but I would imagine it would be a BOP.
What are the relevant differences I'd need to know? The seller mentioned something about either the pinion or the ring being different somehow, can't recall at the moment.

[Leghome]

My 72 has a BOP 10 bolt rear end. It is a 8.2 instead of the 8.5. I do not know the difference between them. When I bought the car 5 years ago I got all of the paperwork with the car for all of the parts the previous owner had put in the car. He ordered a 8.5 Richmond posi unit and had to send it back and get the 8.2 posi unit.

[Droff]

Found some info here, this is a very good info site although a bit light on MC info..

http://chevytalk.org/fusionbb/showtopic.php?tid/201627/

 

Then also found this on carrier info..

"Chevrolet generally used three different types of differentials for the 12-bolt: the Two Series carrier, the Three Series carrier, and the Four Series carrier. The “Two Series” has little use in a hi-po application and should be avoided if at all possible. The Three Series carrier accepted ring and pinions that ranged from 3.08:1 to 3.73:1, while the Four Series carrier accepted ring and pinions ranging from 3.90:1 to 6.14:1. While there are a number of subtle variations between the three types of carriers, a major difference is the thickness of the gear flange. Two Series carriers are the thinnest, while Three Series flanges are thinner than Four Series flanges. Because of the size of the flange, the carriers cannot be randomly used with ring and pinion sets from the trio of “families” (unless, of course, special gears with custom ring gear mounting surfaces are used. These special gears are readily available from Richmond Gear). Additionally, the Two Series carriers do not have any webs on the top of the carrier. Three and Four Series carriers do have webs."

[Jared Richey]

Just don't get stuck buying a bop 12, it's not a genuine Chevrolet 12 bolt. All the stuff is different and it's not a true 12 bolt, I believe the inside gear is smaller than a Chevrolet, the outside cover gives it away it looks like a 10 bolt cover... some people have been ripped off buying these things a Chevrolet rear ends. Now the 68 and 69 at least the Vista Cruiser came with Chevrolet 12 bolts but I do not know if the regular Cutlass car came with them or not. My 68 Vista has a Chevrolet 12 bolt.

[Droff]

That Cutlass 12 bolt I was referring too is a BOP, he pretty much told me that and the cover is a smooth cover. The $800 dollar 12 bolt is a GM, cover gives it away.

I've decided to change out the carrier on the 12 bolt I have and go that route. Dollar wise it's not much of a difference as buying one already set up.

Thanks.