12 bolt 4 series carrier question

**SS69chevelle** · #1 11-18-2023, 08:04 PM

Hello all, Does anyone know specifically what to look for on the 4 series carrier to determine if it is a COPO carrier vs the standard one? The carrier has black marker writing that says "r/b Moroso" which I assume means rebuilt by Moroso. The gears are 17-10 and new, the clutches are new and the unit does not look like it was run after the suspected rebuild. The carrier is dated C 13 J (Mar 13th 1969). With the parts is a box of 12 bolt posi carrier gears that are 16-10 and identified as COPO gears, do not know if they came from this carrier or not. Any help would be appreciated to determine if the carrier is a COPO unit or not. Thanks Andy

Attached a few pics for reference.

**DAVE H** · #2 11-19-2023, 02:15 PM

Trying to find this thread..

**SS69chevelle** · #3 11-19-2023, 03:01 PM

thanks, i have seen it and several others. I was hoping someone had pics of the copo case differences since most threads dont have any pics. Based on what i have found I thought this might be the best place to locate some pics that might define the specific differences. take care, Andy

**Hotrodpaul** · #4 11-19-2023, 03:10 PM

With those heavy springs it looks to me like a Moroso Brute Strength posi unit, are there any part numbers stamped on the outside of the flange?

**SS69chevelle** · #5 11-19-2023, 06:56 PM

The heavy springs had me thinking it was a Moroso unit, I checked the gears and the clutches, it is 17-10 but the clutch count is 18 total the standard for the 4 series not like the brute strength unit which has 22 total. the only stamped numbers on the unit are the date C 13 J . There are COPO carrier gears 16-10 with the parts i got but i do not know if they would work in this unit or not since a COPO carrier is machined differently. I am trying to see if i can confirm if it is just a standard 4 series or a COPO one. I am beginning to think it is a standard unit rebuilt by moroso back in the day and never used. I was hoping someone here might be able to proide an example to compare to. thanks Andy

**bbjohnny** · #6 11-22-2023, 01:12 PM

You can try and install the COPO gears and see if they fit. If it is not a COPO carrier and you install the side gears, you can't get the spider gears in with the stock clutch count.

**Kurt S** · #7 11-26-2023, 04:09 AM

Some info: http://www.camaros.org/carriers.shtml

**lbnaz** · #8 11-28-2023, 02:29 PM

is there anyway to identify that a posi is copo other than take it apart and count the gears. Here are some photos of one I have in a rearend. Appears to be 8 teeth showing on the spider gear but its hard to tell. The window openings look like the previous post. What are your thoughts. Thanks, Larry

**John Brown** · #9 11-28-2023, 03:06 PM

A round hole in the stamped steel spring plates is another indicator.

**big gear head** · #10 11-28-2023, 05:15 PM

Most 4 series cases have the small square hole. I've seen a few with the larger oval hole. but not many. All Eaton gear sets have 10 teeth on the pinion gears. They are 18-10, 17-10 and 16-10. Standard units from Chevy are 18-10. Eaton made a heavy duty unit that was also sold by Moroso that had 17-10 gears and the COPO units had 16-10 gears. New Eaton units have 17-10 gears that are made from powdered metal.

Your preload plates look like they have oval holes in them, which would not be in a COPO unit.

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