I just scored an 86 SS Monte Carlo posi Auburn Posi carrier with 3.73 gears for $90 at a dirt track swap meet this past weekend.
The guy said the carrier was out of his SS Monte that he traded in with 100K on the gears. The unit is sweet condition. But the unit was marked as seen below. I was wondering if the 10 bolt and 9 bolt posi units, with the same spline axels, can be interchanged. Initially I was thinking that unit was maybe mismarked, if they are not interchangable.

And was thinking that wouldn't it be more likely for an 86 SS Monte Auburn posi carrier, with 3.73 gears be more likely to have come out of an Aussie 9 bolt rear, rather than a 10 bolt rear, since aren't the 9 bolt rears supposed to be the high perfomance stronger rears?
Are the 9 bolt and 10 bolt posi carriers interchangable?

I just bought an 84 3.73 posi rear two weeks ago, but this carrier looked so much heavier than the 84 unit I bought. Plus that unit needs spider gears, which I scored for free. I was hoping I could put this Auburn posi 3.73 carrier and gears in the 86 9 bolt 2.77 rear I have that I was pretty much going to throw away. If this Auburn posi unit will fit in that rear, then I will be able to take a junk Aussie rear and turn her into gold, for under $200, (cost of new center pin, calipers, brake hoses and rear fluid)

The part is labeled:
86 SS Monte Carlo,
out of 7.5" 10 Bolt
Posi, 7.625 3.73 gears
fits aussie rear
*it is an Auburn posi carrier

Jegs sells Auburn Posi Carriers and lists them as fitting F & G cars, s-truck, MOnza, Vega, Nova, M-van and all GM "B" cars with 7.625 rear end
10-bolt 7.5 & 7.625, 26 Spline carriers
I don't know what letter body style Monte Carlo's are considered, but thought that they might be G cars, but thought that the carrier would fit in either the 10 bolt or 9 bolt rears I have, when compared to the information listed by jegs.
That would suck if the Montes, had 8.5 rears and I can't use it like I thought.

Hope someone can shed some light on this one.
Be cool!
"TEACH"

 

I am going to take a crack at this and say, the monte's had an 8.5 inch rear. As far as i know of the 9 bolt was not an option for monte's, and the insides of a 9 bolt and 10 bolt are not interchangable. Only the fluid is universal. Miles?
Anyone feel free to chime in..... SHAGGY

 

How do you tell or what or where do you measure to determine whether the rear is an 8.5 or a 7.5 or 7.625 rear?
Do you measure the diameter of the ring gear, from outside to outside at its widest point?
I so, I think the ring gear was either 7.5 or 7.625, when I tried measuring it that way. It wasn't the most accurate method, but I'm pretty sure the ring gear wasn't 8.5 in diameter.
Thanks starting insight into what I have and if I can put it in my 9 botl housing.
"TEACH"

 

Sorry, I was out of town at the NMCA race in Florida.

No, the 9 bolt carrier is not interchangable with a 10 bolt carrier, nor are anyother parts.

Can you take some pics of the gear set and carrier?
How many bolt holes on the ring gear? What thread and which direction? Is it a clutch style or a cone style carrier? What markings are stamped on the gear and carrier?

I don't know what size rear was in montes in the mid 80's, but I would guess it's a 7.5.

Miles
www.9bolt.com

 

Mike,
I hope that you did well racing. The weather has been off and on in Central PA, but no racing to be had for a few months.

The carrier is definitely an Auburn unit. It is a heavy piece, with only one window to the spider gears inside. I have read that the pinion shaft diameter is different from a 10 bolt to a 9 bolt rear, though I haven't measured it yet with my venier dial caliper.
I can take some picts of it and send them to you.
I am just on at the beginning stages of learning the terminology and basics of rear ends, though I have mastered rebuilding engines, timing, carbs, body work & painting. The rear end and set up of one, is one the last frontiers I have to explore, so please be patient and thorough in your responses.
I will do my homework and get back to you.
Thanks and Be Cool!
"TEACH"

 

Absolutely nothing will interchange between a 9-bolt and a 10-bolt. They are completely different designs: the 10-bolt uses C-clips to retain the axles, and the 9-bolt uses a bolt-on bearing retainer; the ring in a 10-bolt is 7½" or 7.6" or 7-5/8", whatever you want to call it, and the 9-bolt is 7.75"; etc.

The MC SS had the same kind and size of 10-bolt rear as a Camaro. The housing and axles of course won't interchange, but the internals will. Unfortunately your stuff is probably for 26-spline axles, which are considerably weaker than the later 28-spline ones. Ask me how I know about the splines... In any case, the MC is a G body; and like the catalog says, that kind of rear is used in late 70s on up G cars, 82 up F cars, 80s B cars (Caprice and its cousins), A cars (Malibu), Monza, S trucks, etc. It's a very common unit.

Like the other post said, it is totally incompatible with the "Aussie rear", which is a 9-bolt. That phrase in the guys ad is a red herring, as the part in question is in no way connected with the Australian Borg-Warner unit.

Maybe you should come up with a 10-bolt housing, with good 26-spline axles in it, to put that Auburn into; it shouldn't be too hard or expensive to do that.