[Willy1950]

I was looking at a rear-end yesterday and was told it came out of a Sunfire I believe. It is 48" roughly plate to plate. Back cover looks like a 8.5. Told it was a posi. So I marked the drum and Shaft. Spun drum 1 full revolution and the drive did 1 and a bit. Also the other side didn't turn?
Can someone help me with this.
Guy wants 400cdn.
Thanks

 

[big gear head]

If one tire turns and the other one is completely still then turn it 2 turns while watching the drive shaft.

 

[ericnova72]

Also doesn't sound like it has a posi, or if it does it is burnt up. Any positraction unit would not allow just one wheel to turn, with the exception of the Gov-Loc, which you don't want anyway because it is really weak....they call if the Gov-Bomb or the Grenade-Loc....or my favorite, the Koo-Koo Clock Posi.

Also sounds lke really poor rear gear, 2.41, 2.56, 2.73 at best

Sunfire, that's the Buick version of the Chevrolet Monza...H-body, derivative of the Vega.
It won't be an 8.5" unless someone narrowed one from some other vehicle, and welded on new mounts and such....hard to do wth the Monza having cast in center torque arm provisions on the cast centersection. H-body's all had a version of the 7.5" unless very early, then a 6.75". None ever had a stock 8.5"
48" plate-to-plate is not how most measure a rear axle, better to give Wheel mount-to-whell mount surface dimension....but 48" plate-to-plate sounds right close to 54" wheel-to-wheel....which is Vega/Monza and S-10 truck width.

Look here for pictures of easy casting identifiers for the difference between 8.5", 8.2", and 7.5"

NovaResource - Nova Rear Axle Codes

Probably not a Posi, dude is likely fibbing trying to make a sale, so far doubled shaft count shows really crummy gear ratio, width really looks like crummy 7.5" rear....price is $300 too high.
If he is serious he'll let you pull the rear cover off and look.

 

[Willy1950]

Also doesn't sound like it has a posi, or if it does it is burnt up. Any positraction unit would not all just one wheel to turn, with the exception of the Gov-Loc, which you don't want anyway because it is really weak....they call if the Gov-Bomb or the Grenade-Loc....or my favorite, the Koo-Koo Clock Posi.

Also sounds lke really poor rear gear, 2.41, 2.56, 2.73 at best

Sunfire, that's the Buick version of the Chevrolet Monza...H-body, derivative of the Vega.
It won't be an 8.5" unless someone narrowed one from some other vehicle, and welded on new mounts and such....hard to do wth the Monza having cast in center torque arm provisions on the cast centersection. H-body's all had a version of the 7.5" unless very early, then a 6.75". None ever had a stock 8.5"
48" plate-to-plate is not how most measure a rear axle, better to give Wheel mount-to-whell mount surface dimension....but 48" plate-to-plate sounds right close to 54" wheel-to-wheel....which is Vega/Monza and S-10 truck width.

Look here for pictures of easy casting identifiers for the difference between 8.5", 8.2", and 7.5"

NovaResource - Nova Rear Axle Codes

Probably not a Posi, dude is likely fibbing trying to make a sale, so far doubled shaft count shows really crummy gear ratio, width really looks like crummy 7.5" rear....price is $300 too high.
If he is serious he'll let you pull the rear cover off and look.

Here is a pic of rear-end. It also has 2" studs on it?

 

[stuarta]

Here is a pic of rear-end. It also has 2" studs on it? View attachment 526918

Yank the cover and count teeth.

 

[ericnova72]

Here is a pic of rear-end. It also has 2" studs on it? View attachment 526918

That's a weak-suck 7.5" 10-bolt, as witnessed by the cast "fangs" at 5 o'clock and 7 o'clock below the cover face

 

[big gear head]

There's no way that's a $400 rear end. It's the 7.5 and when you turned one axle and the other one didn't turn then it's either a standard differential or a worn out limited slip.

 

[Yeeha]

Suggest you go on Amazon and buy a USED copy of this book before wasting money getting the wrong rear end. Will pay for itself.

 

[curtis73]

Yup. 7.5" Great for low hp, low weight.

Highly doubtful it's a gov-lock in a 7.5, but possible. Most likely either a cone (auburn style) or clutch (eaton style) posi if it is one. Only way to tell is to pull the cover, but honestly, that's a $50 rear end at best. Maybe $75CDN

Gov-lock could act like an open diff by just spinning the wheel. It's open until a little centrifugal clockspring engages the clutches to make it limited slip. Just slowly turning by hand wouldn't engage the posi part. So, it could be a posi if it's the gov-lock style. Gov-locks are also not a bad thing. Everyone on the internet talks about how awful they are... but they just aren't. The bad reputation came from 40 years ago when all the drag racers were looking for cheap posi rears for the strip. They would grab a 12 bolt out of a truck with a gov-lock, then promptly take it to the strip. They would launch with slicks and 500 hp instantly liquefying one tire. Then a split second later, the clockspring engaged the clutches... after one wheel was already spinning with the entire torque of the engine behind it. It engaged the posi and WHAM.

On the street, it's a wonderful thing. Open diff 90% of the time until you need it. I have pulled apart gov-locks from duallys and step vans with 500k on them and the clutches look brand new. Don't listen to the intarwebs tell you about how awful gov-locks are. They aren't. They're fantastic. Just don't use them for drag racing with big torque and you'll be fine.

 

[curtis73]

I have tested the limits of many 7.5" rears. My buddy put a stock LS1/T56 in an 84 firebird with a 7.5/7.625 rear. With the all-season rubber, it was fine, but then he got some sticky rubber to autocross it. The very first time he grabbed 2nd at WOT, it ejected the carrier out the cover. Ripped the casting apart, tore out the bearing studs with a big chunk of iron.

 

[joe_padavano]

Sunfire, that's the Buick version of the Chevrolet Monza...H-body, derivative of the Vega.

Pontiac, actually. The Buford H-body was the Skyhawk.

 

[ericnova72]

Pontiac, actually. The Buford H-body was the Skyhawk.

Thanks, Joe, you're right.
GM changed names on all those H-bodies when they added the Monza platform on top of keeping the Vega in the line-up and the names got all lost on the fog of time for me. Sunfire, Starfire, Skyhawk.

 

[Chad & Karen]

A little off topic, but it is just baffling to me that g.m./ford/ mopar built the smaller ring gear rear ends.
I mean how much are you saving in metal to justify engineering, tooling, stocking, cataloging ,building a different center chunk to drop into the same cars .
I mean was g.m. saving enough money building a 10 bolt and a 12 bolt for the same car?
or a 7.5" and a 8.2/8.5"
Same with ford and mopar. just seems like a lot of effort and warehouse space for what ever little metal the smaller center chunk saved them. over just building one unit and calling it good. As this was done decades before the just in time ordering production line parts supplying was a thing.