[darbikrash]

My car is a '69 base 400, w/Turbo 400. As it is factory A/C, it should have 3.23 posi. The rpm at freeway speeds lead me to believe the ratio is not 3.23, and I wonder if this rear end is actually a 8.5 due to the ears on the bottom edge.

The tag references "limited slip" lubricant only. I guess I can pull the cover and measure the ring gear diameter and tooth count, but does this look like a factory 8.2?

['ol Pinion head]

most common housing style of the '71-72 8.5 A-body rear, but someone has installed the round cover off a c-clip axle 8.5 rear. should have a cutout style cover & proper gasket. Stronger rearend than any 8.2 rear due to more pinion support.

[north]

Here is an example of a stock 69 diff

[darbikrash]

Thanks for the replies. So then I have a 8.5 from a later model A body. I have confirmed it has posi, and using chalk marks on the driveshaft I estimate a 3.08 final drive ratio. I think I'd like to pull the cover for a closer inspection and tooth count. Is there a source for the correct cover, and what lube would be recommended?

It probably also makes sense to get some casting numbers to identify the exact year of the rear end, where would these numbers be located?

The car is new to me this past week, so I'm just going over it trying to understand what I have.

Here is a pic:

[north]

Nice car, I had one the same color scheme. Car seems to sit too high in back. Maybe the spring perches are different than the stock diff

[darbikrash]

Good eye. My guess is has something to do with this, likely they had problems clearing the exhaust which is wrapped around the read end, so they raised it up to clear rather than correct the exhaust placement.

['ol Pinion head]

Darbi, The rear is def a '71-72 8.5 A-body. That particular casting center housing was used for two years, & shares same casting number. Have been building HD 8.5 A-body rears for the last 25 years, currently have over two dozen of that particular 8.5 A-body housing in the racks.

When you drain the r/e grease (80/90 w small bottle of GM or Ford Limited Slip additive), take a look at the posi carrier... might post a pic showIng a partial view of the passenger side end of the posi carrier. For many years, several of us rebuilt this style rear with the later & more common #8 or #9 c-clip side gear Limited Slip carriers, and properly rebuilt, set them up with a nice used or new ring & pinion in the bolt-in axle 8.5 rears. The original style "S" spring 8.5 posi carriers for bolt-in axle use aren't nearly as common, as the c-clip version, & its possible your rear began life life most as single track rear, & was assembled at some time with a posi carrier. Need a nice used cutout style cover, feel free and drop me a PM, should be able to grab one.

[darbikrash]

Originally Posted by 'ol Pinion head

When you drain the r/e grease (80/90 w small bottle of GM or Ford Limited Slip additive), take a look at the posi carrier... might post a pic showIng a partial view of the passenger side end of the posi carrier. For many years, several of us rebuilt this style rear with the later & more common #8 or #9 c-clip side gear Limited Slip carriers, and properly rebuilt, set them up with a nice used or new ring & pinion in the bolt-in axle 8.5 rears. The original style "S" spring 8.5 posi carriers for bolt-in axle use aren't nearly as common, as the c-clip version, & its possible your rear began life life most as single track rear, & was assembled at some time with a posi carrier. Need a nice used cutout style cover, feel free and drop me a PM, should be able to grab one.

Here are some shots of the rear differential, a tooth count shows this to be a 3.23 final drive ratio.