I Own 3 Cadillac Coupe Deviles An Looking To Up Grade Gears An Posi Or Other Wise Knowen As Limited Slip Been Trying To Find Out If The Caddy Is 8.5 Or 8.2 But Axle Bolt Are 5 Of 5" As In Capicre Cars An Truck 2x4 A Friend Has A Couple Rears Own Was In A Grand Prix With V 6 An Limited Slip An Says 3.73 Buy Smaping On The Axle Tube Also A Rear Out Of An 78 Buick Was A Standard Shift 3 Speed On The Floor Limited Slip With 3.42 Ratio The One Coupe Going To Replace The Engine With A 472 Cub. In. An The Other I'm Converting The 4.1 Liter To A 4.5 Liter By Replacing The Cylinder Sleeves From A Tranvers 4.5 Out A 1990 Caddy. I Found A Caprice Rear From A Cop Car Limited Slip But Yard Wants $375.00 For It To Much An Being A Cop Car Rear Fear Be Abused Alot. So Any Help Be Greatful.

what year are the caddy's?

 

caddy years

ones a 1982 others a 1983 an other is a 1984 all coupe devilles

 

8.2 or 8.5

I'm not to sure about you caddy, but I had the same problem for my nova I didn't know what rear end it had an 8.2 or 8.5. I called a transmission shop and they said take the differential cover off, if the ring gear has a 9/16 bolt its a 8.2 and if it has a 3/4 bolt on the ring gear it's the stronger 8.5. My nova ended up having the 8.5 10 bolt rear end.

 

You can tell by looking at the housing check this site out.
http://www.oldsmobility.com/10bolt-tech.htm

 

Those years wouldn't have had an 8.2" rear end. Those were discontinued in the early '70s. You need to watch out for the weaker 7.5" unit, which is also pictured at the aforementioned site. Notice the little "fangs" at 5:00 and 7:00 on the 7.5" housing. Stay away from things with fangs.