can you tell just by looking at a carrier unit if it is a posi unit or not? looking with your hands is also allowed. what if it is in a rear end?

thanks

 

Easiest way is if you are lucky and see the posi tag still bolted on.

 

whats a posi tag? also is there anyway to tell condition of posi unit. would a posi unit from a 91 firebird likely be in a good or bad condition

 

jack up the rear and spin the tires... if they spin the same direction you have a posi

 

G80 RPO code

 

pull the cover and look, it's the only 100% sure way to know

 

how would the carrier itself look if it is a posi, i dont know what it would have if its open or posi.

 

There are limited slip rearends, cone type lockers, ratchets, lockers,spools and maybe some others that are often refferred to as "posi" units. A "posi" as I recall, is what GM called their limited slips.
From outside the car.
1. jack it up and spin the rear tires, if they go in the same direction chances are it's a posi.
2.jack up one side of the car, if you can't spin the tire thats in the air, chances are, it's a posi.
3. do a burnout, if both tires leave rubber marks, chances are it's a posi.
4. find the tag as has been mentioned.
**none of the above guarantees you have a"posi", in fact none of the above can happen and you may have a worn out"posi".

If you take the rearend cover off of the car, or pull the banjo, if it's a Ford 9" style you need to look at the center section. Let's assume it's a GM style unit that loads from the rear. Where the axle "c"clips are located. What you would see in that location in a non-posi unit is simply 4 spider gears, and a pin that runs down the center that locates 2 of those gears. This is usually located by a small bolt that ends up breaking off in the carrier itself and causes it's own set of problems. This bolt screws in from the unit, opposite the ring gear. That's all that is there.
If you look at that and see springs, clutches, sprags, virtually anything else, then it is some form of limited slip unit, or. It may also be a spool, which is a solid piece that drives both axles, these are used in race cars and use the bearings to retain the axles, these should never be used in a street car, so I really doubt you have one of these.
Once you decide what you have, the best place that I've found is:
www.reiderracing.com
These guys are very knowledgable and have parts for most rears in stock.
http://www.reiderracing.com/rtech_diffs.htm
should cover most of your questions