another couple of comments on 'posi'

A lot of people whom talk about 'posi' don't actually know what is what. ( not the guys above, they were on the $$ )

Just a couple of notes, ( some are rehash-ing the above )

a true pozi means the two axles are 'positively' locked together. This is great for the track, but irritating and downright undesirable on the road. I understand they audibally 'CLUNK' anytime you take a turn. Dunno, never had a true pozi...

limited slip: several types of limited slip exist... some use 'cones' others use clutch disc stacks. This type will keep the axles locked to a preset torque load, after which they will 'slip', allowing the wheels to turn at different speeds. When driving in a straight line, as on a hiway, the lube tends to sling out of the discs, and they 'lock'. So, the next time you take a turn the rear end will audibally CLUNK as the discs break free. Sometimes, they will clunk repeatedly through the duration of a long, shallow turn. It also FEELS like a flat tire while doing this. You have to put special additive in the gear lube, but it only helps some. Better for the hiway, not as good for the track. It is a good compromise for the street.

now for the 'however':
pozi and limited slip wear the tires ( to the inside ) reduce gas milage ( on the street ) and increase the potential for the rear end to 'fishtail', PARTICULARLY on wet road.

'open' rear differential, is what the automotive mfg's prefer for stock application. It allows the tires to wear better, and gives overall performance improvement to the daily driver.

I put a clutch type limited slip under my 78, and the only time it was useful was the few times I pulled off to the shoulder, and one tire was in the mud. I'd certainly have been stuck without the limited slip. Overall, I hated it. It wore out my Hoosiers quickly, and the car fishtailed WORSE after I installed it, and I had the misconception that it would help prevent the fishtailing.

I have since swapped it out to an open diff, and am much happier.