Q: What is posi?
A: Posi is a rear differential unit that keeps power applied to both wheels as consistantly as possible, as opposed to just one wheel in an "open" rear. In general, a posi unit will "lock up" both wheels under power but with reduced power (in a corner) the axels are allowed to rotate independantly and thus make going around corners possible without taking all the rubber off your tires. Posi is short for posi-traction, or "positive traction".
Q: What is a spool?
A: A spool is a rear diff. unit that is locked all the time. Period.
Q: What is limited slip?
A: Limited slip is posi, just another name for the same thing. Keep reading.
Q: What about the "Detroit Locker" ?
A: Yes another name for the same thing, although we think the mechanism may be slightly different.
Q: Are there different types of posi?
A: Yes, but they all do the same thing. There are "cone" types, "clutch" types, etc. There are also differnt leves of "strength" which determines how often a posi unit is lokely to be locked up. See next question.
Q: What about chirping tires around corners?
A: Different posi units have different spring loads, some are more stiff (stronger) than others and thus stay lock up more often. e.g. the Auburn PRO unit vs. the standard Auburn unit.
Q: Was the posi in the '70's Vettes special?
A: No. It was standard limited slip (posi). Some people just think it's different because the Vette has independant rear suspension.
Q: What are some other names for posi?
A: This is the hardest question to answer because it's hard to trace the origins of the "nicknames" from various manufacturers.
GM = Limited Slip and maybe Posi-Traction

Ford = Traction-Loc and maybe Detroit Locker

Chrysler = Sure Grip
 
 
 

From Mike Donovan's Monte Carlo Page
 

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