fazm83 said:
Limited slip differentials will spin the opposite way, and a posi rear will spin the same direction.
There seems to be alot of miscinceptions about Diffs so here we go, differentials 101:
There are 3 types of differentials:
Open rears
Limited Slips
Spools a/k/a Locked rears
Limited slip and Posi are the same thing (and BTW altough "posi" has become a generic term for limited slip like "Coke" is for cola, it is actually a Chevy term. Fords have Traction-lok). Limted Slip rears use clutches, though some like a Detriot Locker use a ratchet assembly, to send power to the wheel with traction. Since normally both wheels have equal traction, when you light up the tires on a limited slip equipped car both tires will spin.
An open rear sends the power to the wheel with less restistence. which is why you see cars stuck with one tire on snow spinning like crazy and one tire on dry pavement not moving.
Lastly are Spools or "locked rears" which are used excuslively in Drag Racing. Technically Spools are not differentials. Spools have no spider gears, just a solid piece of metal with the Ring Gear Bolted to it and splines for the Axles. With Spools both tires spin at the same speed all the time regardless od conditions. This makes turning difficult since when you turn the outside wheel covers more ground then the inside and therefore has to spin faster.(Which is why cars have differentials in the first place,to allow the wheels to spin at DIFFerent speeds.) Because of this Spools are no good for street use.
Normally when on a lift if you spin the tire on a car with an open rear they ill spin in the opposite direction. With a posi the will spin in the same direction and of course the same is true with a Spool. This is true probably 95% of the time, but it is not a 100% accurate way to detremine what type of Diff a car has. The only sure way is to pull off the cover and look at it.
As far as the 7.5 rear. My 1985 GT came with a 7.5 and it was junk. Maybe Ford has beefed it up since 1985 I don't know. i can tell you that I blew mine apart about 3 months after I got my car, then again about a year latter. I ended up swapping it for a 8.8 in 1987 (when the 5.0 came with 8.8) And remember back in 1985 my 5.0 Mustang GT had the same 210hp as your V6s. If I had a 7.5 equipped car I would probably swap it for an 8.8.