Hi
I have an aluminum center section and new 3.55 gears and need a posi unit to complete this piece for my 8-3/4 489 case rear end. What is one of the better posi units that I should be looking to get, Its a 440 blown duster that is only street driven and I get on it from time to time.

The best of the factory or OEM units is the early disc clutch pack unit. It locks up well and is rebuildable. The later Auburn unit uses cone clutches and is difficult to rebuild, later ones may be impossible. Among the aftermarket limited slips the torsion type [ uses worm gears ] is very street friendly and reasonably strong. The Detroit Locker is as strong as anything short of a spool, but can be grabby.

get a powerlock sure grip from a 42 case (68 & earlier) 8&3/4 (several hundred bucks or less) and throw in a new set of clutches which are cheap maybe ~50 or so and you have a very good base to work with. EDIT or from a 741 case, just the sure grip not the (741) gears/pig

Iam running a Detroit true trac in my 8 3/4 i love it and put a ton of street miles and some .

Eaton Detroit Locker is the strongest thing out there next to a spool. But they're not the cheapest thing out there either.

That depends on what you're using your car for mainly. One thing to keep in mind is, The tighter your axles are sprung, the better traction you have in the straights, but increased tire wear everywhere else. This is desireable if you're drag racing. Not recommended for the street.

1) OEM uses clutches to "lock-up" the axles. Its the least tightly sprung and doesn't last as long as an Auburn "Cone Type"

2) Auburn, uses "Cones" to lock up the axles. Its sprung up tighter than the OEM and lasts longer. Its drawback is, its NON-REBUILDABLE. Although, Auburn has an exchange program where they'll take your worn unit and give you credit towards a new one.

With the above 2 units you cant go wrong, especially on the street.

I haven't tried using a Locking unit.

Steer clear of using a spool on the street. Tire wear is horrible, wheels "Chirp" and Hop while cornering, and if your tires are really wide or sticky, make sure you have a spare set of axles.

Any cone type is absolute TRASH , this is going behind a blown 440 , you'll soon find the weak link , the gear teeth , if you have any kind of traction and boost .

Dr. diff has new clutch types , but I'd look and the othersmentioned also ... EXPECT that POS auburn unit ...

Just to clarify, the early Auburn units were OEM. Chrysler used both disc and cone units as original equipment. The Auburn [ cone clutch ]was used starting in either very late '60s or early '70s. In so far as I know these were only used in 489 case units. Earlier 741 & 742 cases used the disc type clutches. Either one can be used in either case so long as you use the correct side bearings. Later Auburn units are an aftermarket design. If I were going to buy an aftermarket limited slip, I think I would go with a Torsen type diff. at least for street or autocross use. No doubt the aluminum case is the strongest of the 8 3/4 rears, but if you have a LOT of torque and grip the Dana 60 is still the gold standard.

I use a Powertrax Lockright. Just wear earplugs so you don't hear the knock-knock around slow turning corners or the cops coming after you smoked the tires real good.

The Dana Powerlock (the early disc-clutch style) is nice because it's designed to apply more force to the clutch pack when you apply more torque with your right foot. In practice, when driving slowly around corners the clutches slip but if you blip the throttle during a turn the inside tire squeals. That's been my experience using them in Dana 60's and 8-3/4's.