what is the so called POSI on a car?

Question

i know its the rear end but wat part of the rear end? wats the difference between 12 bolt , 10 bolt & any other bolts there are?

Answer 1

posi meens that both wheels lock up not just one as far as bolts as u call them diffent gear ratios and size of pumpkin

Answer 2

All of those terms refer to GM products. Posi is short for Positraction. Other variations of it are called a Locking Differential or "locker". The difference is that power is supplied to both axels exiting the differential that put power to the wheels. You can have a posi or locking front and rear differential if you have a 4x4.

This comes in handy for a few situations. First being offroading where one wheel might lose traction in mud or come off the ground. Or on a race track where the power of the engine breaks a tire loose and spins in one spot.

With a standard differential setup, the tire that spins the most freely will receive all the power and continue to spin regardless if it has traction or not.

On a posi or locking setup, both sides receive equal power. Since generally at least one tire is touching the ground or has the most resistence, you will get maximum power to the ground instead of wasted power in spinning a wheel that has no traction.

Situations where Posi or Locking diffs are no good are tight turns where the inner tire wants to spin at a higher rate than the outer one. This will cause the diff to either disengange with a loud pop, snap an axel or break loose the inner tire so it can spin at the same rate the outer one is. This also causes the rear ends of vehicles driving on ice to spin outwards much easier.

On the 2nd part of your question:

GM manufactures several variations of rear ends.

10-bolt
12-bolt
14-bolt

This refers to the number of bolts holding on the differential cover that faces to the rear of the vehicle.

Ford has two that are quite popular as well but they go off of a size rating like the Ford 7.5, 8.8, 9", 9.75", 10.25"

Dodge tended to use mainly Dana Spicer, they made several different types as well and some of the Dana's were also used on some Ford and GM vehicles. A few Dana rears are the 28, 30(mostly fronts), 35, 44, 50, 60, 70, 80

The larger the rear end, the higher its capacity to hold up weight, tow and transfer power to the ground. If you have a 600 horsepower car, you couldnt use a puny little Ford 7.5" rear. It would come apart.

Answer 3

posi is whether or not both wheels will spin. the bolt amount usually refers to the number of bolts that hold the backing cover on and that helps identify what diff is in the car

Answer 4

POSI makes the differential gears turn together at the same time. So both tires turn not just one drive tire. Watch the court room scene toward the end of the movie "My Cousin Vinny" and it explains this also.