Are Open Differentials That Bad?

[kingcolbert83]

What is the true knock on open differentials. Everybody wants posi traction, heck even me but I dont know why? I understand the concept of sending power to both wheels but does it even matter if you are not getting the power to the ground with traction anyway? I would think open would be better for suited depending on where you live. We hardly get any snow here in columbus, ga and I havent had a problem driving it in the rain thus far.

From my reading an open differential actually takes less power to turn/use which I would think would be better because you have less power loss through the drive train right? Just curious before I make a decision on a posi unit. I am truly thinking ring gear spacer, 3.73's, and a street radial(or slick) on that one leg. I have actually beaten a few cars that had posi vs my open.

 

[pontiacgp]

you make some good points and valid ones....I ran a posi till it blew up and for now I have an open rear end. I can sit there and burn up one tire if I want but for normal driving on dry or wet roads it is fine and although I don't notice any gas mileage improvement you are right that an open rear end does turn easier going around corners..for planting the power down and for pushing the car around corners a posi is a required item tho so most go for a posi

 

[JBreu]

For a daily drive an open differential is ok...But for a street rod or a street/strip car with some power, they are worthless.....Better traction with both wheels getting the power.....The "One Wheel Peel" doesn't impress anyone...Only saying 8)

 

[MD13ailey]

and if you put a slick on the one leg the other should spin. path of least resistance

 

[Bonnewagon]

If the car is pointing totally straight ahead, power is sent to both wheels equally because the differential can't rotate. However as soon as the car turns, or one tire loses traction, the differential does it's job and rotates in reaction to the unequal axle speeds. The posi prevents that by clamping the differential clutches with heavy springs maintaining traction to both wheels. On a turn, the posi clutches slip and allow the differential to operate normally. Bottom line- on a pure street car, not driven in snow, you won't miss posi, just watch out for that Georgia mud.

 

[pontiacgp]

If the car is pointing totally straight ahead, power is sent to both wheels equally because the differential can't rotate. However as soon as the car turns, or one tire loses traction, the differential does it's job and rotates in reaction to the unequal axle speeds. The posi prevents that by clamping the differential clutches with heavy springs maintaining traction to both wheels. On a turn, the posi clutches slip and allow the differential to operate normally. Bottom line- on a pure street car, not driven in snow, you won't miss posi, just watch out for that Georgia mud.

on an auburn there is constant pressure at all time and the wheels have to over take the pressure when turning...I had a b*tch of a time moving my rear end around (the one on the car) when I was doing the frame off. That posi did not like me turning that rear end...

 

[G_Body_Enthusiast]

i'm eyeballing a detroit truetrac differential. it's a torque biasing diff so it transfers more power to the wheel with more traction minus the slipping clutches and other stuff like that. no maintenance required, it's all made of gears. it's also one of the cheapest diffs i've seen, about 375 bucks for 26 or 28 spline, series 2 or 3.

i have considered sticking with an open diff, but the car is taking a slightly new direction so i think some sort of posi is needed. and i really like driving around corners and curves and the streets are full of them.

 

[Bonnewagon]

Yeah, it takes about 400 ft lbs of torque to break loose the clutches on a GM posi. Easy for a car to do, but almost impossible for a human by hand. I like the 7.5" S-10 type part-time posi. It freewheels at normal driving until one wheel slips. Then it winds up and goes BANG into lockup mode. There is a centrifical weight on the case that needs X amount of force to move it and engage the posi. It is great in the snow and you forget it's there in normal driving.

 

[megaladon6]

remember, what most people are calling a Posi, is actually a Limited Slip Differential. all factory "posi" rears are actually LSD'. when in a turn, the outside tire is allowed to go faster than the inside, just like an open diff, but it will prevent tire spin in a launch. well, uneven spin! you can still roast both tires.
then there's the true posi or "spool" diffs. those effectively "lock" the axles together and will always send the torque evenly to both tires.

 

[othtim]

Is going to a posi unit on a 7.5 rear end going to significantly shorten it's life? Lets say you were running around 250-300whp, with no more than 275 street radials.