Open or Posi?

[albertarose]

I dunno about that ..Mie left 2 patches of rubber for a hundred feet and when it shifted to second at 5500 rpm I was deffinatly going faster than 20 mph LOL :rndll:

Originally Posted by eedgell

I think the "posi" is short for positraction, which means positive traction to both wheels. If you lift one wheel off the ground, and the posi unit is in good shape, you should not be able to turn the wheel that is off the ground. The posi works on centrifugal force. At about twenty miles per hour the clutch system disengages, and then operates like a one legger does. The best way to tell is to pull the cover, but the test I listed above works well if the unit is working properly.

[Morgsie]

Originally Posted by albertarose

I dunno about that ..Mie left 2 patches of rubber for a hundred feet and when it shifted to second at 5500 rpm I was deffinatly going faster than 20 mph LOL :rndll:

No, eedgell is right. Try punching it at highway speeds, it will not engage the other wheel. My Impala has an "original" posi, if you want to call it that. Regardless of speed power is transfered to both wheels. That means passing people on icy/wet roads at highway speeds can be pretty exciting if you don't know what to expect. This is why they developed the "locker"; it will not engage at fast speeds which means you wont be doing dough nuts into the ditch or other people.

[LONGHAIR]

The posi works on centrifugal force. At about twenty miles per hour the clutch system disengages, and then operates like a one legger does. The best way to tell is to pull the cover, but the test I listed above works well if the unit is working properly.

This is why they developed the "locker"; it will not engage at fast speeds which means you wont be doing dough nuts into the ditch or other people.

The diff that you guys are talking about is GM's Gov-Lock. They were not available until '73...as replacement for the original "posi-traction". "Posi" is a shortened/slang and often mis-understood/mis-used term. The Gov-Lock was supposed to be safer and more forgiving, but they are not as strong. The little clock-works guts will come apart if you have more power and/or bigger tires.
A "locker" is a totally different animal.
This is the best write-up I have seen...

Gov-lock(G/L) Used by General Motors in 73 & newer trucks that came with an option locking / limited slip differential. It was used in 7.5", 7.625", 8.5", 8.6", 8.875" 12 bolt truck, 9.5", 10.5", and now in the new 11.5" differentials. The smaller designs are fairly weak and the 8.5" and 12 bolt truck designs are especially weak. The 9.5" and 10.5" 14T units are fairly strong and will hold up well to towing and moderate abuse. The Gov-Lock is designed to act as an open differential during normal driving with no force being applied to clutches. This fact that no force is applied to the clutches keeps the clutches from chattering during normal every day driving. When either wheel slips and spins approximately 100 rpm faster than the other a governor assembly senses the difference in speed and activates a ramp system. The ramp system causes the clutches to engage and transfer power to the wheel with traction. One other feature of the Gov-Lock is that it will not engage at vehicle speed above 30 mph. This no lock-up feature keeps the vehicle more stable at higher speeds where both wheels spinning could cause an inexperienced driver to spin out or slide off of the road. This is a great design in theory and works as designed in a stock vehicle that is not abused. The problem is that most of us modify our trucks and many of us abuse them. When this unit is asked to deliver under extreme conditions it tends to self-destruct. The force generated by the ramp system that is used to lock-up the clutches works well, except that same force has to be contained by the case and the case is not always up to the job. (factory)