Just to see what makes 'em work, I just disassembled the old Gov-Loc from my S-Jimmy. It's actually a pretty slick contraption! A fine-toothed gear on one end of the diff will start a small, weighted governor spinning if the 2 axles start to rotate at different speeds. The governor is spring loaded, so that it won't engage the posi until the speed difference between the 2 axles is approximately 100 RPM (so you don't fight the posi in normal cornering). Once that RPM is reached, a pair of cogs swings outward and engage against another governor-type device (one of the cogs works for forward motion, the other for reverse). This stops the first governor from spinning, which stops the fine-toothed gear on the end of the shaft from spinning. The fine-toothed gear has a wave-shaped back, which normally fits into another wave shaped section on the side gear. When the governor forces the fine-toothed gear to stop rotating, the two wave-shaped sections of the gears start sliding against each other, which forces the side gear to move towards the center of the diff. As it moves, it applies force to the clutch packs, connecting the two side gears together via friction.
Now, remember the 2nd governor-type device? It is also spring loaded, and once the wheels are spinning at about 30 MPH, it swings out of the way and disables the ability of the first governor to lock against it.
So in normal driving, there is nearly zero preload on the clutch packs (there's a small wave washer that applies just enough pressure to keep the clutches from rattling around when the posi isn't engaged), which means your diff behaves as if it were open.
When a wheel starts slipping (below 30 MPH)the posi engages quickly and firmly, providing drive to both wheels.
Over 30 MPH, the posi can't engage, so it won't create any driving quirks at speed.
It's a pretty **** nifty piece of engineering! /forums/images/graemlins/thumb.gif But the trick to making one live is to be easy on the throttle. Doing stuff like full-throttle bursts from a standstill in the mud, or on ice/snow, will cause a tremendous shock load as the clutches are slammed home and everything locks together. That's when gov-loc-go-boom! /forums/images/graemlins/wink.gif
All of the other clutch type posis that I can think of work very differently. They typically have a couple of mongo springs inside, that pre-load the clutches against the side gears. This means that the clutch packs are always trying to keep the axles from rotating at different speeds. As you go around a corner, the traction of the tires must overcome the friction of the clutch packs before the diff will actually allow differentiation. This is the type of posi that will be most likely to chatter. Posi additives modify the friction coefficient of the clutches so that they can operate more smoothly when cornering. Since the gov-loc doesn't engage the clutches until they're needed, it doesn't need the additive.
