Does anyone really know on the front Diff?

[Gordy]

With the autotrac 4wd system if the FRONT is up in the air, tires off the ground, and the vehicle is in 2WD, and PARK. Are the FRONT tires suppose to turn freely by hand? If only ONE FRONT tire is off the ground should it still spin freely by hand. Its a 2001 Tahoe LS. Does not have the G80 it has the GT4 3.73 which is the rear Diff anyway.

I have found out that the FRONT drive shaft should NOT spin freely in park, and 2wd on models 2005, and older Autotracs.


Sorry if I'm beating a dead horse but my last "Dumb question thread" I did not really think anyone was completely sure that responded. Kept reverting to the G80 not being able to spin.


Gordy

 

[Jay]

There are two parts to this situation: axle lock, and transfer case engagement. The front CV shafts ALWAYS turn no matter what mode you are in.

While in 2wd the front axle is disengaged (or is supposed to be!). Just off the passenger side of the diff you will see a motor assembly, this is what engages the passenger side axle to the differential, locking the front end together when you put it in Auto4wd or either 4wd mode. In Auto4wd the front axle is locked and turning with the wheels, but the front driveshaft should not be locked at the tcase since the clutchpack has to be engaged (commanded by PCM). In 4wd high or low, there is a mechanical engagement that overrides the clutchpack that fully engages the front driveshaft for a true 50/50 front/rear torque split.

Our 8.25" IFS front diff is a purely open differential... no clutch packs and, as many off-roaders have discovered, NO locker is available. So the spider gears are free to turn without resistance. This also means you will get a one-wheeler in the front end in slippery or off-camber (one tire off ground) situations.

This is why i like the stabilitrak system in these trucks. Even with stabilitrak off, the wheel-brake traction control is active, essentially giving you front and rear lockers as any free-spinning wheel will get individually braked, sending power to other wheels.

With the wheel-brake system, lockers are not necessary and would rarely get used if they were there anyway. This is a good system for slippery roads or very mild off-roading. If you spend a lot of time in deep mud, lockers are superior simply because mud will eat the brakes in no time. Plus the wheel brake strategy consumes a lot of power.

Oops, got a little off topic. Hope this helps.