jmansouri

Sorry this will be long...
I have done some searches and come up with conflicting information on this subject, so i have done some real world tests and want to share and discuss this. I am trying to identify noise i believe is coming from the tcase/front driveline area. I believe might be caused by the tcase not disengaging the front driveshaft partially or completely.

(Should the front propeller shaft be free to turn by hand when parked in 2wd - ie not being driven by either the front diff or the tcase in 2wd mode)

So in 2wd i can lift the front of my 2001 2500 LS suburban up and rotate either the left or right front tire without the front drive shaft turning. when i actuate the auto 4wd mode i hear the actuator engage the front axle connect and then unless i have both front wheels in the air i can no longer rotate either wheel without rotating the drive shaft. so i know the front axle section is working correctly.

Now, a GM engineer told me that with the auto 4x4 tcase, when you select the auto function, the front axle locks up, but the tcase also sends some torque to the front prop shaft to get the ring gear rotating prior to the front axle connecting, so that all the components are rotating in the correct direction so the gears dont clash as they connect. makes sense if the front prop shaft is not turning. the left side axle shaft will drive the spider gears in the diff and the output will be in reverse on the right side (not the right cv axle...just the stub axle inside the diff housing).

ok, so after all that, my driveshaft is unable to be turned by hand with the car parked in 2wd, with the engine running or not. i checked with my brother who has a 2004 1500 LTZ and with his parked in 2wd you can rotate the front driveshaft fairly freely. i also checked another neighbor of mine who has a 2002 gmc suburban 2500 LT and his driveshaft is like mine...cant turn it in park 2wd.

So, is this a 1500/2500 difference? should you be able to turn the driveshaft by hand in park 2wd or not? i understand it may turn due to fluid and clutch friction but not be like its engaged...

thoughts?

trainwreck91

Could be a non responsive actuator. Many have had this issue. Either stuck in 4wd or not engaging 4wd

jmansouri

Well I am able to shift the tcase between ranges, I can get to 4 low etc so I know it's at least working somewhat. I'm hoping from some feedback from others with similar vehicles though.... Do your front driveshafts spin by hand when parked? What model do you have?

calwaterbear

Sorry, I have not been around here much lately. I have a 1997 2500 with the 454. I went out and checked it, and the front drive shaft turns freely with your hand when it is in 2wd. Sounds like you had a problem, you probably fixed it by now!