Fighting vibration, front drive shaft spinning in 2 wd

Marksexpy · Oct 31, 2014

1997 with 2wd a4wd 4high 4low

Had a bad vibration starting at 40mph. Diagnosed this to a square weight that fell off the front drive shaft. Got a different shaft from the junk yard and now have a vibration that starts at 60-70 mph.

My issue is that front drive shaft spins in 2wd.
Front axle is disengaging properly, jacked up the back end and the front shaft turns when in drive with the rear wheels spinning. I then replaced the transfer case motor, no change still spins.

When in park i can spin the front drive shaft it has a little resistance. I then tied up the front drive shaft with a ratchet strap, placed in drive and let the rear wheels spin, the front drive shaft did not spin.

Any ideas what is causing this? Can it be fixed without replacing the complete transfer case.

I am thing of driving around in 2wd with it tied up to see if it will loosen up.

stamp11127 · Oct 31, 2014

From the service manual:
In A4WD, the generic electronic module (GEM) varies the torque split between front and rear drivelines by controlling the transfer case clutch. The transfer case clutch allows for slight speed differences between the front and rear driveshafts which normally occurs when negotiating a corner on dry pavement. When the rear wheels are overpowered, the GEM detects this slip condition, and the duty cycle to the transfer case clutch is increased until the speed difference between driveshafts is reduced.

Soooo, if the front drive shaft is spinning about the same as the rear, I would suspect the transfer case clutch may not be disengaging. Might be a GEM issue.

Marksexpy · Oct 31, 2014

Stamp,
Thanks for the reply, I thought the same thing and disconnected the brown wire, nothing changed. I know I am in 2wd but thought i would give this a shot. I have a friend with a 99 150 and his front shaft doesnt turn in 2wd. His front shaft does move a little easier in park when both the front axle and the transfer case is disengaged.

Marksexpy · Oct 31, 2014

Where do i find the gem? In the vehicle. Thanks

stamp11127 · Oct 31, 2014

Usually behind the fuse block.

Marksexpy · Nov 1, 2014

Stamp, thanks again, if the brown wire is disconnected and i am in the 2wd selection the gem should be out of the question of root causes? Am I thinking correctly? I do beleive the clutches are not releasing 100 percent as you stated. This expy has over 300k on it and is still a good truck, so a different transfer case is not out of the question. I would rather figure this one out though because other than this issue the transfer case works great. I just cant stand the slight vinration of the shaft turning at high speeds.

Marksexpy · Nov 1, 2014

Ok so i tied up the front drive shaft with a ratchet strap, drove in 2wd roughly 15 miles getting up to speeds of 80 mph. No vibration.......

Returned home and removed the strap. Drive shaft turns easier by hand in 2wd in park. Then i drove without it strapped in 2wd no vibration. I then tested 4x4 hi and low, worked great.

The clutches must have been sticking and by holding the drive shaft when driving must have broke it free or wore some of the pads away for clearance

Any ways the vibration is gone, we will see how it goes.

Marksexpy · Nov 9, 2014

500 miles and no vibration

Fighting vibration, front drive shaft spinning in 2 wd

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