shake rattle´n mystery

[KLINGSTON]

Hi my astro 95 awd has a periodic problem, it suddenly is shaking heavily, shifting into neutral dosent help, applaying brake dosent help, stopping for a few minutes and start again ussaly helps. Mostly it is at 70 to 80 mph, but also at lower speed. I never knows when it comes, sometimes weeks between. Any suggestions?????

[Blue Bowtie]

Welcome Aboard!

Presuming your van has the New Venture Gear (GM/Chrysler joint venture) transfer case, there may be a problem with the original oil fill. GM issued a TSB in about 2002 for a "shudder" problem with these units whereby the overrunning clutch would rapidly and alternately engage and disengage on acceleration or while coasting. Given the slightly different drive ratios of the outputs, the front driveshaf tshould "freewheel" 99.999% of the time. when the clutch would "shudder" this didn't occur.

The suggested repair is to drain the transfer case and refill with 2L of the NEW factory oil, Auto-Trak II (formerly just "Auto-Trak"). The new oil is a PAO synthetic instead of a mineral oil. The GM part number is 12378508, and is available in 1L (not 1 quart) containers from almost any GM dealership parts department. The proper fill on my 2000 was 1.8L, but I managed to squeeze the two full liters in with no problems, minus what was left in the piece of hose I had to use to fill the unit.