We remember the speed of the car and the engine speed, at which vibration occurs in the area of mounting the transfer case.
With the car at a standstill, we move the gear levers and transfer case to the neutral position and start the engine. We set the number of revolutions of the crankshaft corresponding to the speed of the car at which vibrations occurred. If the vibration persists, check the condition and fastening of the power unit supports.
If no vibrations are found, repeat the previous test by engaging direct gear in the gearbox. If this time the vibration manifested itself, the intermediate shaft is faulty (the flanges are loose, the hinge is stuck, the elastic coupling is cracked, etc.).
If there are no vibrations, we accelerate the car a little above the marked speed and move the gearbox and transfer case levers to the neutral position. The causes of vibration in this case are the imbalance of the center differential, the front or rear driveshafts, and the jamming of their hinges.
We also check the fastening of the transfer case to the body: the condition of the rubber-metal supports (tearing and delamination of rubber are unacceptable), tightening nuts, no fatigue cracks on the body.
Before centering the transfer case, we check the condition of the supports of the power unit and the correctness of their installation (the centering washers of the engine mounts must fit into the corresponding holes in the side brackets). We install the transfer case on the car, without tightening the nuts of fastening the brackets of its suspension to the end. By moving the transfer case in the longitudinal, transverse and vertical direction (tightening or loosening the nuts of its fastening), we achieve a minimum and uniform gap between the flanges of the intermediate shaft and the drive shaft of the transfer case (flanges must be at the same level and parallel to each other). We fill the gap between the floor of the body and the supports with shims and combine the centering belts of the flanges by slightly moving the transfer case forward (by the size of the gap between the flanges). Finally tighten the transfer case mounting nuts.