[SoCal LS-L]

Originally Posted by oab_au

The ABS should not have anything to do with it Chris.
The thud is a delay in the action between the TCU signal to the C solenoid and the transfer clutch piston applying pressure to the clutch. It allows the front wheels to start spinning, before the rear is engaged.
It can be caused by the Transfer valve sticking in the valve body, needing more pilot pressure to move it.
An oil pressure leak in the clutch cylinder.
Or the actual clutch plates have worn down too much.

It is this type of delay that breaks the clutch hub off the transfer gear, so I would not let it happen too much.

Harvey.

Im glad I asked. Thanks Harvey, I guess ill keep it FWD until I really need to use it.

Edit: Question, so how does the TCU detect the front wheels are spinning?