40series

i have bald tires and the tire shops tell me they wont put one new tire one my truck bercause it will mess up my t case.... but will 1 or 2 new tires mess the T case up if i drive it in 2 wheel

FFDP

iTrader: (2)

The tire tread depth needs to be within 3/32nd of each other on the same axle to prevent extra wear on the driveline diffs or transfer case.

Having 1 brand new tire on the left rear and bald tire on the right rear means one tire will be spinning faster/slower than the other and cause wear internally. Same with the front, if you selected 4X4 and had 1 brand new tire on the left front but a bald tire on the right front, the front diff will not be happy and will wear out faster.

In AWD or 4x4 trucks/cars/suv's you should always replace all 4 tires at once (AWD is a must). In a pinch you could do 2 new tires on a selectable 4x4 truck but both new tires must be on the same axle and it's not wise to run the 4x4 with different tread depthed tires on all 4 corners.

Suburbazine

If you have a locking rear differential (G80) you MUST change both rear tires at the same time. The issue that arises with not changing the front tires to match is that the auto tcase has a viscous coupler...this will burn up and die in short order if you were to ever engage 4x4 on pavement accidentally.

Wolftrk99

iTrader: (5)

Or if you are driving constantly in auto 4, it will tear up your carrier bearings in your front diff

Suburbazine

The coupler usually dies first though. When that happens it stops sending power to the front altogether.