Tire size and tranfer case going out?


I have a 99 ford expedition I recently had tranfer case go out . ANd was told it was due to front tires different brand than rear - tire size is the same but the brand is different> PLEASE HELP


Different brand and even model tires in the same tire size are slightly different diameter. This diameter difference in AWD vehicles causes constant slippage in the transfer cases due to differing rotational speeds front to back burning them the transfer cases out.

If your vehicle is 4wd and on dry pavement in 4wd there is no slippage except in the tires which put undue stress on the 4wd driveline.


Does this vehicle have push-buttons to put it in 4-Hi and 4-Lo? If this is a manual engage 4wd system, then I don’t think it should be an issue, since the transfer case should only be engaged on slippery surfaces where the difference in your tire diameters shouldn’t matter.

If not, I believe this truck has an automatic 4wd setup, where a computer senses slippage and automatically puts the truck into 4wd when needed. I’m not sure, but it is possible that the computer sensed the different wheel speeds due to differing tire sizes and might have put the truck into 4wd on dry pavement, which will kill a transfer case on a 4wd vehicle very quickly.

It could also be a full-time AWD vehicle, in which case the different tire sizes absolutely led to your transfer case failing.


I’m sorry, but the only help we can offer:

  1. Help you understand that even though the tires say they are the same size, they may be slightly different in diameter.

  2. Help you understand the importance of tire rotation so you don’t put yourself in the position on replacing tires 2 at a time.

  3. Be sympathetic.