Different size tires on front and rear in my 4×4 truck? What will break!?

Recently my old man threw a smaller set of tires on the front of my truck… it snowed and I had it in 4wd… things are no longer right with the tranny or something on the truck… I strongly believe it is because when it was in 4wd the tires do not rotate at the same speed which they definitely need to or something will break or has?? It seems something is on the way out and 4th gear doesn't work anymore…. my question is what will I be needing to most likely repair now? Lessons learned, it was a big oversight on my part. it is a 1991 Toyota pickup -5 speed manual… Thanks for any help!
In Theory what all can break? What is most likely broken already, if anything…. How long can I drive it as is if I no longer use 4wd?

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4 Responses to Different size tires on front and rear in my 4×4 truck? What will break!?

  1. JetDoc May 28, 2009 at 12:46 am #

    When running in 2-wheel drive, the tires on the front and rear axles are free to roll at different speeds when you steer your truck around corners and obstacles in your path. As the two axles are free to run at different speeds, there is no problem with running different size tires, but when you go into 4WD mode, you lock the center differential, which forces both the front and rear axles to run at the same speed.

    Different size tires would still be trying to turn at different speeds, so you would have problems with binding and putting excessive strain on the differential gears. Hopefully, this did not cause any permanent damage, but you do need to get all four tires back to the same size, or leave it in 2-WD.

  2. My <3 belongs to Jethro May 28, 2009 at 12:46 am #

    I believe I heard that screws up your axles….you have to be careful because they can completely snap

  3. schurz04 May 28, 2009 at 12:46 am #

    There is no way to tell without an inspection. You're on the right track with the cause. Realistically, if you have it in two wheel and its doing it, the its the main tranmission. If it only does it in four wheel, then its in the front transaxle and transfer case.

  4. nick September 18, 2010 at 2:59 pm #

    help .help.I have a 97 jeep grand cherokee.I think there very nice.but man is thise one giving me broblems,i just tried the 4×4 and i have diffrent tire sizes.the front are 215/70/r15 and the back are 225/75/r15.the thing is that now my jeep wont desengage the 4×4.i have tried everything.please tell me if i correct the tire size the broblem well be fixed.cause i drove it a couple of miles.thanks for your advise.