Viscous Coupling (AWD) and tire circumference

[soloist3]

I took a brief look around and found that nobody had really mentioned this, if I missed something than this will just be a friendly reminder. Remember, all of us that have AWD equipped Explorer's/Mountaineer's, to always keep your tires inflated equally and tread wear as even as possible, this is of course most important between the front and rear tires. As a difference of 3/16" or more in total circumference between the front and rear will cause your VC to "think" that you need 4x4 when you don't and prematurely engage, repeatedly, shortening the lifespan of your viscous coupling unit.

 

[my pos mounty]

I took a brief look around and found that nobody had really mentioned this, if I missed something than this will just be a friendly reminder. Remember, all of us that have AWD equipped Explorer's/Mountaineer's, to always keep your tires inflated equally and tread wear as even as possible, this is of course most important between the front and rear tires. As a difference of 3/16" or more in total circumference between the front and rear will cause your VC to "think" that you need 4x4 when you don't and prematurely engage, repeatedly, shortening the lifespan of your viscous coupling unit.

Also, since this has recently reared its ugly head on me, keep in mind that even though the tires say they are the same size on the sidewall (and the tire saleman swears they are as well), DO NOT BELIEVE IT!! Measure it yourself. Bought the Michelins, went on road trip and inadvertantly stopped in a rough neighborhood. Came out of the "open all night" diner to two of my one-week old tires stabbed in the sidewall. Of course the ONLY tire shop open on Sunday did not stock Michelins, only had Goodyear Wranglers. I was assured by the recent highschool graduate behind the counter that the Wranglers were indeed the same circumfrance (maybe he didnt know the meaning of the word??). Took his word for it (my stupidity) and drove around on these for 3500 miles. Blew up my front diff (overheated and blew ALL the seals, quite a smell too), wheel bearing (possibly weak beforehand), and an axle. At first just thought my luck was tanking, then, while removing my front differential my mind awoke. I measured the Wranglers against my Michelins... 1 inch difference!!! Damn I feel stupid. The bright side is, I can now take apart a 99 mountaineer front end, fix it and be back on the road in under 2 1/2 hours.

 

[Turdle]

Yes
different brands, and grades, of the same TIRE SIZE may have different rotations per mile, believe it or not.

 

[pricetag2]

Circumference is critical!

I had four well used Contis on my 98 EB AWD. Picked up a piece of metal in a sidewall and had to buy a new tire. A few months later, the viscous clutch goes out and I learned how to change a transfer case. Four new Michelins are on it now to make sure this doesn't happen again!

 

[my98nnj]

I rode on new wranglers up front and totally worn out tiger paws in the rear for almost a year without any issues with the TC. I don't think that small of a dif in tire size is really going to upset things. I think there's more allowance then we think between front and rear DS speed before the VC starts working.

 

[Carguy3J]

I rode on new wranglers up front and totally worn out tiger paws in the rear for almost a year without any issues with the TC. I don't think that small of a dif in tire size is really going to upset things. I think there's more allowance then we think between front and rear DS speed before the VC starts working.

First, why would you put the new tires on the front of a RWD (usually) vehicle?

Second, good luck with your ticking time bomb. Are you sure you actually have AWD, and not the Auto 4X4? Do you have a V8?

 

[Carguy3J]

Also, since this has recently reared its ugly head on me, keep in mind that even though the tires say they are the same size on the sidewall (and the tire saleman swears they are as well), DO NOT BELIEVE IT!! Measure it yourself. Bought the Michelins, went on road trip and inadvertantly stopped in a rough neighborhood. Came out of the "open all night" diner to two of my one-week old tires stabbed in the sidewall. Of course the ONLY tire shop open on Sunday did not stock Michelins, only had Goodyear Wranglers. I was assured by the recent highschool graduate behind the counter that the Wranglers were indeed the same circumfrance (maybe he didnt know the meaning of the word??). Took his word for it (my stupidity) and drove around on these for 3500 miles. Blew up my front diff (overheated and blew ALL the seals, quite a smell too), wheel bearing (possibly weak beforehand), and an axle. At first just thought my luck was tanking, then, while removing my front differential my mind awoke. I measured the Wranglers against my Michelins... 1 inch difference!!! Damn I feel stupid. The bright side is, I can now take apart a 99 mountaineer front end, fix it and be back on the road in under 2 1/2 hours.

I would try to make that tire shop pay for the damage. You relied on their "expert" opinion, and it caused severe damage to your vehicle. I would talk to the manager first, but if that doesn't get you anywhere, take them to small claims court. Obviously, stupid people can't learn with their brain, so they need to learn through their basic instinctive responses. If it "hurts" (in this case financially), then they won't do it again.