02 Mercury Mountaineer "rear dragging" problem caused by new/old tires...maybe?

[Bigcee]

Hi all,
My father in law has an 02 Mercury Mountaineer and it has had a "grabbing/dragging" problem from the rear tires since she got two new front tires on it. The rears have about 1/8" less tread on them, so that is 1/4" less diameter (tires are same brand/model) than the fronts.

I've already examined the parking brakes on the rears as well as the brakes and rotors. I've also changed the rear diff. fluid w/ synth 75w-140 w/ Ford Motorcraft friction modifier added.

I've also thought it could be ABS, but I disabled ABS to see if that was it and it wasn't....

What do you guys think? I hope it's not a bad rear differential or transfer case....
The fluid didn't look terribly chunky or viscous, and there wasn't any big metal shavings...only the little gooey stuff that came off of the fill plug magnet.

[rasterman]

Swap the wheels on one side of the car? The diffs would act like the car is turning when it isn't, but at least that's a thing that normal cars do: turn. Normal cars don't have different wheel speeds for the front & rear axles.

[1 Lucky Texan]

I dunno anything about those cars, but if you suspect torque bind, swap one rear tire with one front tire. If it has open differentials , torque bind shouldn't be able to develop with different size tires, left-to-right. It's when one axle has a smaller tire that slippage is detected.


edit; DOH, beat by 2 minutes!

[grossgary]

what does grabbing/dragging mean? if it has a 2WD option like Subaru - does that change anything?

Brake hose seems likely. Are there any signs that it may be the brakes dragging? based on your comments about checking brakes it sounds like there is. the hose can collapses internally and allows pressure to brake, but then "holds" the fluid pressure, not allowing it to release or "unbrake". i've never seen it happen on subaru's, but this is a 10+ year old Ford/Merc product, i wouldn't be surprised. you would want to find out which side feels like it's grabbing so you can replace the flexible hose at the wheel. rockauto can have killer prices for these, just make sure it's the right one, easy to get the wrong part from that place.

are the rear struts/springs tired, those will allow a tire to drag...but probably not grab?

[there4igraham]

When the problem is occurring are any dash lights illuminating. Traction control perhaps?

[arthuruscg]

Originally Posted by Bigcee

Hi all,
My father in law has an 02 Mercury Mountaineer and it has had a "grabbing/dragging" problem from the rear tires since she got two new front tires on it. The rears have about 1/8" less tread on them, so that is 1/4" less diameter (tires are same brand/model) than the fronts.

I think the Mountaineer has the full time AWD system and it needs 4 matching tires due to the viscus center coupler. I believe Ford calls for no more then 1/2" CIRCUMFERENCE not diameter.

He needs to bite the bullet and get 2 more tires.

[Subyblue]

OP You might want to check out the ford explorer forum (serious explorations, i think). They cover Explorers and Mountaineers of all generations.

[Bigcee]

Hey all,
Arthuruscg hit the nail on the head! Thanks for all the responses!
He put two new tires on it today and that took care of it.

[arthuruscg]

If he got the same tires, have him keep the good ones for spares. That way if something happens to 1 of the tires, he might get lucky and be able to use one of the old tires.

[grossgary]

he can also use the old tires later and rotate them out if he wanted.