Transfer Case

[mattlou]

Front Diff.

I have a 2004 mountaineer, that I had a blow out recently and had two new tires put on, the same size, but made by GoodYear.

Yesterday the Transfer Box went out and now Ford says its because of the new tires.

Any advice or any truth to this.

screwed this one up.

I meant the front dif. on a AWD mountaineer. There telling me this morning that the circumference is .5 larger on the new tires.

 

[CodePoet]

Sounds more like they dont' want to make you pay for the work. If the tires are the same size it wouldn't have cause the x-case to "go out".

 

[jrford]

What transfer case is it? AWD/ControlTrac? What was the tire size orginal and new?

 

[IZwack]

whats there to worry? isnt that 2004 still under the 'drivetrain warranty'?

 

[mattlou]

they dont want to cover it, because they said that i should have put 4 new tires on.

 

[IZwack]

thats just silly.. anyways, did they tell u exactly whats wrong with the transfer case?

 

[jrford]

Is it the viscous clutch that’s failed? How many miles?
If your 2004 mountaineer = AWD, then you have Viscous Coupling, these are always egaged. I have heard they can go anywhere from 50k to 100k+, depends on how its used. Best way to describe it as a friction plate when the F/R spin axels at the same rate there is no wear. If the F/R axels spin and different speeds all the time then the friction plates will wear down faster. Similar to manual 5sp and a clutch it will only last so long, depend on how much you use it. If the tires are very different front/rear then Yes you could burn the Viscous out, it could happen. Example if you had a full size tire and you put on small donut spare then it would burn out the Viscous Clutch if you drove over 50miles or so and over 50mph.

FYI - On all wheel drive AWD a Viscous Coupling is always on, thus he,. You can't tow a AWD (must use Flatbed). You also have a full size spare for a reason, (similar to a PosiTraction a rear end).

 

[Dr Plastic]

This is probably true. Audi says the same thing for owners of Quattro equipped cars.

When tires wear they get smaller in diameter due to the friction of the road wearing rubber from the tread. if you just replace one or two tires then what you have is tires of different diameters. This causes the viscous clutches to remain engaged because tires of differing diameters will rotate at different speeds. The car interperts this as slippage and engages the clutches. If this goes on for very long times it will cause the clutches to wear out and eventualy fail.

Owners of Audi quattros must replace all four tires, even if only one is bad. If not then premature failure of the differentals is not covered under warrenty. they can go into the computer and see what the tire rotation values are to see if that is the case.

Try taking it to a different, more user friendly dealership.

 

[mattlou]

now if the jack ass at mercury would have explained it like you two just did, I would have understood. thanks for the info.

 

[jrford]

Found a good Link: "Information on 4WD, AWD, and Transfer Cases"

Search on AWD + Tires and you will find this:

"AWD POWER TRANSFER UNIT FAILURE
Normally we associate an All Wheel Drive (AWD) system as one that is inteded for use in inclement weather and will operate smoothly on dry pavement. The system is usually designed to allow for a difference in front-to-rear axle rotations. Chrysler acknowledges an extremely high failure rate of their Power Transfer Units (PTU) used in 96-2001 AWD Town & Country, Caravan and Voyager vehicles. Chrysler said it was a design flaw, but later determined that the failures were due to lack of poper tire rotation. Failure to rotate the tires results in uneven front-to-rear tire wear. The variation in the tire circumference from front to rear results in an extreme heat build-up in the PTU. The condition occurs as a result of the continuous variation in rotational speeds and torque transfer between the front and rear drive components. A tire circumference variation as minimal as 0.5% can overhead the PTU. Chrysler recommends a tire rotation at 7,500 miles or less. Watch the air pressure from front to rear, as it can promote the same. When a tire replacement is necessary, chrysler recommends replacing all four tires with a matched set from the same manufacturer. At a cost of $1,200 for a PTU, a little tire maitenance makes good sense."

 

[gijoecam]

I'm sorry, but 0.5" of circumference on a 30" tall tire works out to roughly 0.2% difference in circumference..... that means that thelarger tire rotates roughly 0.72 degrees less for ever rotation of the smaller tire.... changing the pressure by 5 psi will have the same (or greater) effect on rolling circumference.

I think it's a pile of BS..... so what are you supposed to do if you have a flat tire? NOT put the spare on??? Not a chance..... I'm not buyin' this one.

-Joe

 

[jrford]

so what are you supposed to do if you have a flat tire? NOT put the spare on???
-Joe

You have a full size for a reason. For Short distances I would expect no problems but I would leave it on.
What this may explain is why viscous clutches TC wear out any where from 50k to 100k while non-viscous TC last longer(Jeeps, nv242, nv249). I read about a lot of Jeeps and some have a problem with early wear viscous clutch. With a Jeep you get a full size if you get a QuadrTrac (Viscous) They even had a recall few years back for Jeeps w/Viscous and a small donut spare, replaced with a full size.

It depends on miles, tires and air pressure, size difference of the tires and state of the viscous prior to the replacement of tires. One way would be never to rotate the tires for 30k. Here is an exaggeration for a rough idea. By never rotating the tires at all you wear front tires down to lower than -.5" than the rear, then add new front tires for a +.5 diff thus you actually have over an 1.0" difference for 20-30K miles. Thus for every mile a tire rotates 245-65-17 @ 706 times a mile and times 20k miles and you have over 14,120,000 rotations. This may be just enough. If you rotate and keep the differences <.05" then the viscous may not be used in this case and may last longer, how much?? I don't know, but I'll keep you posted as I usually keep my trucks for 10yrs and well over 100k.

In essence in the majority of cases it shouldn't matter, however a little bit goes a long way to helping or hurting.

For me after this discussion I rotated my tires last weekend and checked all the tire pressure. I will not allow any pressure difference what so ever (< 1lb diff), and now plan rotating the tires every Oil change. My 11yr Jeep XJ 150K (sold), My 9yr Jeep ZJ now at 105k both have had the nv242 TC, both needed rebuilds at about 100k.

Good discussion I have learned a lot about my new X. Thanks all.
Jim.