Could someone please explain how tire size destroyed my transfer case?

97 Explorer.
Diagnosed as needing a new transfer case.
Guy took a caliper and measured the diameter of each tire and found
the right front to be about 1/2" smaller than others and declared that
to be the problem that caused the failure. It was worn and needed
replacement.

How did the diameter of one tire cause this problem?

One of the reasons I"m confused is because there have been many times
during the life of this car when the mechanic has warned me that a
tire or two has too much wear and the 'case hasn't failed.
Is the the results of differing tire sizes (due to wear) over a 9 year
period?

He wants to replace all 4 tires, although the other three appear to me
to be in good shape - Mike

Mike,

I had a similar problem in 1998 with my 98 Eddie Bauer. The spare
was of a smaller circumference than the other three tires. After about
50 miles of driving, smoke was pouring from the transfer case as was a
good deal of fluid. After a tow to the Ford dealer and a 30 day
repair, I got my Explorer back. Since then, I've been much more fussy
about the age and sizes of the tires. The problem has never returned.
It doesn't take but a little math to realize that when the
circumference of the tires on the same axle differs by even a little
that the cumulative effect that the transfer case sees over distance
traveled adds up fast and may lead to trouble.
By the way, last month I replaced my Michelin LTX M/S with 84000
miles on them with a whole new set of Michelin LTX M/S.
SWEET!

Best of luck to you!

Michael Horowitz wrote:
> 97 Explorer.
> Diagnosed as needing a new transfer case.
> Guy took a caliper and measured the diameter of each tire and found
> the right front to be about 1/2" smaller than others and declared that
> to be the problem that caused the failure. It was worn and needed
> replacement.
>
> How did the diameter of one tire cause this problem?
>

I recently posted this info on how your transfer case works in the
thread about the 1995 Explorer update. Note that you can't select true
2 wheel drive. If the computer thinks a wheel is slipping, it engages
the transfer case. There is a "brown wire mod" that allows you to stop
the transfer case from engaging in this case. Here's the info:


97-'01 (switch says, 4auto, 4high, 4low)

The '97-'01 model years lack a true 2 wheel drive option. With a live
front axle, there are no significant mileage gains to be had by driving
the rear wheels alone. That being said, some of us simply prefer to
determine when the front wheels should drive and when they shouldn't,
instead of relying on a computer to make that decision for us.

In 4 auto, the GEM monitors the wheel speeds. When it determines that
there is wheel slippage, it sends the signal to the Torque On Demand
relay to actuate the Transfer Case Clutch Coil via the brown wire.
******************

So the computer interpreted the smaller wheel as slippage and engaged
your transfer case on pavement. The "brown wire mod" would allow you
to defeat that.
-Paul

Couldn't find your reference to the mod, please provide more info on where
it is posted

Bill

> wrote in message
oups.com...
>
> Michael Horowitz wrote:
>> 97 Explorer.
>> Diagnosed as needing a new transfer case.
>> Guy took a caliper and measured the diameter of each tire and found
>> the right front to be about 1/2" smaller than others and declared that
>> to be the problem that caused the failure. It was worn and needed
>> replacement.
>>
>> How did the diameter of one tire cause this problem?
>>
>
> I recently posted this info on how your transfer case works in the
> thread about the 1995 Explorer update. Note that you can't select true
> 2 wheel drive. If the computer thinks a wheel is slipping, it engages
> the transfer case. There is a "brown wire mod" that allows you to stop
> the transfer case from engaging in this case. Here's the info:
>
>
> 97-'01 (switch says, 4auto, 4high, 4low)
>
> The '97-'01 model years lack a true 2 wheel drive option. With a live
> front axle, there are no significant mileage gains to be had by driving
> the rear wheels alone. That being said, some of us simply prefer to
> determine when the front wheels should drive and when they shouldn't,
> instead of relying on a computer to make that decision for us.
>
> In 4 auto, the GEM monitors the wheel speeds. When it determines that
> there is wheel slippage, it sends the signal to the Torque On Demand
> relay to actuate the Transfer Case Clutch Coil via the brown wire.
> ******************
>
> So the computer interpreted the smaller wheel as slippage and engaged
> your transfer case on pavement. The "brown wire mod" would allow you
> to defeat that.
> -Paul
>

>>How did the diameter of one tire cause this problem?


Read the article:
http://www.tirerack.com/tires/tirete....jsp?techid=18

That should help answer your question.
















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Posted via a free Usenet account from http://www.teranews.com

Bill wrote:
> Couldn't find your reference to the mod, please provide more info on where
> it is posted

Here's info on the "brown wire mod" with pictures for the 1995-1996
Explorers:
http://tinyurl.com/y5hzu9

Here's the "comprehensive brown wire mod" info, covering '95-'96 and
'97-'01 model years:
http://tinyurl.com/ycyp54

Note: not for AWD vehicles.

Why do this mod:

Some of us simply prefer to determine when the front wheels should
drive and when they shouldn't, instead of relying on a computer to make
that decision for us.

Background on the "brown wire mod":
There were three slightly different systems included in the
second-generation Explorers. The All Wheel Drive is a full-time system
and cannot be modified to be full-time four-wheel drive or two-wheel
drive. The second and third systems used in the '95-'96 and '97-'01
model years were both called 'Control Trac 4 Wheel Drive' Both systems
used the (insert model here) transfer case. The '95-'96 used a front
axle equipped with a Center-Axle Disconnect, which was done away with
on the '97 model year in favor of a live axle (and fewer parts to fail
when needed most)

Depending on the operator selection, the transfer cases in both systems
were actuated by one of two GEM-controlled sources: The Torque On
Demand Relay and the Transfer Case Shift Relay. The transfer case
contains a Transfer Case Clutch Coil, which is what locks the front and
rear driveshafts together. Power for the TCCC is fed via a brown wire,
hence the familiar name.