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Old 11-14-2005, 13:01   #1 (permalink)
Bill Jeffrey
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BAM! noise from 2002 XLT 4WD

2002 Explorer XLT 4.6L V-8 4WD automatic, factory tow pkg, purchased
Oct/Nov 2001. This is the one with the Control Track 4WD.

During the first 80K miles, I very occasionally heard a single loud BAM!
come from somewhere up front. Maybe 5 or 6 times total. In each case,
the transfer case was set for 4WD Auto, the rear wheels were losing
traction on a slippery/sandy surface, and the front wheels were
beginning to pick up the load. This has been mentioned on this forum,
though not with any light at the end of the discussion.

Now, as I approach 100K miles, it is doing it much more often - like
every 3 or 4 days. But now, the noise occurs on hard dry pavement,
usually (but not always) during or immediately after a turn. Most
times, the noise seems to come from the left front wheel area, but once
it came distinctly from the right.

So what is going on? Am I headed for disaster? And yes, after each
occurrence, I have confirmed that the transfer case was set for
4WD-Auto, not 4WD-Hi or 4WD-Lo.

Thanks for any thoughts.

Bill

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Old 11-15-2005, 01:01   #2 (permalink)
ross via CarKB.com
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Re: BAM! noise from 2002 XLT 4WD

Sounds like your control trac is having issues. There are sensors on the
front and rear driveshafts which tell the computer how fast they are spinning.
If the rear driveshaft speed goes faster than the front, then the GEM will
tell the transfer case to engage the front axle more - it can vary from 10%
or so up to 100%.

If your front axle is over engaging, then that will cause windup tension in
the front axle. That tension can be "slipped" off by the front tires
slipping a little, or it can be released with a thump or bang - usually the
transfer case clutches slipping all of a sudden.

If its the control trac, you will not get this bang on a dirt road as the
tires can slip off the tension.

The most common issue is old dirty sensors - you can pull them out and clean
them, and check them to see if they are still good.

Hope that helps!

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Old 12-08-2005, 16:01   #3 (permalink)
Bill Jeffrey
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Re: BAM! from 2002 XLT 4WD - Final answer

I have posted about the occasional but increasingly-frequent sharp
metallic BAM noise coming from the front end. Tight turns, dry surface,
low speed. Always sounded like it was near the left front wheel. I
self-diagnosed it (always dangerous) as 4WD engaging when it shouldn't,
and winding up the front drive train. Turns out I was wrong.

The answer turned out to be easy but scary. My mechanic discovered that
the bolts that hold the left front axle in place had backed out. The
BAM was caused by the axle moving out of the proper position in the
"cradle", and then slamming back into place. Bolts tightened, problem
solved.

He tells me he has not seen this before, but will start checking all
incoming Explorers. If he sees it again, he will file with NHTSA.

Bill
--------------------------------

ross via CarKB.com wrote:

> Sounds like your control trac is having issues. There are sensors on the
> front and rear driveshafts which tell the computer how fast they are spinning.
> If the rear driveshaft speed goes faster than the front, then the GEM will
> tell the transfer case to engage the front axle more - it can vary from 10%
> or so up to 100%.
>
> If your front axle is over engaging, then that will cause windup tension in
> the front axle. That tension can be "slipped" off by the front tires
> slipping a little, or it can be released with a thump or bang - usually the
> transfer case clutches slipping all of a sudden.
>
> If its the control trac, you will not get this bang on a dirt road as the
> tires can slip off the tension.
>
> The most common issue is old dirty sensors - you can pull them out and clean
> them, and check them to see if they are still good.
>
> Hope that helps!
>

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