'chunk' sound 99 A4WD V6 SOHC automatic w/100k miles...

A few weeks ago (OK, several) my ABS light came on (stayed on after startup); I haven't done anything about it yet except be careful not to tailgate & find out that the rear differential sensor is a known culprit.

I drive 50 highway miles each way to work, & go on off-peak hours, so is pretty steady speed most of the way.

A week or so ago I noticed it making an occasional 'chunk' ... 'chunk' ... sound after warmup, while at steady speed (40 on road, 65 or 70 on highway); a small shudder accompanies the sound, but it is hard to tell where it is coming from. It is not loud, but noticeable.

Sometimes it does it a few times in succession ('chunk' ... 'chunk' ... wait 15 seconds & repeat), then it may not do it for 10 miles or so. A few times it only did it once or twice during the commute.

Doesn't seem to do it at all during acceleration, going up thru the gears, or braking. Overdrive on or off seems to make no difference.

I knew my brakes were pretty well shot, so I had a local shop do them, & change the "100,000 mile" plugs, thinking that maybe it was just a miss or that the brakes may somehow be the cause. No difference, & they are not tranny/transfer case type guys but gave me the name of the local guru.

Before I took it to him, I thought that possibly (not knowing what it looked like) parts from the ABS sensor could have sagged & it was contacting a gear in the differential.

I took the sensor out (new one is on order) & noted that it is a sort of solid cylindrical piece that doesn't have any dangling bits that could come off. I couldn't really tell if the end of it was scuffed enough to indicate contact with a moving gear. What I did see is that there were many shavings stuck to the sensor. I wiped it off & stuck it back in there.

(are shavings normal? maybe I should change the gear oil ...)

The light is still on & the noise remains, same as before. The noise / frequency does not seem to be getting worse, & I will take it to the guru when I have some time ...

Also the "4WD LO" seems to engage, but I cannot tell a difference when "4WD Hi" is switched on. Leads me to believe the mechanism is worn / motor is misaligned? Maybe something is stuck a few degrees off, causing gears to bang together occasionally?

So ... transmission, transfer case innards, 4WD motor action, differential ... ???

I know it is hard to diagnose over the net, but if someone has had similar experience, please reply ...

I WILL be taking it to the local guru, soon ... I promise.

Thanks & sorry for the long post, but thought it necessary to explain the situation. - Rick.

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Rick Young
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