Odd running gear noise

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OregtoJohn

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Newbie to forum here. I just acquired an '01 which is full-time AWD [also has 4WD Hi or Lo selectable]. About 150K miles, old receipt shows tranny rebuilt at 125K. Drives well, except now and then just moving along at 35-45 mph steady a sort of noticeable rap in the drive train, but no effect on driving. This means no jerkiness or odd motion. The book says this AWD works by switching between 4- and 2-wheel drive "as required," and I wonder if the noise is this shift, maybe coming from the transfer case? A normal sign of wear [I hope!]?
 
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OregtoJohn

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Yes, a distinct knock. No extra vibration accompanies this. And it's just one knock. Just happens sometimes.
 

Robert Wagner

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With the transmission engaging overdrive, I would expect a RPM change. My 2000 XLT has a enable/disable OD switch.

Another thought would be the torque converter being switched to locked mode and that may not necessarily change the RPM.
 
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OregtoJohn

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Locked converter? Interesting idea - I could find no suggestion of when this would occur, in my manual, but it's not very elaborate. Yesterday I did follow said manual's suggestion and change the transfer case's fluid. This should be done regularly, unlike the differentials. The fluid, same as transmission oil, came out cloudy and dark; not bright red and chipper like new fluid. I think this was overdue. Unknown whether this will affect the issue above, but will see in a few days.
 

Trainmaster

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Rear transmission mount is known to clunk when worn. Check motor mounts, rear and front suspension and universal joints.
 
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OregtoJohn

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Excellent suggestion on that tranny mount - easy enough to have a look tomorrow!
 

Yupster Dog

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The fluid, same as transmission oil, came out cloudy and dark; not bright red and chipper like new fluid. I think this was overdue. Unknown whether this will affect the issue above, but will see in a few days.
You are on the right track. The shudder at 45 is common thing. After I had the transmission filter, fluid and transfer case fluid change i still had the shudder for about 100 miles or so then it fades away.
I had mine done at the dealer, that's what they told me and sure enough it went away and no problem since.
 

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