'02 3.9L dak, replaced the TCCM, was super stoked to have indicator lights for the first time. First test of the 4wd, and I heard a cla-clink cla-clink coming from the front of the vehicle. Asked my friend with some mechanical experience to take a ride and he immediately said it was the CV shafts. Ok. Found both sides with hubs for cheap, and ended up having to replace intermediate shafts as well. imagine my utter disappointment when after $250 worth of parts, I test the 4wd and the same noise begins grating on my ears... Still. While changing the shafts I noticed a leak Fromm the front diff cover gasket, and had to put a significant amount of gear oil in it. So, the question: what do I look at as the next possible culprit?

 

This might be a clue. Unfortunately, putting in more oil does not make the damage/wear already done go away.

 

yup, front gears sound torched.

That said, aren't our trucks constant drive on the front? I would think the noise would be there all the time. Maybe different ratios or torn up transfercase teeth?

 

Pull the cover on the front differential. Everything rotates any time the truck is moving. The only difference is that in 4wd it is under power.

 

only difference I can fathom would be torn transfercase gears/chains - in 2WD, the front shaft is "floating". It's still meshing with a gear, but that gear is not engaged to the rear output shaft.

If the pinion and/or ring is missing a tooth, i would find it hard to believe that it would be quiet when running on the 'coast' side of the gear, and made noise on the 'thrust' side. Granted, still possible.

 

I had a similar noise from my 03 3.9 recently. Was more of a rotation clunk. I had already replace CV axles and hubs. It turned out being the u joint on the front 4wd driveshaft. It only made noise in 4wd even though it spins regardless of 2wd or 4wd. The CV side of the 4wd driveshaft made clunking too before I replace it a couple years ago. It's 6 small bolts on the transfer case where the CV portion is and 4 larger bolts on the differential side where the ujoint is. My ujoint had no slop but when I removed it, one cap was so seized up I couldnt loosen it off the end of the joint with a vise and hammer. Oh well, put the new ujoint in and reinstalled the shaft. Problem solved. Overall, it took a couple hours of putting around to remove, replace and reinstall. I also checked the new CV joint for grease and wear while it was out. If you take the shaft out just mark both sides first so you can reinstall in the same position.

 

Sounds like something internal in the transfer case if the noise is only when 4x4 is engaged. One way to test would be to disconnect the transfer case to the forward driveshaft and then spin the yoke by hand with 4x4 engaged (and rear wheels off the ground). then you can get a better feel for any type of binding/grinding as it rotates. Could also start the truck and see if you hear the noise as well with the front disconnected. that should help pinpoint diff or transfer case.