2nd Gen Non-Engine/Transmission Help-loud clunk/bang in 4WD only

[tstephens]

I have searched this topic several times and nothing seems to specifically target my problem. This just started a few weeks ago when we had some light snow, I put it in 4WD and there was a clunk that sounded like the front driveshaft maybe. So, I took it out and made it home in 2WD. The other day I got into a little mud, and needed 4WD again-now it clunks even louder. I cannot pinpoint where it comes from-sounds like the transfer case area. If I back up or go forward slowly, it is in time rotationally, meaning every 10 feet or so that I go it makes a loud clunk, almost a snap sound like something is binding then releasing.

I have checked the vacuum on the CAD lines and vacuum tested the CAD itself, they check out OK, and the 4WD indicator light works properly-anyone have any ideas?

Oh-my truck is a 99 quad cab if that matters.

Thanks

 

[ttbird]

Sounds like either front driveshaft universal joints or front axle u-joints. Put in four wheel drive and jack up either front wheel. Turn wheel and if it's the axle joints you should hear and feel the bad joint when turning the wheel. You should not have your wheels straight but turned either way. Also check driveshaft for play. If it's that noisy is should be pretty easy to find. Don't know your mileage but I'm going with axle joints.

 

[fox]

If you are rolling straight ahead, then my guess is the diffs are geared different.

What is the history of this truck?

 

[tstephens]

Thanks for the suggestions guys-

I will jack up the truck to check the front u joints, but the sound feels like it is coming more from the center of the truck. I don't think I have a driveshaft problem because the shaft spins feely by hand when in 2WD, although I will try prying on the CV joint.

My gear ratio is 4. 10 front and rear-have had this truck since 2000, and it has 105,000 miles on it now-any other ideas? thanks again

 

[DieselDoghouse]

OR you may have a delay in the engagement of the slide coupling for the CAD. Your front shaft is powered up and the vacuum is trying to advance the collar (inward I believe) but it the collar is encountering the moving splines on the other shaft (a slight revolution difference) and can't lock. You can pull the CAD by removing the 4 flange bolts (careful - they may be siezed: replace with stainless metric) and clean the shafts and coupling collar. Also when you engage 4WD feather the throttle back/forth to "shake" the shafts torque-wise for better shaft lockup.

 

[NHonch]

I had the same problem,it would clunk,but not catch all the way on the splines of the front diff where the vacuumed valve is located
The valve apparently just got tired and replaced it and no problems
Maybe check your little driveline that goes to your front diff to your transfer case,there are two universals there that articulate and they could have moisture or dirt there,depends on how long you have used your 4x4 before your clunk problem

 

[tstephens]

Thanks for the suggestion, but I am pretty sure its the transfer case. It does go into

4WD OK, and it works, but it really bangs every few revolutions of the tires. I am only using it in emergencies until spring when I can get under it in decent weather to replace or rebuild the TC (truck wont fit into my tiny garage). If I go very slowly in 4WD and hold to door open, the sound clearly comes from the center of the truck.