Bad Drivetrain Noise

[rowland]

I seem to have some sort of problem with my drivetrain and haven't been able to track it down.



Sunday I was driving from Palmer to Fairbanks Alaska and was about halfway (thats in the middle of nowhere for those that haven't made the trip) When I started to get an intermittent loud clunk/grinding noise from under the truck accompanied by a slight drag on the drivetrain. I pulled over and checked out everything as close as possible. All U-joints appeared to be ok and there wasn't any leaks or anything. Locking and unlocking the hubs didnt' make any difference either.



However I discovered that if I left the hubs unlocked and put the T-case in 4H then the noise went away. I drove the last 200 mi that way in temps ranging from -25 to -50 F. When I arrived in Fairbanks I discovered that even with the hubs locked I no longer had 4 wheel drive. This was a little bit of a problem since my front axle creates so much drag at -45 that I got stuck in the parking lot... twice.



Ok, now for the weird part. This morning it was a balmy zero degrees so I went out to try to diagnose the problem. Funny thing, there wasn't any. Two and four wheel drive work perfectly. T-case shifts smoothly and hubs look fine.



So has anyone had this sort of problem before? I plan on draining the t-case oil as soon a possible to check for metal shavings. Anything else I should check? An NP205 rebuild is around $1000 so I really want to explore all my options first.



Any wise words would be appreciated.



Isaac

 

[cerberusiam]

I thought I was the only one crazy enough to drive thru the middle of no where in those temps. Nice to see I am not alone. Thats about the same experience I have had with any of the trucks using a heavy oil in the transfer case. Anything under -20 and you would think pieces are falling off at random. Howl, growl, vibrate, etc. Its probably just the lube having the consistency of molasses and causing gears to turn and let loose. You can cut 80-90 gear lube into chunks that will hold a form at that temp. Well, pretty close anyway. You might want to look at a synthetic that will operate in those temps and still protect. Drain it and make sure nothing bad is showing would be good protection. When you get used to -40 and the temps get to 0 it is rather balmy. I can imagine what the diffs and t-case think of that. Good luck.

 

[BushWakr - RIP]

Hmmmmm... there must be three of us who do dumb stuff like that then... .



Bob.

 

[rowland]

I usually run Chevron Arctic Grade all around but I honestly can't remember what is in there now. Could be 90W. It was a very nasty noise though, I really was not happy about it. Sort of a CLUNK... grrriiiiinnnddd. The clunk felt like I hit something. I wish I knew more about the how this thing works. Maybe the shifter fork was getting stuck or something. That might explain why I didn't have four wheel drive even though the lever was in 4 Hi.



Yeah, I'm not sure how cold it was in some places... but for about 20 mi the truck didn't want to go over 45 mph. Just incredibly stiff. Even with the radiator blocked off the engine was running cold and there was frost on the doors with the heater turned all the way up. Gotta love life in the north.



Isaac

 

[cerberusiam]

If your shifter is out of adjustment or the bushings are worn its possible it could have been trying to engage the front drive shaft from the oil being stiff. Its possible locking/unlocking the hubs had no effect cuz the grease was too stiff and they wouldn't engage. The sound could be either the hubs or the front drive shaft engagement in the t-case. Since it all started to work right and the noise went away after the temps warmed up its probably just the cold having an adverse effect. Might not hurt to check your hub engagment pieces also to see if there are any suspicious fragments or obvious damage. Good luck.

 

[rowland]

According to my '89 Dodge manual the NP205 takes SAE 30 wt motor oil, API service "SF" or "SF/CC". Of course my friendly local Napa doesn't have anything with that service rating. Does anyone know the consequences of using a quality 10-30W Synthetic?



I did pull the hubs first thing and they appeared to be fine.



Isaac

 

[RGT]

I have had a clunk grind occur when I was using low range on the transfer case without the hubs locked(backing up a trailer) I could never get it to occur with the hubs locked so have assumed that the transfer case was not able to engage fully without the front drive shaft turning.....