NP208 Clunking while Cruising in Drive

[RamJetFSJ]

Trying to figure out what a server clunking/tapping sound is coming from my driveline, and have possibly narrowed it down to my very old NP 208 Transfer case. It happens with little load (cruising), and as soon as I downshift (and start engine braking) or upshift, (no load at all)? If I do not shift, it will contine until I slow down significanly. It will also go away if I apply throttle. It sounds like a loose converter bolt sorta, but Ive checked mine, and I dont think my flexplate is cracked, so I doubt that is it. Front inside the car it really sounds like its coming from the back of the drive train, not up by the motor. Seems to be most prevelent in drive, but thats the only time I really cruise at a steady throttle, and seems to go away when shifting into OD. And, it doesn't do it all the time. Sometimes its quite as can be.

I am getting a significant clunk while moving the tailshaft of the TC back and forth, even with the rig on the ground and the transmission in drive. Heres a video

Doesnt sound right to me, but my spare NP208 seems to do it too although not as bad (also, really old). Im running 400 ft lbs though this TC, and I have not regeared yet, and have a lower 1st gear (700R4) so Im applying a lot more torque then it is used to seeing. It did not do it after the fresh motor/trans install, but has progressively gotten worse, and is now really bad (only about 400 miles total). Ive only found 1 other video of someone spinning a NP208 and it didnt make any noise. Does this seem like it could me my problem, and if so, would a rebuild fix it do you think? Or should I look for a fresher TC?

[candymancan]

Chain slack..my 242 and 249s do that too but i dont think thats abnormal what you did in your video.

Now my 249 has bad poping when i change from drive to reverse and when driving under 35mph it vibrates and makes rubbing sounds. Which is is an indicator to me my chain has severe slack and is rubbing the transfercase by dragging. Also bad bearings as the oil turns into a water consistancy quickly which is a sign of excessive heat.

If this is like yours id think you got some bad bearings or a stretched out chain.

But all my transfer cases will wiggle back and forth like that if disconnected from the differential.

[RamJetFSJ]

This is in 2HI, so the chain is not spinning (I dont think). It must be really bad bearings, or the connection between the input and output is sloppy (not really sure how that works in this Tcase, and all the rebuild manuals I had bookmarked are all gone). Wiggle, yes, I understand, but clunk and clank like that?? Obviously I have some slack in the rear end also, but the TC is audible, and loud and getting louder. I sorta want to take apart my spare 208 just to see how it works.

[RamJetFSJ]

The more I think about it... That video is with the rear drive shaft installed, jeep on the ground, in park and ebrake on. Brand new drive shaft, so no slop there. I think there is enough slop in the rear end that it is chattering on the gears while coasting, and making the transfercase clank like that. The rear end is probably making some noise too, but Im not hearing it over the really loud transfercase sounds. Possible?

[Stuka]

The play is not excessive at all from the looks of it. I can't say that I have heard the 208 in my J10 make that sound when going from coast to load, but doesn't mean it doesn't make it. I have had bearings fail in my 208, and it made a hell of a noise, so I don't think thats your issue. Its possible there is more internal wear that makes the noise a bit more apparent. But I personally would not be concerned about that.

[RamJetFSJ]

Thanks Stuka. I definitely have something not right. Gotta keep looking I guess! Just wish I could hang on to the undercarriage while someone else drives to figure out where the noise is coming from. - Its not just one clunk, like I would expect from that kind of play (when going from coasting to load), more like continuous clunk clunk clunk matching road speed. But only in the higher gears while coasting. Might be in the transmission too, who knows.

[Stuka]

Ahh, that changes things. When the rear output bearing started to fail in my truck it starts off as just a kind of ticking sound, almost like a metronome. It started to get worse, and then one day it completely ate itself. That was one of the worst sounds I have heard from a vehicle. When the output was pulled, only tiny pieces of bearings were left.

[RamJetFSJ]

Ill try and get everything back together and get a video of the sound while driving.

[candymancan]

I dunno to me thats alot of back and forth motion if that was your rear drive shaft connected to your diff.

on my 90 i can grab the shaft and nothing moves.. Disconnected the drive shaft and grab the diff yoke and still not a mm of back and forth movement.. even with the wheels off the ground. I have no play at all in my differential.

My other 2 jeeps dont have any play either.. They all got that slack in the transfercase but not the diff

[RamJetFSJ]

Yeah, its seemed excessive to me too. I havent touched the 20 rear end yet, save for brakes, as I want to do it all at once with a gearing change. But its for sure has a bad pinion seal, and im sure the rest of it needs freshening up. I put it all back together, and I do get a minor clunk when going back and forth between reverse and drive, but nothing really alarming. - Im going to throw my pressure gauge on the trans and confirm all my pressures are the same as when I installed it. It could still be a converter problem, or a cracked flexplate, possibly, but I dont think it is. I still think that cruising at 30ish mph in drive is giving just the perfect about of pressures for the rear end to chatter a little from being sloppy, and making the transfercase clack.

[Stuka]

Well, the next test may be pull the shaft, and then check rotational play in both the diff and the t-case. To me, the play in the video doesn't seem bad for a vehicle with a lot of miles. I have seen WAY worse.

[candymancan]

dumb question maybe, but how are your U joints looking ?

[RamJetFSJ]

U joints are fine. Less than 400 miles on a fully rebuilt shaft.

[fulsizjeep]

I am wondering about the rear differential and am curious if you have tried driving it in 4Hi (hubs locked) with rear driveshaft removed to see if the noise is still there.

[RamJetFSJ]

Theres definitely a little more play in the rear end than you see in the video. With the TC in neutral, or the trans in neutral, theres a bit more play, maybe 50%-70% more. Could that much play at certain speeds and loads cause the rear end gears to chatter a bit, sending that on off on off motion up the drive shaft to the Transfer case? I also noticed my rear u-joint angle is a bit more than Id like it to be, maybe 3.5 degrees (normally looking for 1-2 deg). That could be introducing some pulsations possibly? But I can cruise at 85 MPH in OD no problem with not vibrations or noises. It only happens in the 20-35ish mph ranges it seems.

[fulsizjeep]

Just about any of that is possible I guess. I'll switch gears to an experience I had once. In 88 I bought an 84 GW with the NP229 vacuum disco front axle and vacuum shift 2wd-4wd. The next year I had a similar noise driving around 25-30. It drove me crazy. The sound got barely noticeable in 4wd. I finally located the clicking noise in the rear output shaft housing when all 4 wheels were off the ground. When I removed the yoke and housing, one of the output ball bearings was floating loose inside. At least it was pretty isolated from the inner workings of the tcase. A new bearing and it was good to go. It only had about 55K miles on it at the time.

[RamJetFSJ]

Well, after double checking my trans pressures, and doing a little more test driving.. It comes and goes, mostly at a steady state of light throttle, both in Drive and Overdrive - 30-40mph range, and Im pretty confident its coming from the transfercase after driving with my head on the tunnel. And I am getting quite a clunk going from Drive to Reverse and back, especially when the car is on high idle. Im pretty confident its the slow in the rear end causing the chatter, but well never know until I get the cash to have the rear end regeared. I did pull my spare 208 out of the junk yard section, and drained all the water/mayonnaise/ATF - looks like the breather tube is missing, leaving an easy ingress for rain water. So Ill pull that apart one day, and see if its rebuildable. Thanks everyone for their input.

By the way, Ive recently replaced all the shackle bushings, the ball joints and sway bar end link bushings, and the Wag is driving beautifully (besides this clicking), better than ever! Maybe its time for a road trip...

[nutwood]

I wouldn't be complacent about a transfer case clunking as it spins. In 2wd high there's nothing in there that'd do it if everything's good. About twelve years ago, I had a similar noise that I couldn't track down, then suddenly I just couldn't move. Middle of town, right in a narrow (and only!) entrance/exit to a carpark. Went to pull away, no connection from engine to wheels! Turned out it was a fractured input shaft to the transfer case (NP208). It just let go. No warning, apart from the clunking. Also destroyed the gearbox (T400) in the process, not just the working bits but the physical housing as well!
Mind you, it could just as easily be something relatively harmless, but I wouldn't live with it, coz you just don't know!

[RamJetFSJ]

Thanks for the input. I don't put very many miles on this rig right now and am always within AAA tow range. I'm in the middle of doing a basic rebuild my spare 208 right now (seals and 1 bearing). Its it pretty good shape, save for the water that got in it. Luckily not much rust damage or anything on the inside. Once its in, Ill pull apart the old one and see if theres anything weird going on (and see if the sound goes away or not!).