77' Very Weird Clunking While Driving (always slowly) (1 Viewer)

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This is hard to explain, so here is a video:

Today is the first drive of this FJ40 since I've owned it and after a couple laps around the neighborhood with no problems, I pulled out onto the highway. As soon as I got up to maybe 10-15 mph it started this clunking sound, which sounds like it's coming from the transfer case. Naturally I begin to slow down and the clunking slows with my speed but also gets louder and harder. Once I come to a full stop, I can start driving again and the clunking won't return until I get back up to 10-15 mph. The t-case linkage was completely frozen up so it it was stuck in 2H, which is odd but I can't see how it would related.

Both axles have been rebuilt and the noise is definitely not coming from that far down. There is only a rear driveshaft installed right now, and it's new (Tom Woods).
I've disassembled the t-case as much as I can without removing it (inspection covers, front/rear outputs, removed the output shaft/gear) and the output bearings look fine. There is some light hazing on the bearing races and the rollers also look fine. The bearing cages are loose and can be wobbled around, but I'm not sure if that's normal (I can make a video showing all of this if it would help).

Has anyone come across this before?
 
I would put it up on 4 jack stands and test the system by looking/feeling around for the issue while someone else "drives". Maybe its not stuck fully in 2H. There isn't a lot of linkage - free it up.
 
I would put it up on 4 jack stands and test the system by looking/feeling around for the issue while someone else "drives". Maybe its not stuck fully in 2H. There isn't a lot of linkage - free it up.
Good idea, I should have tired that before tearing into it.
 
It's a new driveshaft, so new u-joints and the flange bolts are all tight and it's in phase?
Yes and yes. It's a double cardan.
 
Years ago, as a ‘prank’, we put a longe tie wrap on a guys drive shaft and as it spun, it made a noise very similar to that….as the end of it slapped the bodywork….are you sure there’s nothing on the drive shaft coming loose or maybe the e-brake cable, speedo cable rubbing on something?
 
I've seen the park brake backing plate break the bolts, then break the cable and then that was spinning around.
generally this happens when the park brake is working well and driven while engaged

should be able to diagnose that pretty easily by looking underneath, or jacking up and rotating a tire.
 
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Thanks everyone for the suggestions! Answers below:
What's the state of your PTO?

How many clicks have you got on your handbrake? (Did you take the drum off?)

How does the oil look in the transfer case?
There is noo pto or hand brake on this one (some previous owner). The Tcase was out of oil when I bought it but I filled it and the transmission before driving it.
Years ago, as a ‘prank’, we put a longe tie wrap on a guys drive shaft and as it spun, it made a noise very similar to that….as the end of it slapped the bodywork….are you sure there’s nothing on the drive shaft coming loose or maybe the e-brake cable, speedo cable rubbing on something?
That's hilarious, but sadly not my case here. This machine has lived on my lift for over a year while I've been doing a spring over and rebuilding the axles.
The e-brake cable and speedometer cable aren't connected as the previous owner cut them off a few inches from the transmission.
I've seen the park brake backing plate break the bolts, then break the cable and then that was spinning around.
generally this happens when the park brake is working well and driven while engaged

should be able to diagnose that pretty easily by looking underneath, or jacking up and rotating a tire.
Everything seems fine here too.

I got it back on the lift yesterday and the Tcase disassembled, and everything appears to be fine. I did notice the bearing cages are loose around the inner race but I think that's normal. There are no flats spots on the rollers or races, and only some light hazing on the rear output bearing as shown in the clip below. All other bearings look fine too. I'm starting to think this isn't my problem.

I also ran the engine and went through all of the gears while on the lift and I'm not hearing anything unusual from the transmission, so now I'm even more stumped.
 
Focus on your t case linkage. I had this happen years ago due to accumulation of dirt grime etc and it could drift between 2H and low and would sound horrible.
 
Focus on your t case linkage. I had this happen years ago due to accumulation of dirt grime etc and it could drift between 2H and low and would sound horrible.
It was frozen in place and now with the Tcase apart I'm cleaning and getting everything freed up. I hope that's all it is.
New drive shaft, I would check the flange bolts. I have had mine come loose after reinstalling the drive line. Simple enough to check and a few minutes to tighten down if needed.
I had suspected that as well but it was still buttoned down tight when I pulled the Tcase.
 
With the tires on the ground, transmission in neutral, how far can you rotate the driveshaft/ rear diff flange back and forth? Can you push it up and down?
 
Well I got the Tcase back together without any drama and the problem is gone.... so I'm both relieved and annoyed. I'm going to blame it on the shift linkage and call it a day.
Thanks everyone!
 

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