A clunk in the driveline has developed recently. I don't notice it when taking off or shifting gears. I only notice it when I am slightly coasting at < 20mph speeds.

For example, coasting in 3rd gear at 20mph on a slight downhill neighborhood road I'll feel the driveline clunk as it goes between coast/drive.

U-joints and slip yoke appear tight from what I can tell. I relubed the rear slip yoke and it didn't seem to change anything. The only question mark for me is that the rear pinion flange has some slack in it -- need to measure for comparison's sake. How much slack is normal? Trans in neutral, turning driveshaft back and forth.

I realize this slack can be from the gear backlash setting, clearances in the differential, and clearance between the carrier housing and the splines of the axle shafts.

When you re-lubed the slip yoke, did you brush it on the splines or did you use the zerk fitting? Also, did you remove all of the excess grease at the bottom of the yoke where it builds up?

The only drive line clunk I've ever had is when I used the zerk fitting on the flip yoke to grease it. Once I stopped doing that and just brushed the grease on the splines, my clunk has never returned. It should be noted that my clunk would only happen when going between D and R, not coasting like your situation.

If the driveshaft isn't binding up, it's probably something with the 3rd member like excessive backlash. That's my guess at least.

I've noticed this spontaneously on my rig as well. Subscribed to see what comes of this thread in the near future!
Like you, @JZiggy , I only notice it when coasting in first or second, then accelerating slowly. It's just a faint clunk every once in a while, but it is there.

Thanks for the responses guys! I did in fact remove my rear slip yoke and fill/brush with the blue Ford PTFE grease made for the application. I went so far as to fill a small grease gun so I could reapply at the zerk. I think that grease chamber behind the splines is pretty full... maybe that is the problem, I should take the yoke back off and remove some so it has some more space to move?

Here's the details of my greasing process https://www.toyota-4runner.org/3308038-post264.html

As Jordan knows, I've tried to figure out a solution for this problem and I thought I had found the answer with removing the slip yoke and manually greasing it with the Ford XG-8 grease. At first, my driveline stayed clunk-free for almost 10k miles. But, the manual greasing of the shaft became less clunk-free. When it got to the point that a manual greasing of the slip yoke only got me around 1k clunk-free miles, I gave up and just embraced the clunk.

At least for the clunk I have in my 2000, I don't think this has to do with the 3rd member. The clunk I have actually makes it sometimes feel somebody rear-ended me at a stop light by rolling into my rear bumper. I don't think a bind in the 3rd member would cause this. But, it makes sense that the slip yoke becoming unstuck on the main driveshaft would give you a bump feeling.

I would remove all of the grease pooled at the bottom of the splines. Only the splines themselves need grease and having the bottom filled up causes binding and does nothing to keep the splines greased.

The other thing I did that I forgot to mention was I completely removed the zerk fitting on the slip yoke and left it off. I figured since I wont ever be using it and it will allow air to escape when the yoke is sliding in and out.

Haven't had a single clunk in 2 years.

At the very least, you'll want to remove any grease that is pooled up at the bottom and leave the zerk fitting off for testing purposes. If the clunk is gone, that was your problem. If she's still clunking, you know to look elsewhere.

Good luck

We discussed this before and I did what you suggested above but it didn't work for me. I suspect that my driveshaft was improperly lubricated for such a long time that excessive wear occurred to the splines and it's more prone to bind.

This got me thinking about pressure relief valved zerks. Unfortunately no one makes one for a little M6 application like this.

I'll clear some grease out to make a decent air pocket and see if that helps. The more I think about it having a bunch of grease in there is going to prevent the slip yoke from actually moving in the "shortening" direction.

All that being said -- can anyone else verify for me much angular slack their rear pinion has? I just want to rule that one out too as a culprit.

The closest I could find in the FSM was ring gear backlash, which I suppose can be converted to angular displacement at the pinion flange...

That exercise will be left up to the reader unless I take the time to draw out the geometry.

-Charlie

Well, that got me to 0.5 degrees. I know it’s more than that in actuality.

I would agree with that. I'd guess most of the (good, working) diffs I have seen are more in the 5 degree range? Hopefully somebody else can chime in.

-Charlie

Some updates: this weekend I pulled the D/S yoke off again and cleaned out the mountain of grease inside. There was enough grease in there to limit the inward travel of the yoke. I went with the @thegipper method and left the cavity empty just coating the splines with fresh XG-8. I left the zerk in but am thinking about options to keep the system sealed while allowing free movement of air...

Clunk's still there. I'm starting to think this is not a driveshaft issue.

The pinion slack I could feel coming from the gear setup was actually very minimal, less than 1/16" on the OD of the flange. I'm estimating a couple of degrees at most. There was some more slack in what felt like the axle shaft splines... with the rear lifted and holding the pinion still I could spin the wheel back and forth a bit and make it "clunk". Maybe the TrueTrac carrier is machined with more tolerance than the factory unit?

OP have you checked your rear UCA and LCA bushings and bolts. Get under the truck put it in park and rock the truck back and forth with your legs and pay attention at the LCA and UCA, also look at the rear u-joint. If it moves up and down, your bushings are no good or the bolts are lose. Just check that!

While rocking the truck back and forth. There should be absolutely 0 play on the ends of the arms. Easily diagnosed by putting your hand on the arm on each end to feel for play.

Interesting. I also have a TrueTrac but I don't have any clunking issues. Hopefully you can figure it out, good luck!