Calling driveline experts: clunk clunk at slow speed?

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Jun 9, 2017
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Denver, NC
I have developed this clunk clunk clunk at very low speed as I approach a stop sign, etc. Only when the clutch is depressed or the rig is in neutral. It sounds like the drive shaft is locking and unlocking semi-rapidly and corresponds to speed (i.e. as I slow down the clunks get farther apart until they stop).

You can hear it in this video - the clunking begins at about the 6 - 7 second mark. Anyone have any idea what this is?

Thanks!

 
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Can’t tell if it’s just driving or when your sitting idle as well? Sounds like a flywheel bolt is coming free and hitting the clutch disc if it’s happening when your at idle
Not at idle - that's smooth as silk. Just in motion - definitely a drive line issue of some sort. I will dive under this pm and have a look at the u-joints
 
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Ok folks - I don't see any obvious issues with the u-joint. Here are a couple of videos:

This one shows the entire rear driveline - the clunk I'm able to make you hear at 12 seconds and following is for sure what I'm hearing as I decelerate.


This one shows the joint with the most play - maybe 1/32":


Any additional advice is appreciated!
 

mattcamp

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When you clunck the driveshaft back and forth is it in gear or neutral? Are your rear wheels on the ground? Is this the one with ARB lockers and Marlin case? Sorry for all the questions, it's just that's a lot of clunk going on..... if it is in gear, try low and see if it still does it.
 
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When you clunck the driveshaft back and forth is it in gear or neutral? Are your rear wheels on the ground? Is this the one with ARB lockers and Marlin case? Sorry for all the questions, it's just that's a lot of clunk going on..... if it is in gear, try low and see if it still does it.
Thanks for the questions Matt!

Transmission was in neutral. Yes, this one has the marlin low gear and ARB's. Had one tire off the ground for the clunk experiment. I will go out and repeat in low gear this evening.
 
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Ok, tried both low and high gear and the slop seems the same (though harder to turn in low gear). Here are a couple of vids:

Low gear:

High gear:

I'm thinking it might be the third member but not sure - any other ideas on how to trouble shoot this?
 
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I disconnected both drive shafts and the front and rear pinions turn about the same. Xfer case feels tight. U joints seem tight.

I rolled the truck out of the garage in neutral and I could actually see the driveshaft stop and start again with each "clunk" sound. Couldn't recreate it quite as well on the video below but have a look (and listen). Other interesting thing is, when the truck rolls slowly forward, with engine off, in neutral, I can actually "feel" the trucks momentum slow with each clunk (i.e. I shift slightly forward like I tapped the brake a bit).

Any ideas? Next step was going to be to pull the rear drive shaft and drive it front only - at least to start isolating variables (in this case the rear third).

 
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That is a great video. The problem is they want you to mark the shafts BEFORE removal. What if you forgot to that ? How do you create phasing.
you make sure that the joints on each end of the shaft are in the same position. IE if you were to draw a single line from one end of the shaft to the other, it would go through the same section of each joint
 
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Yes, in phase - tried it both ways - good thought!

In the last video it appears that the flange on the pinion is bent and hitting the axle housing at the same tempo as the clunk.
I saw that too - checked the run out on the pinion as best I could this am and it doesn't appear excessive at all - especially since there's no great place for the tip of the dial indicator to ride and the flange is rusty. Have a look at yet another video:

 
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One time there was an intermittent clunk coming from the rear third member on my FJ40. Turned out a couple bolts worked loose on the ring gear and would hit the edge of the banjo part of the axle housing.
 
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