Loud knocking under load in 4WD

[4wd man]

Hi guys, I heard some loud knocking sounds from underneath the JK last time I went wheeling. The first time, it happened while I lost traction climbing a steep hill. As the tyres were spinning and the rev counter was around 3000-3500rpm (low range no lockers and then with lockers) there was a constant loud knocking sound. On the second occasion I had both lockers on and was spinning all wheels on a slippery steep rocky incline again under constant load at around 2500-3000rpms. On the third occasion I was going up a steep muddy hill (low range no lockers) and the noise got louder as I increased the revs. I ruled out the BLD causing the noise since it was not kicking in as the yellow dash light was not on in these particular occasions. Other times the BLD kicked in at lower revs on the same trip, there were no issues.
I crawled underneath today to try to see if I can figure it out. The noise is very similar to the one I heard except much louder when I rotated the front driveshaft back and forth (understand that when under load the driveshaft will only rotate in one direction) which seems to have quite a bit of play in rotation (as a rough guess around 5mm total) but none along its length and the noise seems to be around the front end and not the transfer case end. I am not a mechanic so I have no idea if that amount of play is normal. The rear driveshaft on the other hand has no movement at all as if its fully welded to the diff and transfer case. On the road, it's smooth as with no vibrations or noises whatsoever at all speeds and under all loads.
It's a 2012 2-door manual Rubi, 19000km, AEV 2.5" lift with geometry correction brackets, stock size tyres and still under warranty. I drained and refilled all diffs, transmission and T/C recently and they were clean with no broken bits. I will take it to the dealership this week but since they won't be able to replicate the noise while driving it on the road I want to make sure I can get as much information from you guys in case I am told that they looked at it, drove it around the block and couldn't find anything wrong with it. Any advice and feedback much appreciated.

[trbn8r]

Check ur uni joints mate..... Sounds like one or both are buggered........

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[Fruju]

You will most likely only hear this noise when climbing. The front becomes unweighted and as you try to maintain forward momentum by increasing revs the sound is likely to be heard.
What is happening is the unweighted front axle is gaining traction then breaking it then trying again. It is moving forward and backward and also up and down as it is trying to gain traction. What is holding it to the vehicle? The control arms. So this noise is created by the shock from the axle hop being transmitted back through the control arms to the chassis.
When watching vehicles that this is happening to it looks like they are about to break an axle or a uni.
So when you hear it, I would suggest easing off the revs.

[trbn8r]

Originally Posted by 4wd man

The noise is very similar to the one I heard except much louder when I rotated the front driveshaft back and forth (understand that when under load the driveshaft will only rotate in one direction) which seems to have quite a bit of play in rotation (as a rough guess around 5mm total) but none along its length and the noise seems to be around the front end and not the transfer case end. The rear driveshaft on the other hand has no movement at all as if its fully welded to the diff and transfer case.

This relative mmovement points to a buggered uni joint, possibly a missing cap. Check it before it buggers up the axle and stub ears as well and then it will be an expensive exercise....... My unijoints went just under 30000 ks. So it wouldnt be a big surprise.

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[4wd man]

Thanks guys. Just got a call from the dealer. Apparently the 'aftermarket' suspension was not installed correctly and that's what causing the issue and will therefore not be covered by warranty and they won't touch it. I find that hard to believe so I'll ask a few more questions when I pick it up this afternoon.

[MightyMouse]

Dealer Speak for "screw you"........

[4wd man]

OK, just got back from the dealer. I was told that they checked all U-joints and driveshafts for movement and all OK. They reckon both front shocks are leaning to one side and therefore not fitting correctly. My understanding is that is because I don't have an adjustable front trackbar hence the front axle is slightly offset. According to AEV not really necessary for the 2.5" kit since the offset is only around 6mm. I was also told that not all suspension components were changed which can cause incorrect fitment and alter suspension operations. Well, the kit is complete and I also have the front control arms brackets installed. Yes, I also had to pay $150 for that 'report'. Not sure what my options are now. [IMG][emoji15][/IMG] Thoughts???