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Drivetrain Noises


Tungsten
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At times when driving at certain RPMs and speeds, I get some crazy sounds like tapping and wobbling heard from the drivetrain. Usually it happens when the engine is under heavy load like climbing a hill in overdrive or in third. The noise most often occurs around 40 mph at 2500 rpm and 60 mph at also the same rpm. If I throw it into neutral then the noise goes away. I have already replaced the U-joints and that has alleviated the problem but the sound is still there. With the new U-joints the noise no longer happens at certain speeds that it used to happen on but still happens on some like 40 mph. What could be the next step in diagnosing this? I am thinking about putting the truck on jack stands and just watching the driveshaft. Is it possible that a weight has fallen off the driveshaft and that is throwing it out of balance? I already checked for lateral play in the shaft and there wasn't any that I could notice. There is a little lash in the gears when in neutral but that's normal.

 

Any input should help. Thanks.

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So, it sounds like it is engine RPM dependent, not wheel/drive train dependent? It sounds more mount related to me but hard to tell from here.

 

Be careful with it in the air. I have done the same and it diagnosed U joints for me but make sure it is well supported, especially if you are reving/shifting.

 

B

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I can pop it into neutral when it's doing the noise and it instantly goes away. It doesn't change with RPMs either. I'm thinking it could be mount related too. Maybe the transmission or engine mount just slightly changes some angle enough under load for the shaft to vibrate.

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If you believe it's an engine mount it would likely be the driver side as this is the one the engine torque tends to pull apart. One way to check is to put in gear and hold break while giving it a little gas. Have some watch the engine for excessive movement. You might be able to see it yourself through the gap when the hood is up, but maybe not so have a second set of eyes is helpful. Just make sure they stand to the side when doing this.

Edited by andreus009
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Yeah I'm just exploring all the possibilities now. I'm not ruling out input or output bearings either. The driveshaft doesn't have any lateral play in it but I'm going to give those bearings a second look again too. Another possible problem I saw on a Jeep forum was the rear control arm bushings having enough play in them to change the pinion angle. Also I'm going to try and make a video and look at the driveshaft in motion.

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Well if it is 4WD its definately not a carrier bearing.

If it sounds like it is coming more from the rear it could be the front drive pinion bearing where the driveshaft and differential meet up. could be critically low fluid in the diff too if from the rear.

If this is a MT tranny and it sounds like it is from teh front it could be the rear main shaft bearing making noise, again could be low MT fluid.

There are not any weights or anything on it. If the propeller shaft is bent or dented too much it will wobble.

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  • 2 weeks later...

Ok I solved this problem. It was pretty interesting. I got it to a shop and they got it up on a lift and saw that some of the wheels were dragging more than others even after running the truck in 4WD for 5 minutes without applying the brakes. Surprisingly the driveshafts were perfectly in balance. So one of the mechanics asked me about the flex hoses and I just went out and got new ones made by Nichirin. Not everyone agreed with that theory in the shop but I asked them to do it anyway. Finally when I went there to get them replaced, after they changed them I went out to test it and what do you know the random occurring noise was no longer there. Basically I had slight brake drag on 2 of the 4 calipers from aging and possibly failing flex hoses.

 

The other fun problem I noticed was that my tires started developing run out. The tires had a slight side to side shake on the lift when being run. From my online research it seems to be normal. It's not that bad where it's undriveable but it is just ever so slightly noticeable at some speeds.

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I don't either but you know what's funny is the new U-joints and new brake lines completely eliminated it while driving. The noise isn't gone though. Looks like I got excited too early. It's still there but only when downshifting into 2nd and sending the engine to 4000 rpm when trying to engine brake. I could hear it come on and go away as the engine revs up to slow down. It's like shift to 2nd then rev then grind then it just goes away. It's crazy and now I'm afraid that it might be transmission related. Those clutch packs could be slipping and making that sound. Going to try and get a video tomorrow.

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If you're talking about that cylinder around the shaft I don't have it. I don't even know if it's clutch related or not because there is no slippage I can feel and the gears shift nicely. I just hate things that are so intermittent and hard to diagnose.

 

My brakes are perfect. The rotors are smooth as glass. They only have 2000 miles on them. They were recently changed.

Edited by Tungsten
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I don't either but you know what's funny is the new U-joints and new brake lines completely eliminated it while driving. The noise isn't gone though. Looks like I got excited too early. It's still there but only when downshifting into 2nd and sending the engine to 4000 rpm when trying to engine brake. I could hear it come on and go away as the engine revs up to slow down. It's like shift to 2nd then rev then grind then it just goes away. It's crazy and now I'm afraid that it might be transmission related. Those clutch packs could be slipping and making that sound. Going to try and get a video tomorrow.

I really wouldn't advise engine braking with an automatic like that. Having it locked in one gear and letting it run up and down in RPM is one thing but manually downshifting is really just putting a significant strain on the tranny. Brakes are far cheaper and easier to replace... ;)

 

B

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It says in the manual that it is ok to downshift like that "when engine braking would be advantageous", their words, not mine!

 

I still never do it because why wear the tranny more than necessary when brakes are dirt cheap to change. Only time I do it is on steep trail descents in 4 low.

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Normally I wouldn't downshift from like 40 mph into 2nd but I wanted to stress the transmission on purpose to see if any noises came out of it for diagnostic purposes. The 1st and 2nd gears actually have a deceleration clutch so you can cruise down a hill in them all day long. I prefer riding 2nd gear down long hills with 30 mph speed limits or lower because it avoids overheating the brakes and boiling the fluid. I guarantee that it doesn't do anything bad to the transmission if you slow down to around 25 mph first and then engage 2nd.

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I think I found it. Looks like the damn exhaust crossover is hitting on the frame again or possibly the mid-pipe where it gets close to the transmission bracket. I think I'm going to check the transmission mount again. It just happens every so often and it sounds like something is grinding but it's really just the pipe buzzing when the engine starts shaking around under load enough. I did have a tapping sound from the drive-train earlier too but that seems to have completely disappeared with new brake flex hoses. Now I did have some issues with the shifting and engine acting funny earlier but it rarely ever happens and I think it's just the knock sensor being triggered when the noise gets a little too loud. It wasn't happening before so I think it's just a mount getting a little loose.

 

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Forgot to mention but I also changed the hubs to manuals. I wanted to do it anyway and thought maybe the autos went bad or something. They didn't but I do love the manual hubs now.

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