Please Help Me Diagnose Gear Noise & Vibration Over 30MPH

[BradyW]

My 2005 LJR has developed a whining noise that starts around 30mph and transitions to howling/growling over 50mph. The sound is present on the road, and when the Jeep is on jack stands with the front driveshaft stationary. The sound is loudest when lightly applying the throttle off idle or just after letting off the throttle. The sound feels louder inside the Jeep than it does outside and the noise seems to be coming from directly under the cup holders.

My rear pinion angle is 0 degrees to the driveshaft, and the sound does not appear to be originating from the driveshaft when standing outside the Jeep on jack stands.

My thought is that it's either a bearing or a gear issue inside the transfer case, but if someone else has heard this before and knows what to do please correct me!

 

[AndyG]

Remove the front driveshaft and see what happens

If the cardan joint in the shaft is failing is can do catastrophic damage to the jeep

 

[BradyW]

Remove the front driveshaft and see what happens

If the cardan joint in the shaft is failing is can do catastrophic damage to the jeep

The noise is the same when the Jeep is on jack stands with the front shaft/wheels stationary as it sounds when the Jeep is on the highway. The video posted is on jack stands in my driveway.

Engaging 4WD on jack stands changes the harmonics of the noise slightly but doesn’t change the severity or volume.

The noise appears to be either in the rear shaft or the transfer case. I guess I could remove the rear shaft and try it again in 4WD and see if the noise persists.

 

[AndyG]

Well first it’s pretty hard to hear anything from the video and understand want to listen for- Noise videos are like that a lot of times.

Transfer case chain noise is not out of the question- but we don’t see it a whole lot.

I am constantly amazed at how visible everything can be under these things and how hard it is to chase down a noise.

You can get some noises around the fly wheel with some automatics but that may be another story-

I think you’ve got the right idea - pro shops pull a shaft most everytime

Just don’t rule out the front- I’m not saying you have a problem but it is the one that you do not want to see go out at speed.

 

[BradyW]

I have done some additional testing and now believe the noise and vibration are coming from the rear differential. The sound becomes audible around 20MPH and hits the resonance frequency of the tub between 30-40MPH. Over 60MPH, the gear noise sounds like 737 engines on take-off.

The gears were replaced to 5.13's around 1000mi ago. The noise started around 300mi ago; it was not present immediately after the re-gear or during the break-in period, which I followed religiously.

Does this sound like a pinion bearing or ring/pinion interaction to you all? If not what do you think is the issue?

• Pull rear driveshaft: Noise/vibration completely gone.
• I replaced the rear driveshaft with a new Adams 1310/1330 drive shaft. There is absolutely no change in noise/vibration.
• If I place the rear axle on stands, such as in the video below, the noise and vibration are still present, so I don't believe the front driveshaft/axle is contributing to the problem.
• The noise/vibration is equal with overdrive turned off or left on.
• Adjusting the rear pinion angle anywhere between +1 to -3 degrees to the drive shaft does not change the frequency or volume of the noise/vibration. (Thank you, Savvy double adjustable control arms, for the easy testing on this!)
• When you place your hand on the rear diff cover you can feel vibration that coincides with the gear noise that you can hear in the video below. This leads me to think that it's a problem between the ring and pinion gears, but I'm very inexperienced in diagnosing these kinds of things.

 

[Jerry Bransford]

Sounds like the gears weren't set up properly or they simply overheated during the break-in process despite your having been careful.

Was synthetic or conventional gear lube used during the critical break-in process? I made the mistake of using a synthetic gear lube (against my better judgement but it was pushed on me) during my last gear break-in and despite a very careful break-in, the rear gears still got too hot and started making noise. The gear specialist I took it to to have the rear gears replaced under Revolution Gear's warranty took one look at them and literally pointed his finger at me and accused me of having use a synthetic gear lube. He was right and he filled the axle up with a conventional after he was done for the next break-in. I made sure I refilled it with a conventional at the 500 mile mark.

This is why gear manufacturers like Revolution Gear strictly recommend conventional gear lubes during the critical break-in process. After they're broken in conventional vs. synthetic doesn't matter as much but it's important during the break-in process for aftermarket gears that haven't yet been work hardened against each other.

This is what Revolution Gear says about the type of gear lube they recommend: "The recommended gear oil is an 80W-90 or 85W-140, non-synthetic, GL5 grade or higher from a name brand" per their webpage at https://revolutiongear.com/blog/ring-and-pinion-break-in-procedure/

 

[mrblaine]

I have done some additional testing and now believe the noise and vibration are coming from the rear differential. The sound becomes audible around 20MPH and hits the resonance frequency of the tub between 30-40MPH. Over 60MPH, the gear noise sounds like 737 engines on take-off.

The gears were replaced to 5.13's around 1000mi ago. The noise started around 300mi ago; it was not present immediately after the re-gear or during the break-in period, which I followed religiously.

Does this sound like a pinion bearing or ring/pinion interaction to you all? If not what do you think is the issue?

• Pull rear driveshaft: Noise/vibration completely gone.
• I replaced the rear driveshaft with a new Adams 1310/1330 drive shaft. There is absolutely no change in noise/vibration.
• If I place the rear axle on stands, such as in the video below, the noise and vibration are still present, so I don't believe the front driveshaft/axle is contributing to the problem.
• The noise/vibration is equal with overdrive turned off or left on.
• Adjusting the rear pinion angle anywhere between +1 to -3 degrees to the drive shaft does not change the frequency or volume of the noise/vibration. (Thank you, Savvy double adjustable control arms, for the easy testing on this!)
• When you place your hand on the rear diff cover you can feel vibration that coincides with the gear noise that you can hear in the video below. This leads me to think that it's a problem between the ring and pinion gears, but I'm very inexperienced in diagnosing these kinds of things.

Your rear gear set is toast, fix it.

 

[mrblaine]

Sounds like the gears weren't set up properly or perhaps they overheated during the break-in process despite your having been careful.

Was synthetic or conventional gear lube used during the critical break-in process? I made the mistake of using a synthetic gear lube (against my better judgement but it was pushed on me) during my last gear break-in and despite a very careful break-in, the rear gears still got too hot and started making noise. The gear specialist I took it to to have the rear gears replaced under Revolution Gear's warranty took one look at them and literally pointed his finger at me and accused me of having use a synthetic gear lube. He was right and he filled the axle up with a conventional after he was done for the next break-in. I made sure I refilled it with a conventional at the 500 mile mark.

This is why gear manufacturers like Revolution Gear strictly recommend conventional gear lubes during the critical break-in process. After they're broken in conventional vs. synthetic doesn't matter as much but it's important during the break-in process for aftermarket gears that haven't yet been work hardened against each other.

Regardless of who says what, I've had several front Rubi 44 gear sets lock up due to the use of conventional gear oil for the break in. This was after I explicitly stated to not fill them with oil, let me do it and if they ignore that, then use at least a semi-synthetic or they'll be fixing a set of gears. They had really sad looks on their faces when I had the tow truck drop off the rigs with the front tires locked up.

 

[BradyW]

Your rear gear set is toast, fix it.

Thank you! I didn’t want to take it back to the shop for something I could adjust out at home. That threshold has been passed. I’ll call them tomorrow.

 

[BradyW]

Sounds like the gears weren't set up properly or they simply overheated during the break-in process despite your having been careful.

Was synthetic or conventional gear lube used during the critical break-in process? I made the mistake of using a synthetic gear lube (against my better judgement but it was pushed on me) during my last gear break-in and despite a very careful break-in, the rear gears still got too hot and started making noise. The gear specialist I took it to to have the rear gears replaced under Revolution Gear's warranty took one look at them and literally pointed his finger at me and accused me of having use a synthetic gear lube. He was right and he filled the axle up with a conventional after he was done for the next break-in. I made sure I refilled it with a conventional at the 500 mile mark.

This is why gear manufacturers like Revolution Gear strictly recommend conventional gear lubes during the critical break-in process. After they're broken in conventional vs. synthetic doesn't matter as much but it's important during the break-in process for aftermarket gears that haven't yet been work hardened against each other.

This is what Revolution Gear says about the type of gear lube they recommend: "The recommended gear oil is an 80W-90 or 85W-140, non-synthetic, GL5 grade or higher from a name brand" per their webpage at https://revolutiongear.com/blog/ring-and-pinion-break-in-procedure/

I’m not sure what type oil the shop put in the diffs. They replaced the oil after the break in inspection and I haven’t touched the rear diff since.

I’ve had the front diff cover off since the inspection and refilled with valvoline fulll synthetic. No issues with it so far, but it’s also under lighter duty than the rear.

I will update back after the shop takes a look.

 

[BradyW]

The shop replaced the rear gears and pinion bearing under warranty. I got the Jeep back yesterday and the howling is gone! I celebrated by installing some Motobilt rocker tubes this morning. Thanks for the help, everyone!

 

[ChasUGC]

I would check to make sure you have oil in your transfer case. I don't know how it happened, but mine went dry. One day, my Jeep just stopped moving. It would start up and the engine would run, but it wouldn't move. Transfer case oil is just something that we never normally check, and vehicles burn oil. Mine was burned dry after 20 years. Now I have my differential and transfer oil levels checked every 3 years. I believe this was mentioned in my owners manual as a later maintenance.

 

[BradyW]

I took it back to the shop that did the re-gear and they replaced the gears and bearings under warranty. The rear diff is silent now.