Driveline Noise

[ChadsTJ]

Hi all,
I recently installed my Rubicon Express SuperFlex Adjustable LCA's. My TJ is on a 3.5-4" (not sure i bought it lifted) Rancho lift with stock UCA's and the owner before me had never installed control arms after lifting it. With the stock arms believe it or not I had no noises. Post install I am getting driveline whining from about 2-5th gear at higher speeds/rpm only under acceleration. I understand the pinion angle is important, so I readjusted the arms to the stock length and I am still getting driveline noise. It doesn't make sense how it makes the whining still even after putting the arms to the exact length that was on it. Any ideas?

 

[Chris]

Measuring length of the control arms is absolutely pointless. I wish people would stop doing that.

What matters is that your axle is centered under the vehicle and that at full bump your lower spring perch is centered with the upper jounce bumper.

Once that is set via the lower control arms (again, throw the tape measure out, it doesn't matter one bit what the numbers are), then you use the upper control arms to set your pinion angle.

During this entire process you should not even have a tape measure nearby as it is not necessary. The only number that matters here whatsoever is your pinion and driveline angle, and that doesn't involve a tape measure.

Post photos up of your driveline angle so we can see for ourselves.

 

[Rubicon88]

Think hard...

What all things did you disturb when you started messing with it???

 

[Blackjack]

Hi all,
I recently installed my Rubicon Express SuperFlex Adjustable LCA's. My TJ is on a 3.5-4" (not sure i bought it lifted) Rancho lift with stock UCA's and the owner before me had never installed control arms after lifting it. With the stock arms believe it or not I had no noises. Post install I am getting driveline whining from about 2-5th gear at higher speeds/rpm only under acceleration. I understand the pinion angle is important, so I readjusted the arms to the stock length and I am still getting driveline noise. It doesn't make sense how it makes the whining still even after putting the arms to the exact length that was on it. Any ideas?

Did you install the arms with the Jeep on the ground or with the axles drooped? RE arms are not the best choice from an NVH standpoint as one end effectively is a rod end and the newer arms that do not use a clevite bushing have a pretty high durometer. Also did you make any other changes at the same time? Mess with the belly pan or anything like that?

 

[ChadsTJ]

Did you install the arms with the Jeep on the ground or with the axles drooped? RE arms are not the best choice from an NVH standpoint as one end effectively is a rod end and the newer arms that do not use a clevite bushing have a pretty high durometer. Also did you make any other changes at the same time? Mess with the belly pan or anything like that?

I adjusted them at normal ride height not drooped and sitting on the ground. I have had no vibrations whatsoever. Just slight pinion whining. All I’ve messed with is the arms. It also has an SYE

 

[ChadsTJ]

Measuring length of the control arms is absolutely pointless. I wish people would stop doing that.

What matters is that your axle is centered under the vehicle and that at full bump your lower spring perch is centered with the upper jounce bumper.

Once that is set via the lower control arms (again, throw the tape measure out, it doesn't matter one bit what the numbers are), then you use the upper control arms to set your pinion angle.

During this entire process you should not even have a tape measure nearby as it is not necessary. The only number that matters here whatsoever is your pinion and driveline angle, and that doesn't involve a tape measure.

Post photos up of your driveline angle so we can see for ourselves.

---

Sorry as I just saw this. Thank you for the response!
Here is the pic.
I am also on stock uppers. So I am limited on adjustment. I would just like the noise to go away as I know it can lead to premature wear.

 

[Chris]

Well your biggest mistake is stock uppers. The lowers are used to set the wheelbase, nothing more, nothing less. The uppers are used to dial in the pinion angle. By doing it the way you are doing it now with adjustable lowers you're compromising wheelbase (and the axle being correctly centered under the vehicle) to make-up for pinion angle.

I can tell your pinion angle is too low. The pinion needs to be raised up higher, and you're going to need to either play a game of trial and error (guessing the pinion angle, then taking it for a drive after each adjustment), or you're going to need a digital angle finder to measure the angle exactly. The pinion should be 1-2 degrees lower than the driveshaft at ride height.

 

[Goatman]

Are you absolutely sure the whine is from the rear driveshaft? Try pulling the front shaft and see what happens.
Also, are the jam nuts on the control arms good and tight? Any rotation there could cause noise.
I am no expert driveshaft angle guy, and am looking at the pics on my phone, but it looks like you need to lower the rear pinion a bit. It will rotate up under load making it (to my eyes) over rotate the pinion. Also, on the transfer side it seems the D/C it at two different angles. The one joint near the transfer seems to be doing all the angle while the shaft side Ujoint appears to have zero angle. A bound up Ujoint, or possibly the shaft itself is either not extending enough or is too short.

 

[TurboTJ]

I think the angles on the DC are probably the same. It just looks like they may be different because of the camera angle. To my eye, the pinion angle might be a touch too high though.

Could the gear whine just be due to the fact the joints on the RE arms are probably a lot stiffer than the relatively plush OEM bushings, transferring more of the noise to the frame and tub?