After installing the Rancho lift and new front 1350 JE REEL driveshaft on our 2023 JLUR, I noticed an audible humming noise while driving 65-80 mph. It wasn't super loud, and you could not feel a vibration. Just an annoying hum. It was driving me crazy! LOL! (Most people probably wouldn't have noticed or cared) It was really hard to determine if the hum was coming from the front or the rear although Steph thought it was coming from the rear of the Jeep.
Since the front driveshaft does not spin while in 2WD, I knew the noise couldn't be coming from the front DS. So, I decided to remove the rear DS and drive it in front wheel drive. (Not fun I might add!) Low and behold...no more hum! With this new information, I thought maybe the factory shaft doesn't like spinning at these new angles. By eye, everything looked fine to me. However, using an angle finder, I did see a 2-degree upward variance between the pinion flange and driveshaft flange. I measured a stock JL and found a rear DS upward variance of 1.2 degrees. With this new information, I thought maybe changing the pinion angle to 1.2 degrees will make a difference.
To get the 1.2 degrees variance, I had to lengthen the rear lower control arms about a 1/2 inch. This dropped the rear pinion slightly bringing the new angle to 1.2 degrees. Went for a drive and no difference.
I knew eventually, I would be replacing the rear driveshaft with a 1350 double cardan but didn't want to mess around with the pinion crush sleeve. After searching the Internet for a solution, I discovered that Neapco makes a flange that will bolt up to the factory pinion flange. Here's a link to the actual part.
https://neapcoparts.com/n3-2-jl01-driveshaft-flange-yoke/
I checked JE REEL, Adam's, and a few other driveshaft websites and none of them offered this as an option. However, I did find a driveshaft company (full torque driveshafts) located in Idaho that does offer this flange as an option. I decided to call JE REEL to see if they heard of this Neapco flange and much to my surprise, they said they can build a shaft with this new flange.
Anyway, long story short, I ordered a new rear DS from JE REEL and installed it today. I'm happy to report that noise is almost completely gone now. I'd say there's about a 95% improvement. The other 5% could just as well be in my head...
Here's a few pics. Hope this info helps anyone suffering from bad vibrations/humming.
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