I just read all 8 pages of this. This issue is insane. I have a 2020 Classic 1500 Tradesman, 2x4. High pitched vibration right dead at 1400 RPMS. Soon as I get above 1500 or below about 1300, it goes away. Cannot reproduce in park. Only happens under load. Vibration isn’t the best description..it’s very high-pitched & creates a harmonic droning. Can hear it & feel it in the floorboard, wheel & pedal. Most passengers don’t notice it. This is what I have done:
1. Opened rear-end. No more metal than you'd expect. Backlash .09. Replaced spider gears. Replaced rear wheel bearings & seals.
2. Sent driveshaft off, got new joints, bearings & balance. Made it a little better, didn't fix it.
3. Replaced transmission with a 52k trans off eBay from a wrecked Ram. Used my old computer. Improved some, didn't fix it.
4. Bought brand new driveshaft from Mopar. No change.
5. Adjusted 2 piece shaft angles by lowering carrier bearing & buying adjustable upper control arms. No change.
6. Replaced MDS lifters with OEM Mopar lifters. Replaced camshaft, VVT sprocket, chain & added a high volume oil pump. Not MDS related. No change.
7. Mounted camera under truck in 3 different spots--looking at carrier bearing, pinion & driver motor mount. Didn't spot anything obvious. Camera did pickup a bit of the "drone" (audibly not visually) when mounted above the pinion, though.
It's worse the colder it is. Metal shrinks in the cold. If I am driving through a roundabout with a little speed going left & it hits that RPM range it is 5x worse. It goes from the cell phone buzz to something obviously isn't right. Like a whipping feeling. Hard to explain, but worse going left. Not worse going right.
The amount of work I have done to try & fix this issue is insane. The only thing left is the rear end. I see some people said front wheel bearings &, at this point, I'm not above trying anything but being RPM specific & getting worse in turns just seems like rear end to me..
It's cold as heck here right now so if it will make it through the winter like this, I'll probably just keep trucking it for now. Spring time I'll probably swap the rear end. I may try putting a driver's front wheel bearing on it between now & then but my hopes aren't high for that. Feels like it's in the driveline to me.
I got this truck with 74k. I know why they traded it in, now. Lol. If anybody has resolved this or tried rebuilding/swapping the rear end, speak up please.