Peterbilt / 6NZ Vibration

What part is worn? The splines where the disk are? Why do think this?

 

if you turn the wheel one way it goes away it sounds like a chasis vibration i had a pete once that did that ended up being a bolt on the block that would hit the exhaust pipe when you would torque up the motor.

 

Hi im having same problem whanted to know if you found problem

 

I sure hope someone can diagnose this one.
Very power sucking vibration in 03 Pete 379 / 6NZ.
New tranny , clutch, input shaft, throw bearing, balanced driveline, new front diff / power divider, all tight from front to back. Only occurs under load ( empty or loaded..Empty I'm 60,300 lbs. Loaded I'm 140,000+ Lbs)
Oil analysis sent to CAT which I do every oil change at 10,000 miles. Still awaiting results but always comes back no issues.
Getting a humming wine noise from front end past weeks so I think I'll get wheel bearings checked.
Noise never happens in bottom set of gears ( 1 - 10 ) only starts after I split and start over (11-18) and although I run engine at / around 1500 RPM tops for the most part, and the odd time to 1600 RPM when merging onto a big road heavily loaded (140,000 Lbs +) , I'm finding the vibration increasing beyond 1400 RPM in top gears under heavy torque, so I don't rev it over 1500 RPM regardless.
Any info would help.
P.S....for unknown reasons, I can rev beyond 1500 no probs at all, zero vibrations etc., but it's far and few between and short lived.
Help!!!

 

How old is your fluid damper on front of engine. Original??
If so I'd start with that. Replace it.

 

JUSST TO CONFIRM. YOU ARE TALKING ABOUT THE VIBRATION DAMPER...RIGHT..?
IF YES. I WAS ALSO CONSIDERING THAT, IM SURE ITS ORIGINAL. IVE HAD THE TRUCK 2 YEARS NOW AND WENT OVER THE ENTIRE LIST OF MAINTENANCE RECORDS (PRIOR OWNER WAS GREAT AT KEEPING RECORDS ) AND NOPE, I HAVENT SEEN THAT REPLACED.
I DID ALL WIRING HARNESSES (ENGINE AND INJECTOR) ALL SENSORS, FUEL PRESSURE REGULATOR, THROTTLE POSITION SENSOR, FUEL LINE (SUPPLY) AND DIVIDER VALVE AND DIVERTOR VALVE, FUEL PUMP, PRIMARY FUEL FILTER HOUSING (WAS SUCKING AIR) FRONT DIFF/POWER DIVIDER, TRANNY DONE LAST WEEK, NEW CLUTCH /THROW BEARING AND INPUT SHAFT, PLATINUM WARRANTY STILL ON ENGINE, RAD AND INTERCOOLER BY PRIOR OWNER 3 YEARS BACK, ALL MAXI'S /BRAKES AND STEER AXLE POTS, ETC...ETC... (I STAY ON TOP OF EVERYTHING, AND HATE GIVING MY HARD EARNED TO THE FEDS SO I STAY CLOSE WITH MY ACCOUNTANT.
Weird is the vibration can disipate or go away all together. Example; If im getting on the big road and its on a mild down grade, regardless of how heavy i am and the hard torque needed to get up to speed, the down grade seems to help in some way. Vibration is darn near not there at all. But soon as im pulling uphill, empty even, and im still in upper gears (11-18) here she comes !! Vibration is there. Soon as the grade eats up the top gears and im in 10th or below, its gone.
Also, i pull a 5 axle, 3 on the ground out back with 2 lift/ steer axxles in front. Turning a sharp corner / U turn (on my dedicated route ive got one, returning to off load /dump) with 140,000+ on board, "SNAP" goes the drive axle area. 4X at the spring shop, once they replaced the pin and rubber centering bushings, on one drive, but found nothing more (think i need to get to another spring shop). Im wondering if whatever is moving is throwing out the pitch on my drive shaft, seeing as it comes and (rarely) goes away.
What do you think about that ?
Appreciate your time and input.

 

I would look at getting a new vibration dampener . Regardless it's time to replace it anyway. Also I would look at replacing your rear engine mounts if they are original too. Those can give you same symptoms your describing also.