Drive Train Harmonic

[buckeyeduffer]

During this trip (odometer @ 6654 total miles) we have noted an "harmonic" (rrr - rrr - rrr - rrr) noise from the coach (we assume coming from the the drive train) when operating at 63-66 MPH, and more noticably when pulling a grade. Have checked tire pressures and lubricants and they are OK.

Anyone else having the same? Feedback will be appreciated.

[ernieh]

I have noted a similar sound on my 03 Journey. I always felt that it was exactly what you described, a "harmonic", similar to a twin engine airplane with the props slightly out of sync.

I don't think it's anything harmful, just two "somethings" on the engine/drivetrain turning at a slightly different rpm. I think that the sound is there all the time. It just gets transmitted to the chassis when the load on the drivetrain is increased.

[EngineerMike]

If its getting worse, time to check U-joints. Lotsa folks have trouble early in coach life w/OEM improperly lubed u-joints.

[powerboatr]

Quote:

Originally Posted by EngineerMike If its getting worse, time to check U-joints. Lotsa folks have trouble early in coach life w/OEM improperly lubed u-joints.

I agree as well, i have found a few zerks that were dry.
i would also check the torque on all the wheels, i had two up front that were loose enough i turned em pretty easy with just a short ratchet,
and the bug hub cover out back, loosen its attachment nut then recenter the cover and tighten the hold down nut.

[buckeyeduffer]

Thanks Guys:

Scheduled for a service tommorrow at Freight Liner so will be sure to check all-the-above.

Spent this morning under the coach reinstalling the step-control assembly. The main pivot bold had loosened, and dropped down resulting in snapping off one of the assembly drive mount bolts when we unknowing applied weight to the step. Another opportunity for retro-engineering when I get a chance. Oh well, retirement is a bear, so nothing better/else to do I guess.

[buckeyeduffer]

Freightliner checked all systems during service and assured me that the harmonic was normal (as ernieh predicted) and probably not a problem. Only dry zerk they found was on the steering, and the tech told me that the same zerk is dry on nearly every new chassis he services. Stated he has reported it to Gaffney as a CPI issue for the company. The Kansas Truck Center service program was excellent. As a drop in I was not sure what to expect but they were great. Had problems getting a fuel filter for the Onan service but otherwise a good experience with favorable labor pricing.

[ernieh]

Just out of curiosity, which zerk was dry? Was it one of the ones on the steering column u joint? I've rarely seen anyone lube them, especially the one under the rubber boot.

[buckeyeduffer]

Not sure which one it was.