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That alternating harmonic of the drivetrain

Posted: Sun Apr 07, 2019 6:02 pm
by audiocontr
I've heard it in many vehicles, but was always curious of its origin as I noticed it in my pinz today, in its 2019 maiden voyage.

It's a drivetrain harmonic that winds up and down at higher speeds... maybe at about 60 hz... the pitch goes upppp and downnnnn and upppppp and downnnnnn. The faster you go the more pronounced.

Is it a drive shaft out of balance? Get it rotating fast enough and will delve into harmonics?

A tire issue?

The thing that gets me is the constant cycling. Move at a constant 60 mph and you can hear it go up and down at a constant pace. Same frequency.

Any ideas? Have you had similar?

Re: That alternating harmonic of the drivetrain

Posted: Sun Apr 07, 2019 6:37 pm
by rmel
A shaft out of balance would just get progressively worse with speed.

The gremlin you may be experiencing is the front diff, tracking from
left to right, there's some play in there. I have a cyclical noise/vibration
which is noticeable at about 45mph, and continues up to 60mph. After
63mph or so it is significantly less noticeable -- as if the slop in
the diff planetary gears are hovering in neutral territory.

Try running up just over 60 and see if there's any change. Ya, your
RPM are gonna be on the high side.

Re: That alternating harmonic of the drivetrain

Posted: Sun Apr 07, 2019 6:52 pm
by audiocontr
Thanks Ron. Happens w my haffie too. Always was curious

Re: That alternating harmonic of the drivetrain

Posted: Tue Apr 09, 2019 9:25 pm
by 4x4Pinz
from what I have seen it is a combination of a couple things. The driveshaft was not balanced as well as you would think, in most cases just a piece of metal welded at a point determined by a rough balancing system. the compounding issue is the carrier bearings getting a little sloppy form wear. the combination will cause the harmonic issue. Of course you can hit a speed that will put enough force on them to make them quitter. The speed will eventually need to be increased to make up for the increased wear and at some point you will not be able to out run the harmonic issue. This is why the simple test is to engage the transfer case, which helps lock up the carrier bearings, and the noise should subside. Just another sign of the pinz getting older. I have a 712 that is much like some of the 710's when it comes to the noise. Lots of mileage and use. It is going to be time to remove, balance and replace my carrier bearing in the witches hats and rebalance the driveshaft.

Re: That alternating harmonic of the drivetrain

Posted: Wed Apr 10, 2019 7:58 am
by audiocontr
Take me a bit further into the life of the carrier bearings.... If the harmonic is the slight worn, what happens in another 10k miles?

Re: That alternating harmonic of the drivetrain

Posted: Wed Apr 10, 2019 10:06 pm
by 4x4Pinz
well I am down the well worn road. To date I have no known ill effects but I am sure it is causing faster wear on other parts of the differential and transfer case. Replacing them is on my VERY short list of things to do. I had the work done on my 710 and I would venture that over 80% of the issue went away by just balancing the drive shaft. I know I should have replaced the carrier bearings but was not driving my 710 that much at the time.

Re: That alternating harmonic of the drivetrain

Posted: Thu Apr 11, 2019 7:30 am
by undysworld
This thread deals with balancing the driveshaft:
http://real4x4forums.com/PinzgauerBBS/v ... nce#p61993

Re: That alternating harmonic of the drivetrain

Posted: Thu Apr 11, 2019 7:43 pm
by rmel
Between 40mph to 60mph, the front driveshaft rotates at 45 to 68 Hertz -- cycles/sec.
Hmmm, that's like a power hum. But an unbalanced shaft will worsen with higher rpm
does it? Or, as pointed out before, the centering bearings may be a culprit here, which
with higher rpm "self-center" and stop the vibration. The other issue would be the front
Diff, a harmonic -- repeating vibration measures over 5 to 10 seconds and tends to be
a function of the road surface -- that one is play in the planetary gears and higher road
speed does suppress this. I have often wondered if a EX-II upgrade would improve on this.

Re: That alternating harmonic of the drivetrain

Posted: Fri Apr 12, 2019 6:29 pm
by audiocontr
"The other issue would be the front
Diff, a harmonic -- repeating vibration measures over 5 to 10 seconds and tends to be
a function of the road surface -- that one is play in the planetary gears and higher road
speed does suppress this."

This is what im experiencing