That alternating harmonic of the drivetrain

Diffs, axles, lockers, transmissions, portals, that kind of thing.
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audiocontr
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That alternating harmonic of the drivetrain

Post by audiocontr » Sun Apr 07, 2019 6:02 pm

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?
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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rmel
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Re: That alternating harmonic of the drivetrain

Post by rmel » Sun Apr 07, 2019 6:37 pm

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.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

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audiocontr
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Re: That alternating harmonic of the drivetrain

Post by audiocontr » Sun Apr 07, 2019 6:52 pm

Thanks Ron. Happens w my haffie too. Always was curious
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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4x4Pinz
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Re: That alternating harmonic of the drivetrain

Post by 4x4Pinz » Tue Apr 09, 2019 9:25 pm

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.

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audiocontr
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Re: That alternating harmonic of the drivetrain

Post by audiocontr » Wed Apr 10, 2019 7:58 am

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?
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

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4x4Pinz
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Re: That alternating harmonic of the drivetrain

Post by 4x4Pinz » Wed Apr 10, 2019 10:06 pm

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.

undysworld
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Re: That alternating harmonic of the drivetrain

Post by undysworld » Thu Apr 11, 2019 7:30 am

This thread deals with balancing the driveshaft:
http://real4x4forums.com/PinzgauerBBS/v ... nce#p61993
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rmel
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Re: That alternating harmonic of the drivetrain

Post by rmel » Thu Apr 11, 2019 7:43 pm

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.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

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audiocontr
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Re: That alternating harmonic of the drivetrain

Post by audiocontr » Fri Apr 12, 2019 6:29 pm

"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
1973 712m
(2) 1968 Haflingers 1 For Sale
1978 GMC Palm Beach
2001 F250 Diesel and trailer

ChickenPinz
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Re: That alternating harmonic of the drivetrain

Post by ChickenPinz » Sat Jan 16, 2021 4:48 pm

<since this thread seems similar>

I'm experiencing this in my 710K. At highway speed (62MPH), there is a vibration that comes in and out about every 1.5-2 seconds. I can feel it in my feet more than I can hear it, but I did try to make a recording with a Pixel 2 phone and look at the spectrogram. That puts it at about 135-140Hz. I'd share the recording, but it's just too much in the background to pick out cleanly.

The vibration might have gone away when I powered the front axle, but gear noise increases enough then it was hard to tell for certain, and I don't care for extended driving on hard surfaces with front & rear engaged.

I'm suspecting this harmonic is the result of slight speed differences between front and rear driveshafts, but that's just a guess. Perhaps if one started to mix-and-match tires that would be a test.

Do others experience this, and do we think it's cosmetic or a concern?

My next step is to capture the data with an accelerometer so I can better collect low-frequency data.
spectro.JPG
spectro.JPG (247.61 KiB) Viewed 548 times
710K

Joeri
Belgium
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Re: That alternating harmonic of the drivetrain

Post by Joeri » Sun Jan 17, 2021 3:57 am

I think it just part of the pinzgauer......there are to many rotating parts , it starts with the engine , gearbox, short driveshaft , hi/ lo case , front and rear driveshaft ( and these are in a housing that acts like a resonatingbox ) front and rear diff that has a double ring and pingion , 4 driveshafts from the axle to the portal hubs, and last the portal reduction in the wheels.....i think its quit normal there will be some noise when driving the thing. And May i ad that my 2 volvo' s ( 1 c303 and 1 tgb1111 ) where less noisy du to the way they are build....with the pinz your drivetrain IS your chassis and the body sits on top of that.....the volvo is more classic build meaning you have a frame where the drivetrain sits in.....leafsrings that hold the axles and the body on top...and all these parts have some kind of rubber mountinghardware between them......becouse the way the pinz is build you have way less rubber or vibrating free parts in there its all alu/ steel conected that lets noise and vibations run thru it :oops:

ChickenPinz
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Re: That alternating harmonic of the drivetrain

Post by ChickenPinz » Sun Jan 17, 2021 10:36 am

Thanks, J. I think what you said is well-understood by most Pinz Peeps. A simple drive at highway speed illustrates the amount of gear noise and how it couples into the body.

My question isn't about that.

My question is about an oscillating harmonic, and trying to understand if they all exhibit this behavior, or if it's indicative of some required repair to head off a failure.
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Joeri
Belgium
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Re: That alternating harmonic of the drivetrain

Post by Joeri » Sun Jan 17, 2021 12:15 pm

Well i drive a 716k and have a completely new rebuild draivetrain....new bearings front / rear diff, new bearings in the witchhats , new rebuild hi- lo case , new bearings in the portals ....and at 80 km/ h it still makes this noise....from the start to lets say 110 km/ h it makes this whyning sound but around the 75- 80 mark there are some light vibrations....if i go faster they are gone. Mine is almoust quiet when driving between 60 and 70 km/ h .....i had the chance to drive along the 712 from SGB and its the same. The pinz that had almoust no sound when driving was my 78 710m....a k will always have more noise :wink:

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