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Old 11-11-2018, 10:46 PM   #1
Mini-Skoolie
 
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Harmonic vibration noise? Urgent!!!!

Looking at picking up a bus this weekend.
2001 30ft flat nose dt466E with mt643 amtran.
The odometer doesn’t work. They reprogrammed the govenor to 71 mph .
Tires are excellent and no rust. Has about 230,000 miles on it according to them reading it off the ecm. Besides that I think I finally found myself a bus. From this time last year I bought a van after looking at shuttle buses and have been entertaining the idea of a bus . Sooo
They also say when under 35 mph and heavily accelerating there’s a bit of a harmonic vibration noise??? But then it goes away? No too sure what they meant. I asked if it was an aero dynamic thing or something . Any suggestions before I open up and spend money on davey jones locker?
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Old 11-11-2018, 11:02 PM   #2
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It may be a bad U joint. Possibly drive shafts out of phase. Check center bearings too. It really depends on how the oscillations feel. If it feels 4-5 times tire rotation, Drive line. If it goes with tire rotation, may be tires, rear bearings or suspension shift.
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Old 11-12-2018, 07:07 AM   #3
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Quote:
Originally Posted by bluebird90 View Post
It may be a bad U joint. Possibly drive shafts out of phase. Check center bearings too. It really depends on how the oscillations feel. If it feels 4-5 times tire rotation, Drive line. If it goes with tire rotation, may be tires, rear bearings or suspension shift.
By tires do you mean wheel bearings? The tires look good.
How could I check u joint and center bearings ? What should I try to feel for in the oscillation ? Just that it’s turning in sync? And by suspension shift what exactly does that mean? Like the leaf springs move? I’ve never really learned to much about drive train and other components like this before?
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Old 11-12-2018, 08:22 AM   #4
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Tires are excellent...
What is the date code - on all tires? Tire "appearance" means nothing.

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They also say...
Have you not driven it yourself? If not, that would be priority one for me.

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By tires do you mean wheel bearings?
No, tires. Tires can be out of round, out of balance, etc. So can wheels.

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The tires look good.
Again, appearance means nothing. Check the date codes, put a glove on and run your hand around the tread of all tires. Do some Googling to see what the results should be. Tires are not cheap so I'd suggest not minimizing this.

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How could I check u joint and center bearings ?
Diagnosing a vibration using text is very difficult. My suggestion is to do some Googling for the various systems and descriptions of how it feels. Sadly, without experience, it is like Reading WebMD - you end up thinking you can have every disease you read about...
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Old 11-12-2018, 08:35 AM   #5
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While you are checking things out...see if the engine itself has any kind of harmonic balancer. If so, is it functional (if fluid, a leak can cause a lot of vibration).
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Old 11-12-2018, 08:42 AM   #6
Mini-Skoolie
 
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What is the date code - on all tires? Tire "appearance" means nothing.



Have you not driven it yourself? If not, that would be priority one for me.



No, tires. Tires can be out of round, out of balance, etc. So can wheels.



Again, appearance means nothing. Check the date codes, put a glove on and run your hand around the tread of all tires. Do some Googling to see what the results should be. Tires are not cheap so I'd suggest not minimizing this.



Diagnosing a vibration using text is very difficult. My suggestion is to do some Googling for the various systems and descriptions of how it feels. Sadly, without experience, it is like Reading WebMD - you end up thinking you can have every disease you read about...


Havenít driven it myself. Itís parked kinda back in a wooded area where they live and is a little tight to get out .
Probalay drive it this weekend. Iíll look up more on the date codes for next time I go see it. They donít look dry rotted or worn unevenly like another bus I had looked at. But again yeah I get it . Yeah itís starting to feel like the more I look into it the bus might have cancer. But who know if that problem goes away past 35mph thatís seems strange. Next time Iíll get on the ground and mess around with the ujoints also
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Old 11-12-2018, 08:45 AM   #7
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While you are checking things out...see if the engine itself has any kind of harmonic balancer. If so, is it functional (if fluid, a leak can cause a lot of vibration).
Man I looked up harmonic balancer and it seems like just a pulley or something for the belt to go around. Iíll look more into it.
Only other thing I noticed was guy had dog house cover off. And engine looks good. But when shutting off towards the front driver side thereís seems to be a loose connection of an it fitting or something . Besides that it looked alright. I was just told by someone else who checked it out that the owner had mentioned this (harmonic vibration)
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Old 11-12-2018, 03:09 PM   #8
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A vibration that appears around 35 MPH and disappears at higher speeds is not unheard of - I drove a truck with a similar condition for months (and thousands of miles) with no issues. I do not remember what the cause was. It *Felt* like tires to me. Another truck had that issue at around 50-55 MPH (actually it was a hub piloted wheel and the centering tabs were broken, allowing the wheel to become off-centered).
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Old 11-12-2018, 04:05 PM   #9
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A harmonic balancer only starts making noise if the rubber dampeners in it are wore out? If so it is more of a clanging banging noise and you can see it wiggling and wobbling at any RPM. if it is making a noise?
Normally don't make a noise like it is out of harmony? It's either rattling or not? If it is then I wouldn't run the motor until it is fixed cause it will mess up the front seal if not already leaking and long term it might mess up the front crankcase bearing and journey.
Could be something else?
My bus? After it sets for awhile the tires will flat spot from setting and I can feel it up to 25-35 before it goes away but after a good drive or a couple days of driving it will go away.
Drive shaft center support bearing/mid shift bearing is a must check for grease and a good rubber around the bearing cause the rubber is the part that takes the beating if/when everything is not properly aligned or wore out.
If you feel any extra clunks or thunks when you put it into gear then I would look at u-joints and grease them if you don't feel any play in them
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Old 11-12-2018, 05:28 PM   #10
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A note on checking u-joints, block the wheels and put the trans in neutral. if there is any "load" on the driveshaft a loose u-joint will not show.

Harmonic balancer may or may not make noise however if you watch it while the engine is running it will often run out of round and wobble if bad.

I would be looking mostly at driveline and tires. Anything engine would likely happen at certain engine rpm's in each gear rather then just one highway speed.
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