A strange sound and accompanying vibration

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t-bone80
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Joined: Thu Jun 04, 2009 6:12 am

A strange sound and accompanying vibration

Post by t-bone80 » Tue Jul 14, 2009 11:16 am

I have a strange sound and accompanying vibration that does not start until the truck is running at 70 km. The sound is the vibration through the body of the truck and is like vrrrrrrrrrrrrr and it is at the same time as the vibration. The vibration and sound last about 3 seconds and then no sound or vibration for maybe 1 second. This cycle repeats itself and the time line is the same as you continue to go down the road at 70km. If you speed up to 80km the vibration gets worse and you can just start to feel that the truck is trying to slow down during the vibration part of the cycle. As for the truck slowing down during the vibration part of the cycle the speedometer does not indicate that it is slowing down, it just “feels” like it.
Under 70 km the truck runs fine and has no vibration what so ever.
These speeds are as indicated by the speedometer and I have not checked the exact speed by GPS.
This is a strange request and not being in the truck when it happens makes the diagnosis next to impossible but I was hoping someone could give me a good idea of places to start looking.
Thanks in advance!

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Erik712m
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Joined: Sun Jan 21, 2007 7:52 pm
Location: Wichita, Kansas

Post by Erik712m » Tue Jul 14, 2009 11:18 am

Drive shaft needs balanced take it out and send it to Scott.

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pinztrek
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Post by pinztrek » Wed Jul 15, 2009 9:04 pm

Erik712m wrote:Drive shaft needs balanced take it out and send it to Scott.
I don't claim to be a driveline expert, but that same exact symptom can be seen with heavily lugged tires even on vehicles with balanced driveshafts.

It's essentially a beat note between the different "howls" of the tire due to differences in rolling radius, and will phase in & out over a 2-5 second period. And when it's in phase, it can resonate the pinz it's that strong. IE: You "feel" it.

On the otherhand, if you are running street tires, then it's probably not that! :-)

If I recall, there is a test you can do to isolate the driveshaft resonance. (Put it in 4wd, look for a change in the noise, or something similar) Before I went to the trouble & expense of having the driveshaft balanced I'd sure try to confirm that's the issue!

Have fun,

Alan

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ka
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Post by ka » Wed Jul 15, 2009 10:04 pm

i have that vibe a bit in mine. the test is to get the pinz up to vibration speed in 2wd and shift to 4wd. if the vibe disappears then the front drive shaft is out of balance. it was dennis's post that described that a while back.
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