Odd vibration at 70mph+

Now that I have my catastropic failure addressed, another thing I noticed on my recent trip is that at about 70mph, I start getting a vibration, it's a very slow one compared to speed. Kind of a whump
every second or two, on and off. Doesn't go away completely in between but kind of winds up more every other second or so. It's not a horrible truck is gonna fall apart one, but it was enough to keep me below 70. Last time I did any highway driving over 70 was a few months ago and definitely didn't have it then. Truck is an 89 K3500 454 th400.
Thanks in advance, Ed
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Sounds like maybe a steel belt shifted in a tire.
Brian
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At 70mph, a shifted steel belt in the tire is going to show up as more than vibrating every second or two. Can you hear or feel which part of the vehicle it seems to be coming from?
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wrote:

Remove driveshaft and have it balanced if ujoints check out okay. The reason it cycles is that he is getting a harmonic vibration and it sound like it is starting in driveshaft. ----------------- TheSnoMan.com
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Perhaps if the u joints are okay he could put a worm clamp on the shaft and try moving it around to see what happens before he goes to the aggrevation and expense of pulling the shaft and sending it out.
Or perhaps he should check his motor and transmission mounts first.
But hell, I'm sorry what do I know? I'm just a troll.
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Well you are a troll sometimes by some of your very actions but your idea has some merit but experiance has taught me the GM driveshafts are rarely balanced well from factory and as they age, flex and rust they tend to go out of balance even more and make their imbalance known if way such as this. One way to give more insite as to whether it is a balance problem is to place vehicle in neutral at that speed and if it is a balance issue it will not change it much at all. It is does change a lot it may be ujoints. If it was motor mounts it would show itself at speeds other than this and be of different nature. ----------------- TheSnoMan.com
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Per SnoMan:

Which begs a question that's been in the back of my mind for awhile: will it damage a GM automatic transmission (4L60) to put it in neutral while the vehicle is moving.
Might sound like an inane question, but I'm pretty sure that somewhere I read an instruction manual that cautioned against putting the transmission in question into neutral while the vehicle was under way.
--
PeteCresswell

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wrote:

There is no such thing as a inane or stupid question. No it will not hurt it at all. The reason for the caution in manual is so that someone trying for neutral does not go past it and into reverse. There was a time in the old GM days that R was below L so you had to be really carefull downshifting. ----------------- TheSnoMan.com
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Yeah Roy you aren't diagnosing anything correctly if you aren't jumping in there and throwing someone elses money away. To hell with questions or basic diagnostics! Spend money first!
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On Sun, 18 Mar 2007 12:11:29 -0500, Heatwave

You mean the H with logic right? Nothing I said was bad advise here but you would have the original poster chasing his tail if it was up to you. ----------------- TheSnoMan.com
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wrote:

I recall one of your more memorable response's for a 45 dollar item was for the person to trade the truck. Sorta pkb don't ya think.
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Now you are acting like a Troll again! You just cannot seem to shake it. BTW, I have personally had to have the driveshaft balanced on 6 of my own 4x4 over the years. $ of them where GM's and one of those 4 was on a then new 89 4x4 Suburban that had a simular mild rumble at cruising speed. Dealer said it was "normal" for warranty concerns so I pull driveshaft myself and at my expense had it checked for balancing and it was out of balance and rumble it did go away when it was properly balanced as did problem I was having in other 4x4's.I have a drive shaft on a Jeep Cherokee that need balancing when I get a change to pull it and get it done. ----------------- TheSnoMan.com
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wrote:

No just pointing out that most of the time your response is bs. A little dianose's might be nice befor the op start's ripping his truck apart.
<You just cannot seem to shake

So what does it matter how many shafts you have had balanced? I've had 4X4's for 30 years and not had one balanced. Hi performance cars are another story. But it doesn't matter. A bit more info from the op is needed.

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Oh yeah this thread http://tinyurl.com/22js32 (sbj: 1999 Ram 1500...lots of problems!!)
Another snoball gem...
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wrote:

Yup, that's the one. Us troll's that don't know shit sure seem to catch the Idiots bs every time he post's it.
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You might put your truck up on a lift and run it in gear and see if it is possible to observe where it is vibrating. I did that when I thought I had a bad driveshaft, turned out to be a wheel out of balance.

than
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Ok guys finally drove on the highway again to try and get some more answers, this is what I found. The vibration feels like it starts at my feet and comes up from there through the seat as it gets worse every couple seconds. If I drop it in neutral it seems to go away at speed. I tried reproducing in 1st and 2nd gear at the same and higher rpms and could not. Should I start checking the u-joints? I don't mind replacing them if they need to go, just want to check them first if possible. Also, my truck has the center bearing on the shaft to the rear wheels since it's an ex cab, is there an easy way to check that? I've heard many different ways to check the u-joints so I would be interested to hear what you guys have to say on the best way to do so.
Thanks again, Ed

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Do you feel the vibration under your feet? Under your ass? In your hands? Do you feel it only at 70+ mph? Have you tried to duplicate in different gears? Trying to determine if it is rpm sensitive or just MPH sensitive.
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