Fed up with vibration issue

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Lowburb93

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Hi all. Ive been having an issue with my 93 suburban. Keep in mind it did this before it was dropped (spindles, springs, flipkit) Around 70 mph the truck has a vibration. Ive ruled out the following: new tires all balanced (twice actually) new front wheel bearings and rotors. New rear drums. Checked pinion angle (about 1.5 degree pinion nose down from the trans). Its been aligned since the drop. I can put it in neutral and it still does it. Ive also rotated the tires with no noticeable difference in vibration. Also ive jacked up the rear by the axle and spun it up to 70 and the vibration seems to persist. U joints seem fine. It shakes the steering wheel (can really feel it if you have both hands in it) but you can also see the pass seat wiggle. This is really frustrating especially on long hauls. Any help is greatly appreciated from a newbie.
 

Curt

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Try having your wheels road force balanced, not just spin balanced. Make sure your wheels (and it might sound crazy but...) and tires aren't out-of-round (a road force balance will tell you if your tires are out of round). Hopefully this will fix your issue.
 

jdla140

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Are you 100% Sure it shakes while jacked up? My sierra denali does this and replacing the idler arm / bracket helped IMMENSELY. The pitman arm is also super ****** out but I don't want to replace it yet. If you doubt its either of these try balance beads in the tires. Cheap and extremely effective.
 

Lowburb93

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Are you 100% Sure it shakes while jacked up? My sierra denali does this and replacing the idler arm / bracket helped IMMENSELY. The pitman arm is also super ****** out but I don't want to replace it yet. If you doubt its either of these try balance beads in the tires. Cheap and extremely effective.
Thanks, this is the answer i was hoping for. Yes it does shake jacked up but that could be more because there's no weight on the tires? I planned on slowly rebuilding the entire front end starting with the idler arm and bracket. Was yours totally fine up untill about 60 65?
 

jdla140

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Thanks, this is the answer i was hoping for. Yes it does shake jacked up but that could be more because there's no weight on the tires? I planned on slowly rebuilding the entire front end starting with the idler arm and bracket. Was yours totally fine up untill about 60 65?

That's how it started, it was fine till 60. It progressed to the point I could feel the wheel walking back and forth at 35 and it shook like a dog ******** broken glass above 50. 65+ was absolutely out of the question.
 

Lowburb93

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UPDATE: replaced idler arm and bracket with moog replacements and noticed the trans mount bolt was finger tight. Tighted everything up and the problem persisted vibration at 70 75 then it smooths out at 80 to 85
 

joep88cheyenne

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Might want to check engine mounts unless you know they have been replaced. Transount bolt loose may have affected the engine mounts. Just out of the boxing here.
 

Bob L

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I have found over the years that tire balance vibration usually appears around 35 mph and goes away at higher speeds. High speed vibration is usually drive line related. I would remove the driveshaft and look real seriously at ujoints. also make sure the rear ujoint is perfectly centered in the yoke. I don't pretend to be an expert but have been driving old cars and trucks for 50 years.
 

ed455

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I chased the same thing in a 64 F100 I lowered with axle flips (both). I even bought new wheels and tires. Couldn't get rid of it. My pinion angle was fine. BUT . . . my pinion angle and my tailshaft angle were mismatched. If your pinion angle is down 1.5° the your tailshaft needs to be UP 1.5°.

My pinion angle was a full degree off from the tailshaft angle. I made a 1/4" shim and put it under my transmission mount and that put it at the correct angle. Vibration gone - completely.

I just started chasing a high speed vibration in my unmolested c3500. Going through the same steps, so I feel your pain. I know I have wheel issues though, so I'm at the beginning of the process. Good luck, but I suspect driveline angle issues on yours.
 
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