Vibrating 80 at highway speeds

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Jun 25, 2003
Rixeyville, VA
The 80 recently has seemed to develope a real bad virbration on highway speeds usually at 70+ mph. it only happens when I'm giving in light throttle, just enought to keep the speed. if i accl. alot it goes away and if i totally let off the gas it stops. any advice. it is 10yrs old and 207k miles. maybe jusy worn out diffs or something?
Can you tell if it's front or back? Do anything to it lately like rotate tires or take it wheeling?
I would say maybe from the back but not sure. kinda feels all over, also landtoy what exactly are you asking? and no i have not taken it wheeling or rotated the tires, it has done this for awhile now.
have same issue with my '94, although I have about six inches of lift. I thought it might be an issue with the transfer case viscous coupling. But have been unable to really pin point the source. For now I'm just living with it, but would love to get rid of it. I have tried removing each driveline one by one and locking the center diff to drive in two wheel drive and the vibration goes away unless both drivelines are in. Any info anyone has would be great.
tires or VC...tie rod perhaps?
When you say vibration, does the whold vehicle shake or is it a hum that you hear and feel a bit?
Are your tires the same size,brand and tread wear the same?
I guess its more of a hum i can feel very good. tires are all the same size, the stock type ltx's. rear ones are newer than the front though.
I'm having basically the same problem. Usually between 65-75 MPH on the freeway. It's pretty much a "full body shake" which you can feel thru the seats and see in the A and B-Pillars while driving. At first I thought it could be the tires, so I had them rebalanced. No effect. There was always the possibility that a tire was out of round, so I bought new tires. (Great excuse for new hoops ;)) Full post on those to follow.

Well, it's still there. Now I'm thinking driveline, wheel bearings, or maybe the VC overpacked with grease??? I've got a load of parts from C-Dan, so new brakes and full Birf service next week. Will check the wheel bearings and have at least the front drive shaft checked/balanced while it's out. If I come up with anything, I'll post it.
CH05, if the front and rear tires have a measurable amount of wear, you are putting stress on your VC in the T-case.

The hum at 70, I think you will have to live with it as I replaced all of the wear items in the drive train from the t-case back including a new t-case. The only thing I havent replaced was the rear diff bearings. I have them but havent got around to replacing them.
I was not trying to get rid of the hum, I was just replacing all the wear parts as I work on the 80.
I have had this problem several months back, while driving at speeds of around 65 to 75 mph I noticed the truck virbates. So after rotating and rebalancing the tires without any luck, Since the front two tires were the same size, they were different models and the waer on them were also different so I decided to replace all the tires with brand new ones that's matching (Dunlop Rover AT's). To my surprise the virabation went away, so I personally think that all the tires should be the same size and have equal wear and this might be a good start by changing the tires.

[quote author=landtank link=board=2;threadid=9481;start=msg83317#msg83317 date=1073015046]
Shortbus take a good close look at those bushings in the front spindles. I had a oscilating hum that has disappeared since I cleaned and greased mine.

Thanks Tank... :beer: I'll make sure to check those out. It's weird, because it doesn't always do it. Sometimes, it's more pronounced than others. For a while it seemed like I could make it go away if I would "climb" the ruts in the freeway. Out of 72 vehicles I've owned, this is the first 4WD. I think it's a little harder to diagnose these things with so much more rotating mass and parts. But since I bought this thing primarily to tow with, I'd really like to smooth it out.
I just starting experiencing this exact same problem, it seems to be the worse at exactly 70mph, > 70 seems normal and <60 feels totally normal. If I'm accelerating I can barely notice it through 70 but If I take my foot off the gas it is more prounounced around 70mph. I just got back from a trip to the sierras where I hit a snowbank at ~20mph, so I just hope I didn't damage anything there. My tires are pretty new and all have even wear , but I guess something could of gotten unbalanced, but the truck still drives straight when I take my hands off the wheel . This was also the longest trip ~800 miles I've took the truck on since I have owned it. I also was using 4wd low a little bit also if that could possible have anything to do with it.

From a quick inspection of under the car everthing looks normal except for a lot of grime on the inside of the front wheels.

I also starting getting a check engine light about half way through the trip ??? , but that's another issue...

I'll be sure to post back if I figure it out, I might have to take it in anyway to see what's the deal is w/ the check engine light.
Unfortunately I don't know. You jump a couple of pins in the service socket and count the blinks of the CE light. They are a 2 digit code and that will tell you what is going on. Search the archives, it's been mentioned regularly. I'll check and edit this post if I find something.
There should be a label on the underside of the hood that shows what pins to jump and their location in the data link connector. Same pins are used to read the codes as used in setting the base timing.

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