Bad Vibration

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Berf

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I have a 2nd Gen 4WD V8 that started out with just a very light shudder under heavy acceleration. I went on a long trip and after several hours on the road, the vibration starting getting really bad, it makes the whole truck shake. Felt like I was driving over rumble strips any time I pressed on the gas even a little bit. If I let off the gas, go downhill, or coast it goes away and the truck is smooth again, but as soon as I press on the gas the vibration comes back, and the more I accelerate the worse the vibration becomes. I got the truck home and checked out the carrier bearing and I don't see any obvious problems, and the rubber around it looks ok. Tires are balanced and fine, it isn't a tire or wheel issue. It's got to something in the driveline, but I'm having a tough time identifying the source of the vibration since it shakes the whole truck.

I put the truck up on jacks and put it in gear at idle and I'm not seeing a problem, but it isn't under any load either, so it's a bit tough to duplicate the problem this way.

I'm wondering where I should start looking, and what is the best way to isolate the cause. Is there a common component failure that causes this that I should check out first?
 
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Check your drive line, sounds like your Steady bearing is done... as well as inspect the Ball Joints, to inspect the steady bearing look at the Rubber hanger around the drive shaft if it is Broken away you need to replace it, you can do this yourself in a hour..
But you will need a new Drive Line which you can get off Rock Auto, and some tools and a long extension bar and Torque bar, UN bolt it from the rear axle And cross member and transmission and slide it over top of the cross member and reverse the process for installation...
 
I put the truck on jacks and checked the carrier bearing assy on the drive shaft. I believe this is what you are calling the Steady bearing. It all looks good and the rubber around it is intact and doesn't look broken or torn.
 
It isn't the engine. It has all new plugs, fluids, and filters (including gas filter) and the engine runs fine and the transmission shifts fine. It is a drivetrain vibration of some kind. Truck has 150 K miles on it. It started after I ran it at 80mph on the highway for several miles. It's either a U joint, carrier bearing, or CV joint or axle issue. It only occurs under load. If I lift off the gas pedal it goes away, if I push harder on it, the vibration gets worse. Feels like driving over a rumble strip. Higher speeds make it worse.
 
I'm going to attempt to rig up a camera to the underside of the truck and go for a drive and see if I can capture on video what is going on.
 
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Shot video of carrier bearing and front right axle and CV joint, all looks ok. Pulled rear driveshaft, checked U joints, carrier bearing, and front CV joint. All feel fine. In the process of changing transfer case fluid. Previously changed trans fluid about 500 miles ago. Now I'm starting to wonder if this new LV trans fluid is causing this vibration. Haven't yet pulled front driveshaft to check it out, but that is probably next on my list.

Question: Can I remove front drive shaft and drive the truck with it removed to eliminate a problem with the front drive system?
 
I pulled both driveshafts out again, and this time I replaced all three universal joints on them, and repacked the CV joints with grease, and changed the transfer case fluid. Vibration under acceleration remains. Now I'm suspecting one of the axle CV joints may be the cause.
 
Are you checking the driveline with stands under the rear lower control arms.? That is the best way. It represents the wheels being on the ground, and no abnormal deflections.
 
Yes, but the problem is the vibration only occurs under load, so running it on stands doesn't duplicate the problem.
 
I've had a similar problem twice. You say you had the wheels balanced? That was one problem with me on another car. An inside balance fell off one of the wheels, and the shaking at about 60 mph felt like the whole front end was falling out. I took it to Goodyear, explained what was happening and they suggested re-balancing the wheels. I though they were nuts. But, they rebalanced and fixed my problem. The other time was in my F150. The drive shaft had a balance patch welded on that apparently fell off. I had the drive shaft replaced and had no more problems. Finding an issue of this type can be exasperating. Good luck with it.
 
It is NOT the wheel balance. The vibration does not occur when I lift off the gas pedal. All wheels are properly balanced. It is vibration in the drive line only when under load, like going up a hill or accelerating.
 
ReggieT said:
The other time was in my F150. The drive shaft had a balance patch welded on that apparently fell off. I had the drive shaft replaced and had no more problems. Finding an issue of this type can be exasperating. Good luck with it.
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I had that problem with a 1st gen ST. Had to replace the rear driveshaft, and the vibration went away. Maybe the cruise at 80mph threw a driveshaft balancing weight? Not that cruising at 80 should cause that, but something more to check.
 
you seemed to have covered most things i could have thought of, but maybe a engine mount, when under load it could create a balance issue that would travel threw out truck, when under load the engine likes to try and twist so it could look ok but put some pressure from jack underneath to see or maybe trans mount, only few things ya did not try..good luck and keep us posted.
 
Looks like I'm headed for a transfer case rebuild. Can hear noises in transfer case and see metal in transfer case fluid after draining it. Came out really dark after less than 100 miles on new fluid.

Anybody wanna buy a used Sport Trac?
 
Berf said:
Looks like I'm headed for a transfer case rebuild. Can hear noises in transfer case and see metal in transfer case fluid after draining it. Came out really dark after less than 100 miles on new fluid.

Anybody wanna buy a used Sport Trac?
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You aren't serious about selling it. A rebuild is not that bad or a used one. That trac has alot of good years and miles left in it.
 

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