Hi all ! This vibration my truck has is getting outta hand. I have a 2002 Superduty extended cab with a six inch DR lift all spring, 18in Eagle rims with Toyo 37in All Terrain Tires, 3.73 rear and V-10. I started getting a vibration in August after I took the truck to the sand dunes. Nothing crazy just on the way home.
I had the tires rebalanced a few months ago and it seemed to help at that time. But recently my mileage has going down from 11 mpg to 9.5 mpg. It feels as if there is some kind of drag in the drivetrain bringing down my fuel mileage. I have changed the fuel filter in summer. The vibation is in the seat and can be felt on acceleration from 45-55 then again consitiantly from 65 mph and up. If I let off the gas it mostly goes away. I have some kind of sqeaking noise that I can here faintly from the rear area of the truck on acceleration. I heard that the rear diff will move slightly during accel/decel and if that is true it makes me think that it could be something in that area or the u-joint back there. I checked the u-joint and it seems that it is tight although there is a rubber seal that is split.
Hopefully someone has had a similar situation because there really isnt anyone I trust around here to take my truck to. I dont want to replace one thing at a time. Is it possible to smoke a rear diff or chip a tooth on the ring and pinion gears? I was thinking that with my bigger tires, I might have strained the rear end to hard at one time causing a problem. I take my truck to the local penzoil place to get the oil change because I dont have a good place to work on my truck myself. I was thinking maybe they added some fluid without the ford friction modifier that I heard was important. Any suggestions would be great. Thanks !

Mike

 

it seems like your rear diff fuid needs to be changed and the limited slip additive also put in
without the additive the diff will chatter and vibrate

 

i diddnt see you had a lift and tires in the begining 37 inch tires are very tall and 3.73 gears are not enough to handle them. to much wear and tear on the drivetrain. i would do a gear swap to at least 4.10 but i would reccommend 4.56 with that tall of tire, and you will get back the lost performance it is possible you smoked your diff brcause it is hard to spin those tires but a gear swap is not cheap or easy because you also have to change the fronts to match

 

I would also check for spring wrap of the axle. With lift kits its easy for the axle to get out of alignment. Take it to a spring and axle joint and they can check the driveshaft angles to make sure they are correct. This would give a vibration with a load and cause the mileage to drop because of the bind. Let us know how it works out.

 

Might be the first thing you looked at, but are you sure the lock out hubs both are fully dissengaged? Also, is your transfer case in 2 wheel drive instead of 4x4 and the front axle is indeed not turning. I had a vibration that was driving me nuts,and I just was in 4x4 and didn't know it.....

 

If you have a vibration on acceleration with a loss of fuel mileage I would suspect a coil is going bad and what you feel is a misfire. It could also be a bad u-joint, although they don't usually affect fuel mileage. A split seal will allow grease to escape and moisture to enter the joint. The best way to check for a bad u-joint is to remove the drive shaft and flex each joint by hand. Even if it feels good, replace the joint with the split seal. It will only give you problems farther down the road. Mark the shaft and the flanges before you remove the drive shaft so you can reinstall it in the same orentation.

 

Did you shim your carrier bearing. Mine had a vibration when you start off, had to shim the carrier bearing because of the 6" fabtech lift.

 

I don't believe he will have a carrier bearing since the truck is an extended cab and not the crew cab.

 

What?

Yes he does.

I'd make sure to shim 1-1/4 to 1-1/2 inch. See what happens.

Peace

 

kingz489,
Do you have a carrier bearing? I thought only the crew cabs had a two-piece driveshaft.

 

If extended cab <B>short bed</B>, it won't have a carrier bearing. Now a long bed, I'm pretty sure it does.

 

Thanks all for the replies! I took it in at the local stealership. They had it from 8am am until 2 pm. They test drove it, fixed it, then called me to say it was ready. They didnt call me to tell me what was wrong nor the price. The service manager told me it was a bad rear u-joint and that they had replaced it. Out the door including labor, parts, and tax it was $53.00. Not bad ahey! Vibration is gone. I feel real lucky now.

 

Also I am going to replace the rear gears very soon, looking at 4.56's anyone recommend where to buy them ?