Hello. This is my first posting on these forums. I'm hoping to get some light shed on a problem I've had since i bought this vehicle 3 months ago from a private seller. I have a 1999 Explorer XLT with a 4.0L SOHC in it. Since the beginning, I've had this annoying resonance/vibration as soon as I hit 70 on the highway. It almost feels like I'm driving over very small rumble strips. Nothing close to the severity of a rumble strip. But that's the only way I can really describe the feeling. The faster I go past 70, the more it is felt. To the point of even vibrating my rear view mirror. I also feel a slight knocking under my feet, as well as vibration in the floor boards and seat. And this vibration, to a lesser degree on side roads, is most noticeably seen when there are cups and bottles in the cup holders. You can see the liquid sloshing and vibrating. Also, when coming to a stop from 30 mph under, it feels like I'm going over rumble strips until I stop completely. And sometimes when I'm driving on back roads, I will get a sudden instance of the rumble strip feeling out of the blue. So here are the things I've replaced in an effort to try to fix this problem.

complete replacement of brakes and rotors (front and back)
-I thought the rotors might've been warped and making the vehicle shake on the highway

new u-joints on the front and rear drive shafts
-Advice from other people on other forums

transmission fluid and filter replacement w/ Lubegard additive
-Figured it might relieve what I believed to be TC shudder and possible shifting issue. I thought that when I'm coming to a stop, and it's shuddering, that it might've been TC shudder. But I've shifted into neutral before coming to a stop, and it's still doing it.

new shocks front and back including axle damper shock
-Suggestion of a mechanic friend of my girlfriend

new tires
-Had the ones that were on when I bought the vehicle balanced as soon as I noticed the shaking on the highway. Didn't fix it. So I read on other forums about road force balancing. Found a place by me that did it. Told me that the tires on there had flat spots from sitting and they couldn't perform the balance. So I bought new tires. Re-balanced TWICE. Still shaking on highway.

new sway bar links
-cheap fix so I figured I'd give it a shot

new inner and outer tie rods both sides plus an alignment
-outers were a bit loose

I've done everything from rotating the front tires to the back, vice versa. I've checked everything in the front end that I could for play (ball joints, wheel bearings, upper control arm). Thinking maybe a possible motor mount issue? Don't really see a good way to test out the motor mounts. Tranny mount seemed fine. I put a long screw driver underneath it and pryed up against the cross member. Didn't really budge. I will say, though, that I'm kind of leaning towards a possible hub replacement. After a short drive this evening, I decided to pop off the center caps on my wheels and feel every wheel in the center, where the bearings are located, for how hot they were. All the wheels, except for the front drivers side wheel, were much cooler. So maybe I need a new hub. That's everything I have replaced up to this point, in a 3 month span. I'm unemployed at this time, and I can't keep blindly pumping money into this vehicle. I thought I stumbled upon a rare gem of an Explorer, because the thing is in great physical condition. Who knew that this underlying problem existed. Any help you guys can give me is greatly appreciated. Thanks for reading.

 

Have you checked the front drive shaft - from the transfer case to the front end? Also, is the four wheel drive engaged and you have not noticed it is? Maybe high speeds with four wheel drive engaged is the cause of vibration?

 

The front drive shaft is a replacement one from the junkyard. The CV joint side looked good. Boot isn't cracked and wasn't binding when you moved the drive shaft around the cup. And I immediately put a new u-joint on the other end just to be safe. As for the 4WD being engaged, as far as I can tell, there's no sign of it being on inside the vehicle. The switch is on auto. There's no light on in the instrument cluster saying that it's engaged. The 4WD works just by using it on dirt roads. Doesn't feel like it's on during normal driving. Is there a fuse I can pull that controls the 4WD?

 

I did a bit of Google research and found the following post. There are a few different approaches to disengaging 4wd here. If you don't find your answer at this link, the internet is a powerful research tool.

http://truckexplorer.org/ford-explor...ged-93340.html

 

Duplicate of previous response and I don't know why!!!!!!

I did a bit of Google research and found the following post. There are a few different approaches to disengaging 4wd here. I you don't find your answer at this link, the internet is a powerful research tool.

http://truckexplorer.org/ford-explor...ged-93340.html

 

I've removed the front drive shaft before, to eliminate any symptoms that a bad front drive shaft might cause. That automatically disables 4WD. Still had the symptoms I'm getting on the highway.