Hello. 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? Did a test by opening the hood, putting the vehicle into drive, putting a foot on the gas and a foot on the brake, giving it gas, and watching the engine dip on the driver side. Then I repeated this in reverse, and it dips on the passenger side. Don't know if that's normal. 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.

 

*bump*

 

I may be wrong, but I think you are looking for the problem at the front when it's cause may be something at the back end.

 

I don't see how it could be rear end related. Everything I'm feeling is very prominent up front.

 

Hey Big D, I have a 2003 Ford Explorer XLT. I am having the same problem. I've changed everything in the front except the wheel bearings( because all the mechanics said the are fine). I've changed the Upper control Arms, New Inner and outer tie rods, Both axles and sway bar with new links. I've changed both rotors and brake pads, new tiers, Alignment and tire balance and rotation.

I also thought it might be the motor mount but mechanic said it's fine.

I still have that knocking noise in the front end and when I'm on the highway driving over 60 the car starts to shake (Vibrate). On rough road I hear this stupid knocking like if something is loose. But When I go underneath the car I shake and hammer everything and everything seems fine. Three Damn mechanics and nobody knows where the sound is coming from.

If I find the problem and get it fixed, I'll let you know. Please if you can do the same.

Thanks