'99 XLT vibration issue

[Big D from CT]

So I'm trying to track down and isolate a vibration issue. This vibration occurs in 2 parts. City driving vibration, and highway driving vibration.

The vibrations that are occurring during city driving aren't physically felt. The only time it's physically felt is deceleration coming to a stop. It almost feels like going over a rumble strip. Other than that, it's only noticed by my passenger seat vibrating slightly. And whenever I have a drink in the cup holders of the center console, you can see the liquid dancing around. It's a rippling effect in the liquid, not sloshing. Also, the compartment lid doesn't shut all the way and that shakes as well.

Onto the highway vibration. All of the above occur, as well as once I hit 70, there's a heaviness to the vehicle. It's really hard to explain it any other way. It also usually occurs around 2500 RPM. And once the engine is cruising at that speed/RPM range, it has a deep groan/throatiness to it. Once I accelerate, though, the groan smooths out. Say I were to accelerate past 80 and cruise at that speed, the groaning/throaty feeling returns, along with a vibration that shakes my rear view mirror. It's not a choppy, violent vibration. It's a very fine, tight feeling fast vibration, if that makes any sense.

I've already replaced the truck with new shocks, new axle damper, new brakes and rotors, new tires. All within the last month. I bought the vehicle used because it was in great shape. Unfortunately, the owner didn't live near a highway so that I could road test it at highway speeds. I'm hoping some of you guys can shed some light on this. Maybe suggest some things I should look into getting checked/ replaced. Maybe it's happened to some of you. Thanks

 

[drbenz]

One possible area is the driveshaft ujoints. I need to pull the front shaft in mine as I can feel the vibration change from accl to decel. If the joints are rather bad you may be able to just look at them (rust coming from the cap or cap out of line with the joint) and tell but most likely the shaft will have to come down for a careful look.

 

[Big D from CT]

I haven't pulled the rear one yet. But the front has a brand new u-joint.

 

[Big D from CT]

*BUMP* There has to be someone out there in forumland that has suffered these similar symptoms

 

[captaindynamo]

Did you ever find the source of the vibration? I'm experiencing the same thing. Truck runs fine, but sounds like I'm driving on gravel when I get around 70mph. Pretty sure it's coming from the front end. The vibration goes away if load up the drive line either by acceleration or turning on 4wd for a second.

 

[Big D from CT]

Haven't resolved it, yet. When I get the money, I'm going to bring it to a dealer and have them do a NVH(Noise Vibration Harshness) test.Somethings triggering that feeling immediately hitting 70. Doesn't make any sense to me. Hopefully they will find it.