I recently bought a 1998 ford explorer XL and when I start driving the car my steering wheel and dash shake a little bit and I feel/hear a knocking under the car but in the center underneath where my center console is. Could this be an issue with my drive shaft? any help would be greatly appreciated.

 

With that description it could be a lot of things. Shaking in the steering wheel and dash would make me suspect a misfire, but it also sounds like you only notice this once the vehicle is moving, not just stopped in idle. Is that correct? If so, then it could be a driveshaft, but it could also be a transfer case issue. There was at least one version of transfer case that was used for a short time, but around 1998 (I don't recall if I experienced this on a 1996 or a 1998) and it would pop and knock and cause a vibration, usually just under a light load (such as going up even small inclines/hills). We found it by using a ChassisEar to determine where the noise was loudest, then searching the Internet for "transfer case popping" and the model year. It was a co-worker's Explorer and my ChassisEar.

-Rod

 

Thanks for the reply. there is no vibration or knocking in my car when it is still. like you said my car starts knocking/vibrating under light loads such as going up small hills or when I just start increasing my speed on the road at first. Because of the fact that my car only does this when in motion does that mean I should look more into the transfer case than the drive shaft? or do you think I should get a hold of a ChassisEar? I have never heard of that tool and am wondering if it will help me find out what is causing the vibrations. Also if my car only starts presenting this problem when the car is just getting in motion on the road how would I use a ChassisEar to diagnose whats wrong if my vehicle up on a lift? Thanks again for the reply I will look into the tool while I wait for any more responses.

 

I am pretty sure the manufacturer of the ChassisEar is Steelman, but it's also been re-branded and sold under some other names as well. There are a couple of options, one wired and one wireless, but the result is the same. You place up to 7 microphones in different locations around the vehicle. For something that requires a test drive, the wireless version is typically more convenient, but also quite a bit more expensive. Then when the noise is happening an assistant can switch from microphone to microphone to determine what area seems to be the loudest. Then you can reposition the remaining microphones closer to the area of interest and keep "zooming in" until the source of the sound is located. Each microphone is mounted inside an alligator clip so they also do a pretty good job of picking up vibrations as sound.

The drive shaft could still be the source of your vibration and to determine that you obviously would not want to mount a magnet on the rotating drive shaft, but you could mount a microphone on the differential housing near where the driveshaft enters as well as on the transfer case. If the axle is the source I would expect the sound level to be similar at the differential housing and the transfer case, but less loud further away from the entry points to the axle and transfer case. If you start to narrow it down to the axle and your Explorer has 4WD versus AWD you could remove the front drive shaft to see if either of the joints bind up and if the noise goes away.

-Rod