I have a 1999 Super Duty 4wd with 290k. It is equipped with a dash switch for On The Fly four wheel engagement. The hubs are lock/auto hubs. When the hubs are locked and in 2wd turning all most to full lock in either direction there is a consistent thumping sensation that I feel through the steering wheel. When in Auto mode 2wd there is no thumping. The u joints have been replaced, axle seals replaced, new hubs tried and removed, drive shaft from differential to transfer case removed and inspected, and transfer case internals inspected for correctness. While the drive shaft was removed the truck was driven and no thumping occurred. Got any ideas. I am no mechanic so keep it simple!

 

Had the same thing. It was the cv ball joint on the end the front driveshaft that attaches to the transfer case. On my 08 i had to replace the entire front driveshaft.

 

I have something similar going on with my 04 fx4. I only hear/feel it when I'm moving and it increases in speed and intensity the faster I drive. I can feel it in the pedals and the steering wheel. Might crawl underneath and take a look. Would really like to make it stop.

 

Thats what mine did. Pull the front shaft and it goes away

 

You mean completely remove the front shaft? What's the issue with it? U-joints or something?

 

Yes romove it. Its the ball joint that is going bad. Its basically all one part. Unbolt it from the transfer case and the front pumpkin

 

I've been reading up on this. Apparently, the front driveshaft isn't supposed to spin in 2wd. So, if it is spinning then I may have multiple issues here. I guess I didn't specify that the noise happens in 2wd. Any thoughts?

 

Your Shift on the fly is not working. When you disconnected the drive shaft to the front it goes away correct. With Shift on the fly there's a motor on the transfer case to engage and dis-engage the transfer case, it's not working. Easy test if your can turn the front drive shaft by hand with the dash switch on 2wd than it is in 2wd if you can't than it's always in 4wd. Replace the motor on the transfer case I don't know what it's called. My experience with the auto hubs they don't work, but thankfully Ford allows you to lock the hubs manually. With 4wd engaged on dry pavement full lock in either direction (sharp turn) you will experience wheel hop, it's not designed to be driven on dry pavement.

 

Still trying to diagnose my thumping noise. The front drive shaft will rotate by hand when in 2wd and I crawl under the truck and grab a hold of it. U joints may be a bit loose. Also, there's a nub where the front left wheel mounts that is showing fresh metal like it's been making contact with something. The other thing is when I'm cruisin down the road listening to the thump, I can bump the wheel to the right and the thump goes away for a second. So basically, when I turn right it doesn't thump. Could it just be a wheel bearing issue?