So I had a cracked hub lock and for a long while now my truck makes this thud thud thud thud when its in 4x4 and also I can feel the thud. When the hubs are locked and 4x4 is not engaged I feel some resistance and the ride is not smooth. I bought new Warren premium hubs thinking it was a hub problem and no change. So I jacked the front end up and spun the wheels locked and unlocked with the truck in 2 wheel drive the front driveline spins when locked with truck in neutral but no thud. Anyone have any thoughts?

 

Transfer case chain? Just shooting in the dark. I was thinking front U's but is your front driveshaft tight if you tug on it? with hubs locked though your front driveshaft will be turning even in 2wd so it's only thudding in 4x4 mode which points to transfer case maybe. With truck off the ground and everything locked into 4x4 a chain will show slack by rotating front driveshaft back and forth and noticing how long it takes for the rear driveshaft to turn. Sort of like turning a harmonic balancer back and forth and watching the distributor rotor in an old gasser to check for timing chain slop. Again, just tossing things out there. Don't replace the chain or tear it apart off of this. Someone on here will know.

 

Ok thank you Ben

 

When you jacked the front end up, was the weight of the vehicle still on the suspension?

On my last truck I had a front drive shaft u-joint just touching a part of the frame. This was due to the lift. I ended up supporting the truck on jack stands positioned under each front wheel (under the shock mounts) so that the vehicle's suspension was loaded. After some driveshaft twisting and turning, I found the knock source.

This sounds like an opportunity to spend some quality time under your truck.....

Lou Braun

 

Good idea I will load the suspention next.
Would I still have the knock with hubs locked and in 2 wheel drive? Cause it goes away out of 4x4 with hubs locked

 

The above is something I didn't even think of. Good idea! If it's driveshaft then yes, hubs locked not in 4x4 driveshaft will still turn because hubs lock wheel to axle, axle turns ring and pinion, ring and pinion turn driveshaft. In 4x4 the difference is transfer case is engaged, so engine turns tranny, tranny turns front driveshaft via a double or tripple roller chain which turns ring and pinion which turns front axle which turns hub which turns wheel. Condensed.

 

So your thinking its in the t-case?

 

Just a possibility. I had an old YJ wrangler than had a stretched T-Case chain and made some noise when 4x4 was engaged. It slaps around there. But if you set the truck on jackstands with the front loaded like he said you should be able to start narrowing it down. But only in 4x4, not in 2wd with hubs locked, seems like a T-Case problem. Most likely chain. Like I said, I'm no professional mechanic though. Have you used 4 low a lot to tug on things? Do you use 4 high a lot at speeds (50+ MPH)? Just giving you thoughts. Bounce it off some others to see if they think it's a possibility.

 

I would put all the u-joints under the microscope. You may one thats dryed up and binding but not loose yet. The t-cases in these trucks are pretty stout. You do a lot of hard off road miles?

 

I'm not easy on it but I don't abuse it. The 4x4 does not get worked out allot.

 

U joints should be checked, axle shafts are easy to pull on these trucks,
I cranked the wheel at stop and could turn the axle shaft so I thought it wasnt frozen, well when I did the ball joints and pulled the shaft out It wouldnt even turn in one of the rotational directions completely frozen, was a big turd to get that one out too, just cut it with a grinder and press from there

this was on my 2000 7.3l f250

 

U joints are most probable I agree, however if it's the U joints it would do it anytime hubs were locked in manual right? Not just in 4x4 with hubs locked because anytime the hubs are locked the u joints are turning no matter what you're telling the transfer case to do. It's only when he puts it in 4x4. But maybe it's a U joint only under load, not free spinning. That would explain it. I had a buddy that went through a transfer case, a carrier bearing, and a front driveshaft in his chipped Harley F-250. He loved showing people he could chirp all 35" inch tires from a dead stop in 4 hi by holding the brake and spooling the turbo. He was running just sub 14 second quarter mile times in this thing. However, very hard on the parts. That's why I was asking about driving habits. It is possible to destroy heavy duty parts on these things.

 

Subscribed.

Got a similar problem going on. I found a passenger side wheel bearing bad but it made no change to my noise, vibration or what ever is going on.

 

Thanks for the input guys! Ill report back when I get time to check the u joints.

 

good points benny,also I was thinking rather than the axle shafts, maybe its the u joints in the front driveshaft.

I actually had a output bearing go bad behind my xfer case front yoke on my old f450 only had 70k miles on it, but it was also a 20 year old truck, just possibilities... possibilities

Dukie let us know if you find anything, had a day fun of adventure myself rebuilding the front end on my truck today haha never get tired of the simplicity of these superduty front ends (atleast the ones with leaf spring front ends)