ok bear with me on this as this write up will be long and drawn out...

I have an issue with the 4wd on my SD. In 2wd there is no issue. In december when we got 20 inches of snow the 1st time I locked the hubs and engaged 4wd I started hearing a CLICK in the left front assembly. I had to use 4wd to travel and could constantly hear the click click click...

It started to get more prominent but once the roads were good it was back to 2wd. Last weekend we got snow again... locked the hubs and engaged 4wd..the CLICK now was a slight clank clank... during my 9 mile ride to work the clank became a vibration.. and when turning into my work it was LOUD and shaking the truck... it sounded like a u-joint exploding... but all the while the wheel still spun in 4wd...

Leaving work that night I still had to use 4wd to travel. Under torque the entire truck would shake. Once you got cruising, the vibration would go away and all you'd hear is a clanking. If I would just burp the throttle the entire truck would shake violently... I got close to home and decided to just disengage the left hub, basically making the right front the only drive tire... NO NOISE, NO CLUNK, NO VIBRATION AT ALL!?!?!?! The truck pulled alot now but that was too be expected...

So now my mind is burning up thinking what could it be? Is it the locking hub? If that was bad it wouldn't stay engaged. It would either stick and not come out of LOCK or if it stripped you'd hear grinding and the tire wouldn't spin when torque was applied...but it still locks and spins... so now I'm thinking possible U-joint failure. The U-joint is fine. It's lubed and tight.

Earlier today I did road test with someone walking next to my truck. We locked the hubs and moved back and forth. NOTHING but I didn't have 4wd engaged yet. I put it in 4wd and click click click started in reverse. As I backed out of the driveway with the wheels turned, not only did noise start but a CLUNK CLUNK and you could actually feel the front end start to fetch and then it would CLUNK free. This was always with the wheels turned. When the tires were straight in reverse was clank clank. In drive the clank turned to clunk and vibrate. We disengaged the left hub and like last time NOTHING. No noise no clunk going straight or turning. Locked the hub again and problems came back. A shot in the dark we kept the left hub locked and disengaged the right hub... this blew my mind what happened next....

NOTHING. With the left hub locked and the right hub free the truck drove fine. The left tire was engaged with NO NOISE nor fetching. We locked the right hub back in and all the problems came back... so now we are thinking the differential...

I checked the fluid level as this would be the easiest thing first... FULL. I did not pop the cover to look at anything because gears and stuff aren't my thing, but thinking back to when I was turning out of my driveway, since the inside tire is turning at a different speed then the outside and fetching up doing so this seems to be a sign that the differential is failing? I don't know whether the truck has an open diff or a limited slip or whatever...but the idea of how a diff distributes power to each wheel at a time makes me think the diff is the problem. Like I said when you disengage a lock hub you have a free spinning hub with no resistance so the power can just go to the other side theoretically, but once both are engaged the diff can't split the difference effectively?

Basically what I'm asking is has anyone come across this before? Not just with SuperDuty's but any front diff. Does this sound like clutch packs in the diff are shot? I've had spider gears a rear diff go before and that was more of a lock up then anything. Should I replace the gear oil and add a tube of that anti-friction oil for clutches? The front diff calls for 75w-90 standard not synthetic gear oil like the rear diff...

I tried putting in some of the limited slip anti-friction oil and saw no positive results. I'm wondering if when the previous owner changed the diff. cover, the wrong weight oil was put back in. The dana 50 in a super duty calls for standard 75w-90. The oil in the rear now looks very clear with a slight green tint to it (which to me seems more synthetic then the slightly transparency of standard gear oil.)

If the wrong gear oil was used, could this lead to the failure of the limited slip (or whatever it is) carrier?

Please help as I need 4wd to drive, as my truck is HORRIBLE in the snow with 2wd.

 

have a 2001 f350 super duty.
when i engage the manual locking hubs and attempt to use 4 wheel drive i get the same sound u describe, but the difference is i have no front wheel drive. like u i thought it felt like a uv joint, but i figured the 4x4 would work.
asked my mechanic and he said the chain in the front diff might have gone, and he would get a used one and install for $850.00.
but he said he would want to get it up on the lift to confirm, i trust the guy and he always treats me fair. he is a good mechanic, but not a heavy duty truck expert.
i told him i would get back to him.

anyone with any theories.

 

there it's a chain in the front diff. The front diff is just like the rear on the superduties, it's a ring gear on a carrier/differential and a pinion gear. I would take a good look at the ball joints and stub shafts. it's possible and somewhat likely that the yokes of the axle shafts are impacting on the ball joint studs.