i own a 89 f-250 4wd 351C, inside the front axle there is a clunking sound that occurs only when the 4wd is engaged and the wheel is turned past half way while driving. i beileve the diff fluid is running low, and any insight on what this problem could be will be much appreciated, i need this truck to be running for the winter storm coming so i can plow

 

Not familiar with any operating differences there may be between the F150 and F250 - so, I'll share my thoughts as applied to my F150.

Inspect the u-joints - both for the driveshaft and the axleshaft. The axleshaft joints did not come with grease fittings, so considering the age of the vehicle, these may be at end-of-life.
The 4WD front end needs to be able to slip a little on turns, otherwise things bind up, get wheel hop, a lot of grunting and groaning, etc.
If the diffy fluid is low, obviously, fill it back up. This is important for seal and bearing lubrication.
Make sure both hubs are engaging. If one side is not completely engaging, may be getting some hub noise whenever the axle and wheel speeds differ, such as during turns.

 

i checked the cv's, axles, u-joints, and driveshafts and there all fine,i lifted the truck up with all four tires off the ground engaged the hubs, started the truck, put it in 4wd-then put it in drive, and the driver side tire seemed to be spinning faster then the rear driver side tires, but the front passenger side tire was hesitating to spin if any at all, i looked at the diff fluid and it was low, so i fill it up. Through the driver side axle it leaked out onto the lower ball-joint at a very fast rate,(with in a minute everything i put back in went out onto the ground) so the driver side seal is gone, so it basically has had no diff fluid, and i have driven the truck on a few very brief 'test-drives' with little to no fluid "would that mess up the diff to do what i described?"

 

Since the front passenger side tire wasn't turning - then the driver side has to make up the difference by spinning upwards of twice as fast as the rear wheels. What you describe doesn't sound normal, but I don't have a lot of experience with the inner-workings of Ford front axles.

Can you rotate the passenger side tire with the hubs locked, wheels off ground, and tranny in neutral? How does that compare with rotating the driver side? Wondering if something on the passenger side of the axle is bound up? It could be something as simple as the brake drag is greater on the passenger side - may try to rotate the wheels with the hubs unlocked, and compare between sides.

For the fluid to leak out that fast, wondering if perhaps there isn't a bearing failure that wiped out the seal?? Seals usually ooze first, then drip - which you should have noticed through its failure cycle, but an out-n-out flood of oil seems that things got extreme rather quickly.

I know all of this isn't what you want to hear, and I am just speculating here.

 

that what i figured about that one wheel that was hesitating to spin, but while the truck was not running i checked to see if both wheels would spin equally, but,, i locked the hubs engaged the 4wd in park though, but both wheels spun equally in one direction and the other wheel in the opposite direction, but i didnt think to put it in nuetral, i will do it in nuetral tomorro to check for any differences, but if that dont change in going to take apart the whole front axle peice by peice to see whats wrong and if i dont find anything wrong im going to replace the differential, because i need to figure this out before the snow hits otherwise my plow truck is useless any other insight will be greatly appreciated