Recently repaired the acceleration clunk noise a 03 Mountaineer AWD. Sounded like a jackhammer under the truck when taking off, worse when going uphill or under a heavy load.
Before this the front pop shaft CV joint had begun binding up, to the point whole truck was vibrating. Rebuilt the shaft with new CV joint, only for the front yolk to shear a week later. This failure took out a chunk of the trans bell housing, damaging the pan which also crushed the solenoid pack. So had to replace entire shaft anyway. Fortunately could salvage the solenoid pack, only a few traces had been broken so just needed minor electrical repair.
Did also replace rear u-joints. Had slight play causing some vibration at highway speed. Though not related to the acceleration clunk. Didn't mess with the shaft's slip-yolk. Believe that was more of an issue with later F-150's. Even after 300K on the ODO that movement was smooth.
Resorted to pulling the transfer case and replacing the chain. Theory being it got stretched when the front shaft had the binding issue. Though the jackhammering didn't start until several months after previous repairs had been done. Side by side couldn't see any noticeable difference in chain length between old and new but replaced it anyway. Also of note, the output shaft splines were a bit rusty. Removing the T-case was a light struggle and greased them thoroughly on reassembly. Also noticed slight play in the planetary gears. Play was ~.5mm for all four though spun smoothly. But needed truck back on the road, couldn't wait to order a new one and gambled on it still being in spec. ~75K prior I did have the T-case apart to replace the viscous coupler. Not my first rodeo having that apart. A shout-out to STE Couplers. Their reman has been holding up well.
So can't be sure if it was in fact the chain stretch or rusted shaft splines but after all this the Explody is driving driving better than ever.
