Posted this in 2004-2008 F150 thread as well, didn't see the Expedition/Navigator thread.




So here is the basic run down of what is occurring. From cold start, have a howling noise coming from transmission/transfer case. Seems to slip between 35-45mph if you let off throttle and try to accelerate ( imagine driving through a sharp curve in the road ). This all started happening after locking truck into 4lo to pull neighbors truck out of mud. Noise has progressively gotten worse over the last several weeks. Finally was able to wrangle the truck away from the wife to bring to my shop, got all 4 wheels off the ground and put it in drive. Noticed the front drive shaft is spinning as fast as the main driveshaft, but front wheels are not spinning. I began to think maybe the transfer case was stuck in 4wd, so I ran it through all ranges of 4wd and heard the click/clunk at each activation. pulled drain plug on transfer case and fluid was dark red/brown in color. drained and refilled. Checked trans fluid, bright red, so left it alone. unhooked battery and reconnected after 10 minutes, drove truck about 40 miles down highway towards home, howling all the way. Got to the turn off to my town and was caught by red light. sat there maybe 3 minutes before making my turn. Once I turned, no howling, converter went into lock up and ran/shifted perfect. got in truck this morning and the howling, no converter lock up happening again. This truck usually runs about 1,000-1,200rpms at 65-70 mph, and with this issue it is running 1,500-2,000rpms at highway speed. Any ideas are greatly welcomed.


Thanks,


Matt

 

There is a separate forum for 2007+ Expedition/Navigators here: 2007 - 2014 Expedition & Navigator - Ford Truck Enthusiasts Forums

If this is a common problem for your year they might already have an answer for you.