I have a 2001 F-150 Supercrew with a 5.4, 121000 miles, and it has the tow package. For the last couple of weeks i have noticed a loud whine coming from the rear of the truck. I took the wheels off today and checked the brakes, they are fine. I put the truck in neutral and turned the axle and hear grinding and whining coming from the rear end. I had this rebuilt by the ford house at around 80k. Is the rear end going out again? I am going to figure out how to check the fluid. Any help is appreciated.

 

The bearings probably are failing but odd for another rebuild at 40k after the first. To check the fluid use a 3/8s extension to remove the fill plug on the driveshaft side of the rearend.

 

I checked the fluid through the plug on the drivers side rear of the rear end, it came running out when the plug was removed. I seen some posts where they were told to try adding a tube of friction modifier. If i do this will i need to fill up the rear end with fluid after? Or is there another spot to add fluid, or friction modifier? Thanks for the help.

 

Friction modifier should have been added at the last rebuild. It is only a 7 or 8 oz bottle so I think you should already have it in.

 

i agree with friction modifier as a shot, even though lack of modifier usually only causes noise when turning (clutches working). if not that, most likely a pinion bearing

 

i have an f150 supercrew 5.4 Triton with a super chip on it and when i stomp on the gas when it goes to change into 2nd gear it slips terrible but if i dont stomp it it drives fine i have no clue wut could be causing this problem any suggestions...ps this is my 1st ford.