Hello all! Im new to the forms and I just got me a 05 fx4 and I love it!

Yesterday though I started to hear a slight hum that seems to be comming from the rear diff. The noise only appears when im on the gas for a prolonged perriod of time like after 10 minutes on the freeway (not stop and go on the street). I got underneath and there seems to be oil on the top and underside of the rear diff where the drive shaft enters. There is not alot and it doesnt look very fresh. I wana do a service on it but ive never worked on a differential before so I dont know what to look for.

Any ideas as to what this may be or what I should look for?

Thanks!

 

I just changed that rear diff pinion seal on my 05 F150. It was surprisingly easy if you're a do-it yourselfer. IF you want the documents I used, I can email them to you.

The hum, I'm no expert, gonna say your diff gears are wearing out. you may have run it out of oil. Regarless, your diff cover has to come off, then you can have a look for anyhting funny, do a backlash measuement on the gears, and change the seal all at the same time. or take it in, I Was quoted like $265 to change the seal, but I did it myself. it's a $15 seal and $75 worth of oil.

 

I presume your truck has some miles on it. The noise you hear, a whining noise under load, but not coast, is due to loss of pinion shaft bearing preload. The bearings have worn a bit allowing the pinion gear to dance around.
The bearing preload can be re-established and the noise reduced with a fairly simple procedure. I can outline it here, but you can find the procedure for yourself:


BTW: Used bearing preload should yield 8-14 lb/in of running torque.

Have fun.

 

Thanks Guys! Took it to a buddy of mine who works in a shop and we changed the pinion seal just this morning. Took bout 15minutes with a lift. I was a little over half a qt low on fluid also. He felt the bearings are a little worn because of the movment in the pinion. Could this just be becuase of a pre load issue? and if so I dont understand what that is so I need some explaining.

 

Setting clearance and position of the meshing teeth of a hypoid gear set is critical. That's why the pinion shaft bearings must be proloaded. Tightening the pinion shaft nut squeezes the roller bearing cones together and forces the rollers into the inside and outside races. The preload guarantees that ALL slack is taken out of the mesh between the rollers and races so that the pinion gear doesn't move about and mess up the critical settings with the ring gear. The proper preload is determined by the amount of drag the preloading force puts on the bearings. That drag is measured with a dial torque wrench, the type demonstrated in the video. There are other means to measure the torque, but you must be clever with lever-arms and weights.

The crushable spacer inserted between the pinion shaft bearings helps maintain that critical preload once it is established......Don't forget: Running torque for used bearings is 8-14 lb/in.

 

Ok its makin sence now! Thanks for the explanation I like to fully understand a project and why things happen the way they do.