Hi, I have a 2001 4x4 F150 supercrew with 60K miles on it. I was wondering at what milage are people changing ther diff oil?? The manual say at like 90K or something and of coarse the oil change places try to get you to change it at like 30K. I do a lot of 4x4 which I know strains the tranny and tranfer case oil. I have also submerged my diffs on occasion. My diff oil is looking very black and Im think of changing it. So far I have only service the Tranny at 30K.

 

I changed mine at 6000 and again at 6500 only because I did a gear swap then. It does not cost that much in fluid so I would do in now if I were you with 60k on the clock.

 

If you have a traction lock rear, it has expensive synthetic lube and it is supposed to be good for life. It costs about $15/bottle at the dealer and you need over 2 1/2 qts plus friction modifier. The cover gasket is RTV, so let it cure a little before you bolt it back on or it may leak.

 

If you submerge your axle regularly, you should check for signs of water in your rear end lube often. If I had 60K on the clock under severe usage, I'd forget the recommended intervals and change it now.

 

If you're running 75W140, whenever the rear axle has been submerged, as if launching or retrieving a boat. Otherwise, unless you're one of the "better safe than sorry" guys, I'd check the level every now and then and leave it be. Last time I was in my 9.75" in my '97 was about 80K miles ago.

If it's plain jane 90W, I'd go every 60K miles or so.

 

I did my front and rear differentials and transfer case at 60k, if you 4x4 a lot I would do the same.

 

i bought my truck with 30k on it and checked the diffs at 35k and the front was the consistency of gooooood chocolate milk and the color was GRAY.....the rear was a little thicker and a little darker.......my point is stick your pinky in there and check it, then change it i'm changing mine a minimum of twice a year due to slightly heavy off roading. good luck

 

I would go ahead and change all the fluids and be done with it. I just did it at 70k on my truck and the stuff that came out was pretty nasty. BTW Amsoil series 2000 gear lubes have the friction modifier already added in for use in an LSD.