Hi all,

I have an 04 4.6 2wd 3.73 gears. When do I need to change the rear end fluid?

TIA
Stan

 

Theorically, you don't have to change it for the life of the truck. The fluid is only to be replaced if there's an internal failure of the axle or the axle's been submerged in water, as if launching or retrieving a boat.

But if it makes you feel better, every 100K miles or so should be more than often enough for service.

 

I have read where that if you are going to change the fluid you need to do it at 35K and then every 35K from there on out. Other wise changing it some 100K miles later is asking for trouble. The other solution is to not change it. Technically it is a "lifetime" fluid. With all that heat down there in the diff. I dont see how the fluid would break down over time, not to mention after 100k miles. I'd change it if it were me.

 

You shouldnt have to change it anytime soon unless you are hacing problems with it. If it makes noise or clunks than that could indicate you are low on fluid but you dont really have to change it like you change oil.

 

Thanks for the response so for guys.
I guess I should have included why I asked. I got the oil changed today and the plug had considerable "shavings" The lube was dark grey/green but I'm not worried about the color per se as that could be the color it is supposed to be but the shavings did catch my eye as I spent several years working in lube shops.
I read the maint book and owner's manual but it really wasn't clear.

Thanks
Stan

 

shavings on the plug is completly normal. its larger chunks you need to worry about

 

The only people I've ever heard say change the differential fluid were the service guys at a Ford dealer.

Unless you're swapping gears or something, it should last for a very long time.