Front/Rear Differential Fluid Type

[gogurtruiz]

Hi guys,

Sorry if this has been asked before but I looked throughout the forums and couldn't seem to find a clear answer.

Looking to change the fluid in my 1998 5.0 AWD Limited with close to 250k miles. Not sure what the axle code is.

What fluids are recommended, specifically for the front differential? Any changes for a car this old with this many miles?

I know the manual calls for 80W90 in the front, and 75W140 in the rear (if I'm reading this correctly, since I have a 5.0). I don't believe any friction modifiers are needed for my car, but I could be mistaken.

I'm planning on using synthetic for both, but just want to know if I should mix viscosities per the manual, or can possibly use 75W140 for both.

Thanks in advance!

 

[410Fortune]

80w 90 or better yet 85w-140 full synthetic
Both front and rear diffs you can run the synthetic lube

Friction modifier is only needed in the rear with the limited slip differential

Your 5.0 is most likely 3.73 limited slip

The friction modifier can be used without a limited slip as well… it helps prevent foaming even when no traction device is present

These trucks shipped from ford with 80w-90 in the diffs until I think 98 when all fords across the board went to 85w-140 in an effort to increase mpg and meet epa standards. When the switch happened the dealers only carried 140w full synth… the same differentials can run both fluids

Your front differential is incredibly difficult to drain if not impossible without removing it from the truck

I drill out the inside of the bottom most
Bolt on the front cover, at an angle pointing up into the diff with a 1/4 drill bit
thus creating a drain and the fluid can be changed, a little thread sealant on the bolt when it goes back in. Ford should have e shipped them with a drain

 

[donalds]

Excellent modification

 

[C420sailor]

That’s brilliant. Doing that the next time my front diffs are out.

Or maybe I’ll just drill the housings and tap for small NPT plugs? Idk. Either way, got me thinking

 

[SofaKing95]

Genius

 

[gogurtruiz]

80w 90 or better yet 85w-140 full synthetic
Both front and rear diffs you can run the synthetic lube

Friction modifier is only needed in the rear with the limited slip differential

Your 5.0 is most likely 3.73 limited slip

The friction modifier can be used without a limited slip as well… it helps prevent foaming even when no traction device is present

These trucks shipped from ford with 80w-90 in the diffs until I think 98 when all fords across the board went to 85w-140 in an effort to increase mpg and meet epa standards. When the switch happened the dealers only carried 140w full synth… the same differentials can run both fluids

Your front differential is incredibly difficult to drain if not impossible without removing it from the truck

I drill out the inside of the bottom most
Bolt on the front cover, at an angle pointing up into the diff with a 1/4 drill bit
thus creating a drain and the fluid can be changed, a little thread sealant on the bolt when it goes back in. Ford should have e shipped them with a drain

View attachment 464516

View attachment 464517

Thanks for your response!

This is a great tip indeed, and appreciate the heads up on the 85W-140.

I was thinking of going the fluid pump route — just open the fill plug, out with the old, in with the new. Would I really need to remove it just to go about it that way?

 

[410Fortune]

Nope you can always pump new fluid in and hopefully get some of the old out
I was just sharing what I do around here
After 273k miles my front differential gave up and I had to replace it.