Hey All,
On the Amsoil website and they list 3 different Limited Slip Ring Gear sizes: 8.8, 9.75 and 10.25.
I have an '07 FX4 w/the 5.4 and 3.73 limited slip rear end w/the tow package. Is there a tag and what is the code?
Any opinions out there on Amsoil?
I've been running Mobil1 and changing it around every 3k miles and the new to me local garage recommends Amsoil w/10-15k oil changes!!!!!!!!
I also changed all the fluids at 50k and I am quickly turning 100k so it's time again for the diffs and xfer case fluid changes. I had a synthetic put in last time but not sure what. Going to go w/Amsoil this time around.
Thanks.

 

There would be a tag on the rear diff itself. If your truck is a 5.4 with 6 lug wheels, you have the 9.75.

 

The absolute BEST oil and filter for a 5.4 3 valve is Motorcraft semi-synthetic 5w20 with a Motorcraft filter, changed every 3 to 5k. You are fine using Mobil 1 or Amsoil, but I wouldn't leave it in any longer than 5k due to the VCT system sensitivity to contamination.

Amsoil for the gear cases is excellent. 75w140 in the rear with Ford friction modifier, 75w90 in the front, ATF in the TC and tranny.

If you have the HD payload option with 7 lug wheels, you may have a 10.25 rear.

 

Thanks Guys!

 

There is also a code on the sticker on the door jamb that tells you what rear and trans, etc you have.

 

The door jamb sticker only identifies the axle ratio and whether it's limited slip or not - it doesn't identify the ring gear size. However, the tag on the axle itself identifies size too.

 

Or just count the bolts.