75w140 Gear Oil for F150

Joined
Jul 25, 2003
Messages
124
Location
Franklin, TN
BITOG.... I've come to make the proverbial mountain out of a molehill in regards to a gear oil choice. I have a 2004 F150 that I recently purchased with 125k miles. It has a 5.4 liter engine and is 4x4. It's in great shape in and out, and runs well. The manufacturer says the axle is "lubed for life", which I'm sure incites some hearty debate. The trans fluid looks/smells fresh, so it's been serviced recently. The axles however show no signs of ever being serviced (no tool marks on the fill plug, cover looks to have never been off). So I'm interested in replacing the fluid in the front and rear axles. Usage- weekend trips close to home, possibly some medium towing (5k pounds) infrequently. In doing some background research on gear oil, the owners manual specs a 75w90 synthetic "fuel efficient high performance" gear oil. I cannot find it anywhere, and along the way found some TSB information online that years ago Ford advised its dealers that the aforementioned oil should not be used, and instead a 75w140 synthetic should be used (and even went so far as to say the tag on the rear end specing "XY-75W90–QFEHP" should be scratched through). I have narrowed it down to 2 (open to more suggestions though), and would love to hear your feedback: 1) Motorcraft 75w140 synthetic (XY-75W140-QL). Pros- I find some value in using OEM fluid in the vehicle, and have been impressed with what Ford/Motorcraft has done with their oils and filters. If they have enough confidence to say "lubed for life" I would imagine it's a great oil. Cons- About $5 more expensive per quart than the other choice below, plus it appears I'll also have to buy some friction modifier. 2) Mobil 1 75w140 synthetic. Pros- have used mobil 1 in the past with good success, feedback from others using it are always very positive, less expensive than the option above, and already includes friction modifiers for limited slip. Cons- not OEM fluid. Thoughts?
 
Joined
Aug 5, 2015
Messages
34
Location
Rocky Mountain West
I recently used some Amsoil Full Synthetic Extreme Gear lube to change out the F/R diff's in my 04 Dodge 3500 4x4. So far, so good, and it was no more expensive than locally sourced M1 when ordered direct from Amsoil. They have a 75w-90, 75w-110, and 75w-140.
 
Joined
Aug 12, 2013
Messages
1,039
Location
Alberta
I have a 2009. I changed the differential fluid on both axles when I first bought it with 122k kms (70k miles). I used redline 75w140 in the rear along with a bottle of redline friction modifier for the limited slip clutches. in the front I used mobil 75w90 of some sort that I can't really remember. Both axles have been fine for the last 30k miles with those fluids. That being said, I would simply use the Motorcraft 75w140 in both if I ever feel the need to change it again. Find out what rear axle you've got and whether it has a LS differential. I would add a bottle of friction modifier regardless of what it says on the bottle (some claim to have the modifier in them already). Chattering clutches are no fun.
 
Joined
Sep 25, 2013
Messages
1,566
Location
St. Louis, MO
Use either: Amsoil Severe Gear 75W-140 Mobil 1 LS 75W-140 If your rear diff is a limited slip it is specified that both the above gear oils have LS friction modifier. It you get rear end chatter, you may need to add some additional LS additive. Next would be either to pull the cover or suck the fluid out, your choice, but sucking it out if you have a Mityvac would be easier. For the front diff, the spec is for 75W-90, Amsoil and Mobil 1 make that viscosity as well. I don't know if Ford front diffs have a drain plug, so you may need to suck the fluid out of there. Good thing is the fron diff will not be limited slip so no modifier needed.
 
Joined
Sep 26, 2010
Messages
9,105
Location
Houston, TX
I am not sure what year they came out with electronic locking differentials in F150s, but if yours has a knob on the dash that you pull out to lock the axle, you will not need the friction modifier. I have used Motorcraft twice and Amsoil twice; the 4th OC is currently in the axle and you can see the UOAs here. I did not buy into the "lifetime" fill statement, dumped the FF at 13K and was glad that I did. Tons of iron in it, but despite longer runs for each of the subsequent OCs, the iron has gone down. With your mileage, I would use Amsoil in both axles (75W-140 in the rear and 75W-110 in the front) and call it good for about 100K.
 
Joined
Jan 6, 2009
Messages
1,625
Location
Watertown, New York
Originally Posted By: donnyj08
Amsoil SVG 75w140 and Amsoil slip-lock 2nd choice would be 75w140 Synpower LS
+1 Those would be my exact choices as well!
 
Joined
Dec 12, 2002
Messages
43,676
Location
'Stralia
Bear in mind that since your truck was built, they have messed with J360... J360 not as it was in 2004 so you can now have a 75W110, which is at the top end of what a 90 used to be allowed to be, and the 140 maximum range has shrunk down, used to go to 41cst, now 32.5cst, and 190 taking over. I'd personally go 75W110, which is what would have been the very thick end of 75W90 when your truck was built.
 
Joined
Aug 12, 2012
Messages
3,513
Location
Cincinnati, OH
Originally Posted By: midnightlaundry
Amsoil SG has the LSA in it already. I put 2 quarts in my Explorer. It cost me $37 bux tho... Stuff is not cheap.
ouch.. you need to get hooked up with Pablo here. you paid way over retail for those two quarts. ~15 retail is a good price. ~11.50 as a PC/Dealer I believe. Get Pablo to hook you up. He is the site sponsor. I know it has the LSA in it, but sometimes you need a little extra especially In ford diffs. I generally just add the slip-lock in 1oz increments until i have absolutely no popping. I just did a diff service and outer axle bearing and seal replacement on my dads 9.75 F150 and i had to add a couple of ounces of Slip-lock to the fluid.
 
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Joined
Sep 17, 2002
Messages
4,949
Location
Lakeville, MN
I'd run the cheaper or easier to source of two fluids the OP mentioned. Both are fine. My truck is an '04 that came with 75w90 from the factory, but due to pinion bearing noise was refiled with 75w140 and tagged accordingly per the TSB from Ford when repairs were made. Always found it odd that Ford even went back to 75w90 when these trucks came out - the previous generation came with 75w140 as factory fill. Also note that even Amsoil recommends their 75w140 product in the rear end in these trucks, not the 75w110 product.
 
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