Rear End Fluid.

[ICUFFEM]

Does anyone know if you can use a synthetic fluid in the front and rear diff? Like a royal purple or amsoil? I know with regular fluid you need the friction modifier, but I was wondering if you needed it with synthetic fuilds?

 

[gtbutler]

ICU,
You can use full synthetics in both differentials. In fact, pretty much everyone in the forum would probably agree that the only thing they would put back in (when doing a gear lube change) would be a synthetic. As for brand, Mobile1, Amsoil, RoyalPurple are all great brands. As for the friction modifier, check your axle code to see if you even need it. The axle code will be on your vehicle sticker (check that vs. axle type chart)' limited slip rear ends (which aren't on all vehicles) are the only ones that call for the friction modifier. It won't "hurt" to put the friction modifier in an open axle. 75W-140 in the rear and 75W-90 in the front if you have 4WD. It's a real easy DIY job. Make sure you can loosen the fill plug before you remove the drain plug (there are some horror stories when some have drained the fluid and couldn't get the fill plug out, which means a tow to the local shop to remove the plug).

Have fun!

 

[ICUFFEM]

I will check that axle code, but the thing I was questioning I guess is that the Royal Purple gear max says it has a friction modifier added to it. I was researching it on their website. I have an eddie bauer 04' awd. I don't know if that makes a difference or not.

 

[Exproblems]

I will check that axle code, but the thing I was questioning I guess is that the Royal Purple gear max says it has a friction modifier added to it. I was researching it on their website. I have an eddie bauer 04' awd. I don't know if that makes a difference or not.

When you get your exact rear diff "axle type or axle code", it should be a 2 charcter code off of your door tag, then use the list below to determine if you have an "open diff" or a "limited slip diff". If you have a "limited slip diff", you need to add at least 4 ounces of friction modifier according to Ford. You can buy a 7 ounce tube of it in parts stores for around $5-$7. The Limited Slip rear diff's hold 1.60 quarts of fluid and the Open Diff's hold 1.75 quarts of fluid. The rear diff "check/fill plug' torque is 25 ft lbs. The front axle (4 WD) lube is SAE 80W-90 and a synthetic brand is fine for this as well. If you are going to use "Royal Purple" and are unsure if it contains enough friction modifier in it for your type of diff, if it happens to be a limited slip diff, I would phone the company and speak to a rep in person just to be sure you do not need to add additional friction modifier with their product. With an Open diff, you can still use a product that contains friction modifier, it won't harm a thing.

Rear Diff Codes:

Codes:

42- 4.10 Gears Open Diff
45- 3.55 Gears Open Diff
46- 3.73 Gears Open Diff

D2- 4.10 Gears Limited Slip
D4- 3.73 Gears Limited Slip
D5- 3.55 Gears Limited Slip

 

[ICUFFEM]

Thanks so much for the axle info! It was a great help and I have axle code 45 so I bought a regular synthetic gear lube by valvoine. It says it meets ford standards on the bottle so I think I'm gonna be fine. To bad I have an open diff though, explains my crappy performance in the mud lol guess it's time to lock it up.

 

[Exproblems]

Thanks so much for the axle info! It was a great help and I have axle code 45 so I bought a regular synthetic gear lube by valvoine. It says it meets ford standards on the bottle so I think I'm gonna be fine. To bad I have an open diff though, explains my crappy performance in the mud lol guess it's time to lock it up.

Your welcome, no problem, glad it helped. If you got the 75W-140 Valvoline synthetic you are okay. I went with Mobil 1 synthetic at $18.95 per quart. Ridiculous how expensive that stuff is, but it is good stuff. I also have the code 45 diff, 3.55 gears, open diff, but I don't off road with my Explorer(just snow in winter), just get $hitty mpg in the city. On the Thruway I get 16.8 mpg. BTW, from your screen name, are you a cop or a C.O.? I was a C.O., but retired now.

 

[JohnnyO]

The factory puts in synthetic diff lube anyway.

 

[ICUFFEM]

Exproblems, you are right the stuff is expensive! Oh well. I started getting better mileage after I put in a k&n drop in filter and the E3 Diamond fire sparkplugs, as for my screen name, yes I am a C/O I work at the dreaded Stateville C.C. in Illinois.

 

[Exproblems]

I started getting better mileage after I put in a k&n drop in filter and the E3 Diamond fire sparkplugs, as for my screen name, yes I am a C/O I work at the dreaded Stateville C.C. in Illinois.

I did the K&N air filter thing and didn't see better gas mileage. I also did a full tune up, fuel injector cleaning and it didn't make my Ex that much better in mpg. This Ex just sucks in the city for mpg.
On the C.O. thing, I kind of figured from your screen name. I think I have heard of Stateville CC. I worked at the NY state max security prison "Attica CF" for 12+ years, then transferred to a medium security prison named "Wyoming CF" where I made SGT., located right behind Attica CF, then transferred again to my final jail called Gowanda CF. I retired as a SGT with 25 years in the Dept. Stay safe out there Icuffem!