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Synthetic Gear Oil

4.1K views 18 replies 10 participants last post by  waltman  
#1 ·
I am about to swap in an 8.8 Trac-loc differential and am wondering what gear oil to use. I am thinking of switching to synthetic since you don't need to change it that often. So, first off, what brand of synthetic is best for gear oil? And second what weight should I use? 75w-90? 75w-140? 80w-90? 80w-140? Do the back and front diffs take the same weight? And with the L/S, if the oil says it has friction modifier in it already, should I still get a bottle and add it in? Also, how much oil do I need to get? In addition, im changing the fluid in the transfer case. Which is ATF is best? Should I use synthetic?
Thanks-
 
#2 ·
Mobil 1 75w90 synthetic. Get 6 quarts. And stop by your local ford dealer to get some friction modifier. The front and rear diffs take the same oil. Use mobil 1 synthetic atf in the transfer case.
 
#5 ·
Cool thread. :)
x2 so far. :)

For ATF-using manual transmissions like a ZF, those that's BTDT
recommend Red Line's MTL 70w-80. It's kinda like synthetic ATF
that's been formulated for AFT-using manual transmissions and
transaxles.

www.redlineoil.com

-------------------------------

What was the question again? :/

Mobil-1 75w-90 for an 8.8 or Ford9inch with Traction Lok.
But with an Eaton TrueTrac don't use synthetic.

Asdaven, are you going with Ford-Racing's carbon disks? :)

Alvin in AZ
 
#6 ·
6 quarts total for both differentials? Im just going to do the rear for now. They were just changed, but im getting a new rear end. So, thats only 3 quarts then? Do I leave some of the oil out adding the friction modifier? So, Mobil 1 75w-90 instead of Mobil 1 75w-140? I read that ford started reccomending 75w-140 over 75w-90 in Mustang 8.8's? And Mobil 1 ATF for the transfer case? How much does the transfer case hold?
Thanks-
 
#7 ·
damn dude.........75-90 mobil 1 gear oil. put the friction modifier in first, fill up until it pukes out of the fill hole. mobil 1 atf for transfer case. fill method is the same as the rear end.

your owners manual should have the specs for fluid capacities, if you don't have it, search it here.

and yes it's that simple, not everything about car repair is 100485045 steps.
 
#8 ·
In my manual, it says "Hypoid Gear Lubericant". In another manual, its says "90W". What does that mean? So, 75w-90 over 75w-140 won't be too thin? How come ford is saying to use 75w-140 now? And the mobil 1 ATF will lube the transfer case good? Thats the reason im going to synthetic is better lubrication.
Thanks-
 
#9 ·
75w140 is for heavy duty shit. all i've ever used is 75w90, it's fine dude, take a xanax or something.
 
#10 ·
Hypoid gear oil just refers to a type of oil made for hypoid gears, which is just how the gears were cut. I have not seen any gear lube recently that wasn't suitable for hypoid gears. 90w is just the recommended viscosity. You will be just fine with 75w-90, 80w-90, or anything close. 75w-140 is unnecessary, Ford used 80w-90 for many years in the 8.8" with no problems.

Make sure you use motorcraft friction modifier.

And yes, the Mobil 1 ATF will lube your transfer case just fine.
 
#12 ·
Okay 75W-90 Mobil 1 it is for the rear. What about Mobil 1 synthetic ATF in the tranny? I read somewhere that it is too slippery for the clutches in the older ford transmissions. I also read that synthetic might be too slippery for the transfer case also. But, im not sure. I want to use the best fluids for the truck and synthetic is not always best.
 
#16 ·
But, no one has had problems with burning out clutches in the tranny with synthetic ATF or burning out L/S clutches with the Mobil 1 Gear Oil and Friction modifier? I read something about our AOD trannys needing Mercon and not Mercon V, even though Ford says Mercon V is okay, some claim its not. So, my concern is isn't Mobil 1 Mercon V?
Thanks-
 
#17 ·
The M1 ATF stuff is compatible. They even make a DexMerc version of it but I've not seen it in stores. I've only found the M1 ATF in the local stores. If I recall right the DexMerc is in a blue bottle.
 
#19 ·
I am about to swap in an 8.8 Trac-loc differential and am wondering what gear oil to use. I am thinking of switching to synthetic since you don't need to change it that often. So, first off, what brand of synthetic is best for gear oil? And second what weight should I use? 75w-90? 75w-140? 80w-90? 80w-140? Do the back and front diffs take the same weight? And with the L/S, if the oil says it has friction modifier in it already, should I still get a bottle and add it in? Also, how much oil do I need to get? In addition, im changing the fluid in the transfer case. Which is ATF is best? Should I use synthetic?
Thanks-
Change it so often? Just how often do you or anyone change the oil in the diff? I have never done it myself...anyone else?
I just went with regular gear oil in my rebuilt diff with the additive that Ford recommends. Also, the gear oil that says the additive is already in there does not work as well as the Ford additive. I found that out after I did mine.
 
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