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Old 03-27-2006, 09:21 PM   #1
nezzer
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Recommened rear differential gear oil?

I am going to be replacing a leaky seal on my rear differential. My 96 5.8L has (to the best of my understanding) an 8.8 rear end with out the limited slip differential.

Another post suggested a 75w-140 gear oil but that was for a 9" rear end. A chain automotive store suggested 80w-90. Which one would you guys recommend?

Thanks!
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Old 03-27-2006, 09:27 PM   #2
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Do you have the owners manual still? It should say in it...
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Old 03-27-2006, 10:45 PM   #3
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Use the 80/90 or 75/90
The 140 is reccomended for very heavy gear loads, such as drag racing and in truck axles
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Old 03-28-2006, 12:42 AM   #4
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i just did mine last week. i used 80w90, get 4 quarts, it says less in the owners manual, but it's wrong. if it is a limited slip, you will know it when you open it up. this is an Ford 8.8 rear differential WITH the limited slip. for this differential, you will need the little 4 ounce bottle of the friction modifier. buy the bottle anyway, just in case, if you don't need it, cool, return it. better to be safe than sorry. if it needs the Friction Modifier, dump the FM in FIRST, then fill it with 80w90 until it comes out of the fill hole, then, you're all done.


Ford 8.8 Limited Slip Rear Differential.

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Old 03-28-2006, 02:59 AM   #5
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80 90 is where its at...take a wiff of that old oil for me...yummy!
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Old 03-28-2006, 10:27 AM   #6
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Nezzer, you have a choice of 4 weights in two types of gear oil.
  • Mineral 80W90
  • Mineral 80W140
  • Synthetic 75W90
  • Synthetic 75W140
Ford has been recommending Syn 75W140 in later model truck diffs. That's the one to use if you want to fill and forget for the next 100K miles. It's also the most expensive at about $13/qt.

The mineral 80W140 is just as good, but isn't as shear-stable as syn, and it won't flow quite as well, if you live in a cold climate.

As was stated, the 75/80W90's are fine in a light vehicle that's not used for towing, but they won't handle shock loads as well as the heavier oils.
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Old 03-29-2006, 02:18 PM   #7
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What friction modifier are you guys using in your LSD?
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Old 03-29-2006, 03:11 PM   #8
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none....

it is used to make the clutches slip so they don't chatter, never had any chatter so i don't run any
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Old 03-29-2006, 08:58 PM   #9
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Hmm, thinking about going synthetic 75w-90 in my 8.8 rear with a detroit.

Think the 75w-140 will be better, even with the detroit, or should I stick with the 75w-90. I don't remember off the top of my head what the detroit needs.
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Old 07-13-2006, 01:35 AM   #10
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Bringing back an old thread instead of making a new one.

I am switching to Royal Purple Fluids in the T-Case and both front and rear gear.

This is a fully synthetic fluid...what weight should I be buying? I looked in the manual and in my Haynes and did not find an answer.

I don't tow and will do mild to moderate off-roading a few times/year.

Thanks in advance for the help.
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Old 07-13-2006, 01:37 AM   #11
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get the 80/90 or the 75/90


Royal Purple has a great FAQ on their site too. Check it out because theres pages about their oils and what weight to run











This is my favorite right here. Hasn't let me down yet so I'll stick with it (plus I like saying I have a full Mobil1 drivetrail)



I run it in every axle I got because everything I have tows something too. I wouldn't even think of running the dino oil in the rear of the SD with that diesel dragging all the weight up the hills.

Last edited by MikE2; 07-13-2006 at 01:40 AM.
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Old 07-13-2006, 01:50 AM   #12
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Honestly I'd have no problem with Mobil 1 either. I ran it in my old Bimmer and I run it in the fiances Lexus. I bet I could pick it up at the ol' Wally world too for a fraction of what RP cost.

Maybe I'll go with Mobil 1...anythings better than what's in there now!

BTW that is a good looking rear diff. Mine is just a stocker 8.8 and will remain so for quite some time!
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Old 07-13-2006, 11:01 AM   #13
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Royal Purple Tranny fluid for the tcase, yea?
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Old 07-13-2006, 06:57 PM   #14
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Quote:
Originally Posted by djdan
Bringing back an old thread instead of making a new one.

I am switching to Royal Purple Fluids in the T-Case and both front and rear gear.

This is a fully synthetic fluid...what weight should I be buying? I looked in the manual and in my Haynes and did not find an answer.

I don't tow and will do mild to moderate off-roading a few times/year.

Thanks in advance for the help.

i guess you didn't read the thread, the viscosities are all over it.

either way, 80W90 for the rear, and i believe ATF for the T-case. at least there was ATF in my friends Explorer.
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Old 07-13-2006, 07:18 PM   #15
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The specs are 80W90 for front and rearends and MERCON in the transfer case. I changed over to Royal Purple about a month ago.
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Old 07-13-2006, 08:50 PM   #16
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If you have a manual transmission that uses the auto fluid, Don't use Royal Purple's ATF. Royal Purple makes a oil specially designed for manuals that need ATF.
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Old 07-13-2006, 09:27 PM   #17
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Quote:
Originally Posted by MikE2
get the 80/90 or the 75/90


Royal Purple has a great FAQ on their site too. Check it out because theres pages about their oils and what weight to run












This is my favorite right here. Hasn't let me down yet so I'll stick with it (plus I like saying I have a full Mobil1 drivetrail)



I run it in every axle I got because everything I have tows something too. I wouldn't even think of running the dino oil in the rear of the SD with that diesel dragging all the weight up the hills.

Just did mine too. Used same
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Old 07-20-2006, 03:08 AM   #18
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Aamco was the last person to do my diff right when I took posession of the truck...what the hell was I thinking? At any rate they did a shoddy job and gooped on the sealer instead of doing a gasket so it had a slow leak as well as dino oil in it. You can see in the pics where it was leaking and rusting on the bottom. I cleaned it all up before I reinstalled the cover. Who knows if Aamco actually even opened it.

Just got done doing mine this evening and it appears I have a limited slip...I didnt think I did! Could someone verify this for me please.

I also found out I do, in fact have 3.55's as it is stamped right on the gear so that was easy.

Ended up using Mobil 1 instead of Royal Purple due to ease of availability and a bit better price. I used 75-90. I did NOT add the friction modifier as the Mobil 1 bottle says its already in there.

When I closed it up I decided to follow someones advice and use a Fel-Pro gasket which was under $5 at Advance Auto. I must say that was a good way to go vs. a bunch of goopy gasket maker crap.

I also decided to clean up the cover and paint it with some hammer paint. It was rusty as hell and looked pretty bad. I wanted to do it black but my black spray paint can clogged.

How hot does a rear diff get?

The paint I used said not to use it on items that go over 200 Deg. F....if it comes off I don't really care..it looks better for the time being.

I also replaced the vss/abs sensor as my speedo needle fluttered quite a bit and my ABS light was going on and off quite a bit even after I cleaned it up and reinstalled the original.

I was also surprised that my diff swallowed 3.75 bottles of fluid. The jacklegs @ AutoZone told me that I only needed three bottles...they even looked it up in the (obviously sucky) database. I had to run to the store to grab another...of course!

Front Diff here I come!

Here be the pics-






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Old 07-20-2006, 12:51 PM   #19
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Cover looks good. I also used Mobile1 when I did mine, although it didnt take 4 qts. That sure does seem like alot...
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Old 07-20-2006, 04:54 PM   #20
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none....

it is used to make the clutches slip so they don't chatter, never had any chatter so i don't run any

I've had a lot of problems with chatter from my rear pumpkin. Usually end up adding some every year or so according to the previous owner, I've had to add since I bought the truck. Stuff works wonders.

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