Oil for rear?

[Car RamRod]

Hey people Im in the process of putting my 3:55's in. What I'd like to know is what type of oil do I need to use, and what is this friction modifier everyone keeps talking about?
Thanks alot

 

[TrophyHead]

Friction modifier is an addivite you put in to help your rear-end form chattering or something along those lines. If your running regular gear oil you'll need it. Some synthetics do not require the friction modifer. I *believe* it is 75-120W....but some synthetics are different. Ask the parts guy for the correct oil weight or search.

 

[maverick0716]

I have Redline 75W90 in mine...it came with friction modifier already in the oil.

 

[jerryD]

just get a bottle of modifier from your local ford dealer, and then get some 80-90w gear oil.

 

[89MustangGX]

If you have a Trac-Lok you will need friction modifier. As mentioned above, it may be included in some of the synthetics.

I have run Mobil-1 as well as Amsoil and both have worked fine for me.

 

[HISSIN50]

I might run some dino oil in there initially (with FM) and then once you break the gears in, change it out to a synthetic of your choice.

Good luck.

 

[89MustangGX]

I might run some dino oil in there initially (with FM) and then once you break the gears in, change it out to a synthetic of your choice.

Good luck.

I like to change the oil shortly after new gears are put in there as well, in case any shavings, etc. come off initially. There's certainly no reason to run expensive synthetics just to change it out so quick if that's the way you decide to go. But after that -- I vote for a synthetic oil.

 

[Car RamRod]

theyre not brand new gears; theyve got about 40k on them. What synthetic would you guys suggest?

 

[89MustangGX]

Any synthetic shoul work well -- as I mentioned above, I have used Mobil-1 and Amsoil before, and have used dino oil before as well. Can't say I ever noticed a difference, but it's one of those things you just know is better to do.

 

[Car RamRod]

thanks guys Ill see what I can get next trip to the parts store.

 

[HISSIN50]

Exactly, you are not gonna go wrong with any quality synthetic. I go with what I can get locally at a decent price.

Good luck.

 

[TRWXXA]

I recently changed my gear oil. At the Ford dealership where I went to get the modifier, they said that my 'Stang required 75-W140 synthetic even though the manual specifically calls for 80-W90.

The parts guy was all too happy to offer me Motocraft 75-W140 at the bargain basement price of $23/quart!

80-W90 dino oil from NAPA ($5/quart) seems just fine to me.

BTW: Make sure you open up that 4 oz. bottle of friction modifier in a well ventilated place, and that you don't get any of it on you. IT SMELLS AWFUL!!

 

[HISSIN50]

Redline makes 75W-140 or 85W-140 as I recall (it is what I am gonna use next time).

 

[qplk11]

You may find this interesting.
http://www.bobistheoilguy.com/images/lucas/lucas.htm

 

[crazypete]

Look at it this way....how often are you gonna change the rear end gear oil?

Like....once every few years?

Even if the synthetic makes 1% extra economy, power from reduced friction, it will pay for itself many times over PLUS, the synthetics dont need friction modifier.

FM is the bane of my existence. It is hands down.....the smelliest stuff ever created by man. It's like the deepest, most penetrating and persistent stench of......pine tree sweat burnt oil. Its horrific!! Avoid it if you can. You'll get a taste of it when you pop the diff open.

Hey, rebuild the tracloc while you are in there.....easy, $50 for the clutches and you basically have the thing already apart so you just need to rotate the spiders out, yank the clutches, put the new clutches in and rotate the spiders back in.

 

[Car RamRod]

ah its a fairly low mile rear that came off a chick car, Im sure the clutches are ok.

 

[00FourSixGT]

Well I'm doing a gear swap too. I have a bottle of friction modifier and this oil

Am I going to be ok using these 2 things? I was also told that our differentials require synthetic oil..

 

[HISSIN50]

AFAIK, the factory fill of fluid in the rear end is conventional fluid (not synthetic).

 

[bryanrevans]

00fourSixgt does the back of that bottle say "Does Not reccomend adding friction modifier" I think I saw that at Walmart.

 

[jerryD]

that oil is fine. i used that stuff with the modifier for my eaton posi. your gonna need another quart of oil if you still have the stock cover. more if you are going with a aluminum one.