Diff. Fluid, i know i know just read

[Yomie]

OK i have read and read and read and i cant get a straight answer. I looked in my owners manual and my manual says 80W90, but it doesn't say synthetic or not synthetic, i have the LSD so i have the Friction modifyer to put in when i change out my fluid. Now my question is do i use synthetic or not, i need to know cause i wanna use all synthetics, my differentials are the only things not using Mobil 1 synthetics. Now is it alright to use the synthetics or not?

 

[aldive]

I have 50k miles on Mobil 1 in my diff. No problems whatsoever. Highly recommende it.

Good luck....

 

[Robert]

Read page 224 of your Owner's manual. It will tell you you need 5.50-5.80 pints of Motorcraft SAE 75W140 High Performance Synthetic Rear Axle Lubricant. The limited slip also requires 4 ounces of additive friction modifier C8AZ-19B546-A, Ford specification EST-M2C118–A, but you already knew that part. There is also a metal tag on your differential that will tell you what fluid it came with from Ford.

 

[Yomie]

Originally posted by Robert
Read page 224 of your Owner's manual. It will tell you you need 5.50-5.80 pints of Motorcraft SAE 75W140 High Performance Synthetic Rear Axle Lubricant. The limited slip also requires 4 ounces of additive friction modifier C8AZ-19B546-A,

ok yeah in my manual it says SAE 80W90, or am i reading the wrong thing? thats the only thing i saw in there under Rear Axle lubricant. and then it has one of them subscript numbers fot the friction modifier

 

[aldive]

I have not, nor will I ever, add anything to my Mobil 1 in the diff.

I have had no problems in my 99 with LS rear.

 

[Yomie]

Well i have access to a lift (the army has some advantages!) I didn't know it was on the diff, but Robert you were right the diff said 75W140 Synthetic oil only. you said it was 5.5 pints, so that would be like 3 bottles right? (i hate conversions) i have the modifier from for for $5. how much does this stuff cost per bottle compared to the 80W90 oil? Thanks for the info guy's i have to chacge out my pinion seal this weekend so ifigured this would be a good time to change my fluid too.

 

[Fred Garvin]

Motorcraft 75W140 synthetic diff lube will run about $17 PER QUART! This is what is recommended.

You'll find many folks on this board who use Amsoil syn or Mobile 1 syn.

 

[Yomie]

DAMN how much is the Mobil 1 75W140 or any other brand that i can find ar Auto zone or something what do thoes ones run?

 

[Fred Garvin]

Mobil 1 syn 80W90 (or so) is about $8 per quart at your local parts store.

 

[JoshC]

i don't know if anyone has tried this i just changed mine out this evening cause i got my locker in and i absolutly hate putting the fluid back it, man it's tough. I think it would be wish to get a hose that would slide over the end of your bottle and stick it in the fill hole cause i just made mess tonight. If you don't want to do that then just fill a bottle about half full and do that until you get it all. I know nobody asked this, i just thought i would throw it in!!

Happy trailes!

 

[JatZilla]

I changed the differential fluid and transmission fluid in my M3 recently..and let me tell you what a HUGE difference a STA-LUBE pump makes, in getting the oil into the case! Piece of cake really, no drip, no mess...just beautiful. The pump costs $4.50 from Pep Boyz. If I didn't have that pump, there's no way to get the fluid in there....

 

[Yomie]

Yeah i thought about that too. My girlfriend went and got me a siphon pump with 1/2 tube, you put one end in the diff, the other end in the bottle with the siphon in the middle and pump away, no mess! She said she paid like $3.00 for it, it is one of them used for getting gas outta tanks and stuff

 

[AgExplorer]

If you're looking for synthetic gear lube, AMSOIL Series 2000 75W-90 is the way to go. Lifetime fill in most applications. This fluid helped Class 8 trucks (the big semis) increase fuel mileage by almost 5% in over the road testing.

But, if you do a lot of towing and/or off-roading, the 75-140 is probably a better choice.

There a several members who have installed this gear lube and reported excellent results. Also, you will only need the friction modifier is the differential clatters.

If you'd like to purchase AMSOIL products, just e-mail me and I'll get them for you wholesale.