gusguts44

So im planning on changing my differential oil this or next week, but need some input. First my car has 140k miles and i dont think the diff oil has never been changed, would this be a good time to change it? and if i do, should i just remove the drain plug and put the new oil, or should i remove the diff cover, clean all around make a new gasket seal it up, then install the new oil. Im going with royal purple but i dont know what viscosity my car uses.

fordforlife0225

check ur manual or local shop for viscosity. there is no drain plug there is only a fill plug. in order to drain it u have to either suck it out wit a straw like at the doctors office lol we had one at jiffy lube where i worked thats how i changed mine... or pull of the diff cover then put it back on and fill it up till a slow stream runs out the top

SKAR

Pull the diff cover off completely, wipe it out a bit and put it back on, refill as fordforlife said....

Fink

Make sure there is very very very little old gasket material on the mating surfaces between the diff cover and housing.

Azrael

75W-140 is what you want. I'd recommend Motorcraft though, since it is the OEM fluid. Also, it is nearly impossible to change rear end oil without removing the cover. It can be done, but you'd need that straw-like thing. Once the cover is off, scrape down the lip of both the cover and the actual rear end where the old gasket was. Then, when you put everything back together, apply high heat RTV silicone (wait approx. 4-5 mins for it to get REALLY sticky), followed by the gasket. Then, put a layer of RTV on the lip of the cover, and stick everything together. Wait about an hour, and get back on the road.

Hope that's....helpful.

RyansQuick6

I took a scotchbrite pad to my diff and cover to remove the old stuff, get it all off and be very liberal when puting the new stuff on.

RogerDodger1

It it were my car, I would have changed the O.E. fluid in the differential as soon as the car was in the driveway. Failing that, I would have changed it at 50,000. 140,000 is way overdue. To remove accumulated metal particles and clean off the magnet inside the differential, (if so equipped), taking the differential cover off is the only way to do the job right. As for Royal Purple, I will hazard a guess that you haven't seen the gear lube white paper, "A Study of Automotive Gear Lubes", or you wouldn't be selecting that brand. Of the 14 different brands that were subjected to a battery of industry standard tests, RP failed several of the tests and overall tested out as one of the lower performing brands and in the final evaluation came in near dead last, yet they have one of the highest prices compared to the other brands of gear lubes.

Here is the link to the pdf file of the gear lube white paper. There's some darned good information here -

http://www.amsoil.com/lit/g2457.pdf

Here is the link to the online view of the gear lube white paper -

http://https://www.amsoil.com/comparison/gear-lube.aspx

As to the recommended viscosity of gear lube and quantity, it depends on which rear axle your Mustang is equipped with. Below is the link to the Amsoil My Garage look up that will tell you which viscosity Ford recommends and the quantity -

http://www.amsoil.com/products/appli...aspx?zo=349698

Your Mustang's rear axle could have 75W-140 or 80W-90 viscosity gear lube. It's important to use the correct viscosity to avoid wear damage. The look up guide says the differential for the Cobra R Mustang has a Ford recommended viscosity of 75W-140 and the other two differentials, (controlled slip and standard), Ford recommends 80W-90. If your car takes the 80W-90, the hot ticket in a synthetic gear lube is the 75W-90 viscosity and will provide better protection for your...rear-end.

It's also important to use a differential additive if your car is equipped with controlled slip or locking differential, so as to avoid gear-housing chatter noise.

With the eye opening test results of the gear lube white paper, I'd personally strongly advise you to select a different brand of gear lube. Might not make sense to pay more for less protection.

I hope this has been of help.

gusguts44

hey everyone thanks for the replies. I need 3.25 pts of 75w140, and im going with the AMSOIL. I was thinking of making a write-up but not sure yet. Some dude at work told me to spray break cleaner at the differential once the cover is remove to clean all the gunk inside. Once again thanks for the insightful replies.

ShadyNinja

the S197 stangs call for 75w140 the new edge cars can use 75w90


been there done that,
my 2000 v6 stang had 150k when I changed the fluid ( wayyyy over do) I needed carb spray (or brake cleaner) to remove the residue from the old fluid.

take a look
there was a black film that required the help of carb spray to loosen it up

so I thought I would share a few photos.
you can see the parts I have cleaned already









*another thing the Synthetic fluid hardly had a smell, if you have worked with conventional gear lube, you know what I'm talking about*

gusguts44

Hey dude how long did it take you from start to finish.