What is Ford's recommendation as to when to change the differential fluid? I thought it was some high number like 50k or 75k since its synthetic, but I serviced mine the other day with just shy of 38k and it was low and definitely due. Looked like used diesel oil coming out.

Also, I thought the manual trans fluid is good for a long time (75k+) but I also replaced that. Had started turning a dirty purple-red color..

Amsoil in both

 

What do you mean by "low" did you have a leak or something?

 

Ford's recommendation is actually "lifetime" fluid. Unless the rear axle is submerged under water, you should never have to change it. No matter how many miles on the standard fluid, it's going to look and smell like crap.

I called BS on that too, and changed it anyway. I would never run over 100,000 miles without changing it, no matter what Ford says. Use a good quality 75W-140 and change it (don't forget the friction modifier). Obviously, I use all Amsoil products in mine.

This reminds me of other car brands saying their transmission fluid is a "lifetime" fill, and never needs to be changed. The owners who changed the fluid anyway still have an operational OEM transmission. Those who didn't change their fluid ended up needing a rebuild.

 

Changed out the transmission and rear end to Amsoil fluids at 5K on my Snake...there was a lot of goo in the rear from the gear wear in...
Did the same change out in my 06 GT at 15K...same goo in the rear...the wear-in does create some metal...

 

I don't have our computer system in my hands from work, but I believe that the recommendation off the top of my head for the rear diff. is every 15k. As for the manual transmission, that one is every 30k miles.

And I would never buy into a "lifetime" thing either. Fluids are going to break down over time, no matter what they are. And anything that is a fluid that has to deal with your drivetrain is going to be under some pretty heavy stress unless you just drive on only highways for 45+ minutes at a time before parking again.

 

Went to Advanced Auto Parts who looked up my car (2005 Mustang GT) and sold me 75W-90 rear end oil. Checked my owners manual and the oil recommended is 75W-140. Will I have a problem if I use the 75W-90 oil?

waterboy

 

You better take the 75W-90 back and get the proper oil. Tons of difference between those 2.

 

100K for the diff.
I wouldnt go that long.
I changed mine out at 30K something
when the rear axle bearings got replaced.
I went with Royal Purple 75W-140.

Um, yes.
Thats why there are different weights and specs involved.

Some mustangs left the factory with low fluid.
It should be up to the fill cap and not an inch
below like the service manual states.
Mine was low and I think thats why the
axle bearings went south at 30K miles.

 

With clutch packs in the differential it's best to change the fluid every now and then. Don't forget to add some friction modifer if your car has a factory limited slip. However, some gear oils, such as Royal Purple Max Gear already have friction modifier in its formulation.

 

Good to see my thread got bumped up I checked my differential and manual transmission again recently and they both looked perfect. Will probably do 50k on both of them since I used Amsoil products