gear oil

[spederman]

I got 4.10's installed yesterday on my 2002. The shop put in 80w90 premium oil with friction modifier.

But talking to a buddy, per the ford mustang manual, his 2000 says use 80w90 premium with friction modifier, but my 2002 says use 75w140 synthetic . Arent all the rear diffs on 99-04 the exact same? Should i be worried and change the oil to synthetic 75w140?

 

[Kilgore Trout]

Well 80W-90 is the old spec and the new is 75W-140 synth you are correct on that and 75W-140 is what should have been used.

I do not think it will matter and the 75W-140 is pricey so I would say unless the shop is willing to correct it on their dime I would not worry about it.

What is kinda annoying to me is that the diff most likely had a f'n tag on it that CLEARLY SAID what to use and they ignored it.

 

[cw5billwade]

They put 75W 90 in mine which I ran through brake in for around 5K miles than put the 75W 140 both times with modifyer. My guy said first 100 miles not over 45 MPH next 100 miles not over 55 than next 100 not over 65. I have no problems and they run quiet as a mouse.

 

[BannonJr]

I ran 7590 in mine and found drag.

Spoke with ford racing for awhile, and also Amsoil tech. Put in the Amsoil 75w140 its a charm now.