Rear axle fluid

[rkj082000]

I am going to attempt to change out the oil in the rear differential. My owners guide reccomends conventional (dyno) 80W90 Motorcraft axle lube. My question is, is there a reason why they spefically say dyno oil? Are there any problems with using a synthetic gear oil? I have done a search on this and most people say to use a synthetic. If I go with a synthetic, which brand is the best? Amsoil, Mobil 1, or Valvoline? Thanks in advance..

 

[Alec]

I use Ford 85w140? synthetic blend. Dunno why they specifically recommend dino oil for you, but they've always told me to put in this stuff.

 

[SteveVB]

Their 75w140 is a synthethic, and the others are dino, so i think that is why they use the terms in the service manuals.

You can use the synthetics in the axle no problem, If you have the 4.10 rear(which I think was common with the sohc) they speced their synthetic 75w140 in the 4.10 axles though- most of them have a metal tag with the fill requirements on it- mine does.

 

[dogfriend]

In the 97 owners manual, it calls out dino 80w90 for certain axle ratios and syn 75W140 for 3.73 or 4.10 axle ratios or for trucks with the V8 engine. The syn gear lube will perform better, in particular, it should flow much more easily at low temperatures.

The only disadvantage to syn gear lube would be the initial cost, however this is partially offset by the ability to use it for a longer interval between changes.

I don't want to start an oil war by recommending a particular brand. As long as they meet the specifications called for by Ford (I would expect the 3 you mentioned exceed the specs in all areas) any of them should be fine.

 

[rkj082000]

thanks guys, I am going to go with a synthetic. I have seen postings saying that I do not need the friction modifier if I use synthetic, has anyone used both?

 

[dogfriend]

Friction modifier is only needed for limited slip axles. I used Redline gear lube (syn) in my Ranger with a limited slip rear. Redline claimed that friction modifier was not required, so I did not add any. I did notice some 'chatter' when cornering, so later I did add some friction modifier. At least with Redline, there was no problem with adding friction modifier.

 

[rkj082000]

thanks again, leaning towards Amsoil 80w90 w/ motorcaft friction modifier