my 60k maintanance is coming up. im gonna do my fuel filter, t case fluid, trans filter, and probably my diffs.

the diffs dont have an interval on them. the manual says for the rear synthetic 75-140. ill probably get mobil 1 for that. then the front just says premium rear axle fluid 80-90. my jeep was like this, took syn gear oil in the rear, and non syn in the front.

should i just put 75-140 syn mobil 1 in the front and rear? or do the 75-90 or whatever it is synthetic mobil 1 in the front? or just go with normal old 80-90 in the front?

also, i need to get the ford friction modifier. it says to do 4 oz of the ford stuff in the rear, its best to get this from ford right? the stuff i sell at advance is 7 oz of trans x additive for limited slips, but thats too much isnt it?

also, i did the trans filter and fluid at 50, cause it had never been done, im gonna do it again at 60k so i can get it onboard my 30k intervals. it was decently dirty at 50k, theres no harm in doing it again is there? what is the torque spec on those bolts, they werent on there pretty tight.

thanks guys.

edit: sorry

this is a 07 lariat 5.4 with a RP 8.8 front and 9.75 rear axle with the 3.73 limited slip.

 

I would put synthetic 75W-90 in the front. That is an acceptable substitute for 80W-90 conventional. 75W-140 is too heavy.

Yes, get the modifier from Ford. It's not that expensive.

 

or you can get royal purple 75w140 syn at pep boys and it already has the modifier in it.

 

is it the right ratio?

 

I'd rather have the Ford-specific modifier in there. Maybe I'm just too picky.

 

i kept ford modifier and went amsoil 75-140 for rear its cheaper than mobil one and better from what ive heard. ams 80-90 front

 

is there any decent brand i can get online for a better price than the mobil 1? anyone used the wallmart syn gear oil or is that not a good idea?

 

i am in the same boat as u brother - I am looking at Lucas on amazon
http://www.amazon.com/Lucas-10121-75...=pd_sbs_auto_2

 

so then this

http://www.amazon.com/Lucas-10121-75...=pd_sbs_auto_2

for the rear and this

http://www.amazon.com/Lucas-10047-75...=pd_sim_auto_2

for the front?

 

Walmart syn is fine, it meets specs.

 

so general consensus for the front is that full syn 75-90 is fine for the front, and 75-140 is good for the rear?

 

thats what I am going with ... never heard anything bad about lucas oil

 

I'm about to change out the diff fluid on my FX4 as well. I was wondering what the volumes were that I should be filling. Does anybody have that off hand?

 

capacity for them? if your truck has a 8.8 front (it should) and a 9.75 rear, (vs an 8.8 rear, or a 10.25 rear) then the front takes 1.85 quarts and the rear takes 2.75 quarts. and remember if you have a limited slip (axle code on door sticker starts with a letter not a number) then use 4 oz of ford friction modifier first, then fill it with gear oil.

 

Why would the fluids be different in the front and rear differentials?

Would the friction modifier (4 oz.) volumes be the same even though the total fluid volumes are different?

weird for both items...