What kind of fluid should i use ? Its a 98 f 150 4.6,5 speed 4x4 with 3.55 LS . if i use senthic fluid do i need the addative ??

 

You need 75w140 synthetic, and yes you will need the friction modifier if it is not in the brand you buy.

 

My 2000 9.75" 3.55, LS needed two bottles of friction modifier to keep the clutches from chattering on the corners. Suppose to use one, but that year (and other years) some of the LS clutch packs were set up a little too tight. The Ford TSB recommended fix was to replace the clutch pack and remove 0.010" shims to reduce the preload on the clutch pack.

 

Many of the top quality fluids like Amsoil claim you don't need the friction mod, but it's too cheap to not use it just in case. Always used Amsoil Severe Gear 75W140, but never tried it without the mod. You could do one of two things...try it and see what happens and add it later if you need it. Or spend the $6 to begin with and not worry about it at all.

 

If the rear end fulid says you dont need the friction mod and you put it in wont it slip all the time one wheel peel ???

 

No it will be fine.

 

Don't use the modifier if you don't need it. If he stuff you buy claims to have it already, try it like that.

 

how many quarts of 75-140 will it take to fill it up?

 

I think it was 2.6 qts. if I remember correctly. I used my suction gun to fill the rear.

 

I used Royal Purple 75-140 with the motorcraft friction modifier for a bit of good measure even though the RP has it already in it. 2.6 qts sounds about right but your owners manual has that info too.

 

Check out summit racing for PX3 75w140 oil(friction modifier included)...used it on when I changed the rear end fluid and cant beat the price...