Hello everyone, Well it's about time to change the rear end fluid in my 1998 F-150. It has a 3.55 geared traction lock rear end. I want to go synthetic. Which one will work best with my truck. Mobil 1 or Royal Purple?

 

i used amsoil 90-140

i wouldnt use ANYTHING royal purple makes

 

Um ... Ford specs 75w-140.

OP: RP, M1, Motorcraft, Amsoil, Castrol Syntec, etc - any one will do. I believe you need to add a small amount (4 oz) of Motorcraft XL-3 Friction Modifier or equivalent, from Amsoil for example), as well - that's what the manual clearly specifies for 8.8 & 9.75 Traction Loks ...

BTW - I could NOT find a 90w-140 Amsoil gear lube: http://www.lubes-n-filters.com/synth...gear-lube.html

Got a linky?

 

There's not one. It's 75W140 Severe Gear...and the Amsoil is arguably the best gear oil available!! Amsoil also has the friction mod additive as mentioned. One stop shopping.

 

I use RP 75-140 but also use the friction modifier Ford sells as well. Won't hurt for added protection. Almost positive all are synthetic. Use whatever you can get your hands on, changing it with anything is better than not changing it like most people do.

 

I just did mine. I used Redline 75-140, with two bottles of modifier. The techs at teh local dealer reccomendd two botlles on modifier. I have been using Redline for years in a wide variety of vehicles, with zero issues.

 

Whatever 75W140 full synthetic you can get the cheapest, along with a bottle of friction modifier from the Ford dealer.

 

Hey everyone, Thanks for all the great info. I have a couple of other questions. How many quarts of rear end fluid will I need & what is the best way to fill the rear end? Thanks. Chief Mike.

 

That information should be in your owners manual. Which engine do you have? That information will determine axle size.

 

Easiest way to fill it is with a hand suction gun. Suck the fluid out of the bottle and pump it into the axle.

 

This is a pretty true statement. Ford synthetic does a good job, if Ford is going to state the rear end doesn't need servicing.

Oil opinions are like rear ends, everyone has one. Of course Redline rules.

 

I used valvoline because its the only 75w140 my local napa stocks.