I have a 2003 F150 with a 5.4 v8. How do I know what ratio to order to upgrade to a posi rear end? Automation with overdrive transmission. 5.5 bed.
Thanks. Ken

 

The sticker on the door jam has a rear code. There should be a tag on the differential cover with the information. Post what you see on those tags and we can tell you.

By the way, you don't need to replace the gears in order to install a traction lock.

 

x2

Plus there is an assortment of diff lockers you can get... you can go OEM or you can extravagant.

 

The door code is under AXLE. It's 2 characters.

 

Attached door sticker to identify my ratio.

 

B6 means your truck came with a 3.73 ratio traction Lock rear diff.

 

So, you already have a "posi".

 

A way to check it to see if it works is lifting both drive wheels off the ground and spin a wheel by hand and the other wheel should spin in the same direction. If it were an open differential the opposite wheel would spin in the opposite direction. Also take a torque wrench and put it on a lug and see how many foot pounds it takes to move the wheels. An open differential you could almost blow on the tire and it would move. I had about 90-100 ft pounds of pre-load on a 4 clutch pack, traction- lok (custom unit), but i think a stock Ford unit is around 40 ft pounds to get one wheel moving.

 

12v power to my rear differential code b6. What does it do or mean?

 

Huh? You don't have electricity going to your rear differential.

 

No 12v power, the electric locker wasn't available in 2003. You have a clutch-type limited slip.