family wagon

I have looked and cant find anything about how to find out if the rear end gears have been changed....Is there a easy way to see if they have or do I have to pull the rear end cover off ? I want to order and programmer with a custom tune and fig I prob should find out what I have first ! Thanks for the help

Thunderslide

raise rear of truck off ground. support with jack stands. rotate tire 1 rev, count drive shaft revs. should see 3.55 revs of drive shaft to one rev of tire. or 3.37 revs. a rear end ratio is x.xx to 1 so count the shaft turns for 1 tire turn. that's the ratio. now there will be come guess work between 3.55 and 3.75 but 1/4 turn of shaft should be detectable.

family wagon

Thanks I have heard of that but wasnt sure if that really worked...

f150cwcw

If you take some white chalk and mark the tire, drive shaft and where the "U" joint hooks to the differencial, this might help you identify how between 3.55 and 3.73.

family wagon

I know on my door tag it says that the truck comes with 3.73 but I have 325X65XR20 so I'm not sure if the pervious onwer regeared the rear end. Since I have bigger tires that is going to throw off the rotation so how would I know if I still have the 3.73s or something diff. Hell what is stock size tire for a 06 f150 4X4

Thunderslide

Tire size has NOTHING to do with the ratio of the rearend. one rev is one rev is one rev. tire size affects the distance traveled with that one rev. the ratio never changes per tire size change. This is the ONLY way to confirm without opening the cover and counting teeth or finding documentation of what it was changed to... If you bought it used you can't know it was not changed. my 06 XLT 5.4L 4X4 3.73:1 came with 255/70/17

family wagon

Thanks for the info....I'm new to all the truck stuff so sorry for all the question !

Thunderslide

no problem at all!!! hope you can figure it out. it is really simple if you have a jack and stands. mark the tire and drive shaft. OH BLOCK the front wheels so it can't roll.

family wagon

Damn I prob should put blocks up front but what's the fun in that LOL jk

Thunderslide

Sometimes the obvious escapes people. (see Sig line)