I have 315 70 17s coming in tomorrow. I plan on running them on my 2wd 04 5.4L Screw with 3.55 open gears for about a month before I upgrade my gears. Anybody know how much approx. it would cost to upgrade to 4.56/4.88 gears in the rear, with a detroit locker? How much damage are we talking on my truck, running 35s without lower gears? I'm new to the "modification" world, and reading as much as I can. Seems like no matter how much a person can read, the best knowledge comes from people who've actually been there and done it!

EDIT: Looking at parts online, how do I know if I have a 8.8 or 9.75" Rear end?

 

You have a Ford 9.75 rear end with 1.37" diameter, 34-spline axles. As for prices, shop around... but 4 Wheel Parts has deals for a new gear set, master overhaul kit, and choice of lockers. Check out there website, 4wheelparts.com, they may have it on there, I saw it in 4 Wheel and Off Road Magazine...

 

Here is a link that might help you out abit...

http://www.eatonperformance.com/PDFs...guide20107.pdf

 

if you want to go a cheaper rout, i have a factory trac lock LS out of my 9.75 with 40K miles i will sell you for $100 plus shipping, just giving you a diffrent option.