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i have a 91 f150 4x4 with a 351. i want to go up to 38" mudd tires and i am concerned about what gears or rear end replacement i should use. should i go 8 or 10" up and what about my transmission? i know i'm gonna have to make alot of changes i just don't know what changes i should make?
If you plan on 4 wheeling hard with 38s, your 1/2 ton stock axles will be the weak link. If its mostly street and mild wheelin you may get by. 4.88 gears will be about right for 38s. 38s is alot of tire for TTB front end. Im not saying you cant do it, just be prepared to change a few parts in the front end when wheeled hard. I broke a few axles running 35s. Replaced with junkyard parts and kept on going. Good Luck.
While it would fit, and could be done, the AOD was not put behind the 351 in these trucks. C6, then E4OD later on. Either tranny is fine. If you have OD, it's the E4OD, if not, it's the C6.
this is a hard question becasue you didnt specify the type of use this vehicle will see. but if i was you this would be the route i would take.
do an SAS up front with a Dana 60 and run 5.13 gears.
rear would be a D60 or 14bolt either is up to you running 5.13's as well.
install the largest tranny cooler you can find along with a remote tranny filter and tranny temp gauge.this is how you keep the auto happy and alive.
the sas will gain you the needed lift height for sure. check out fullsizebronco.com for a huge forum specific to SAS installs.
since you have an OD tranny the gears i mentioned will be just right. i currently run 4.88's with 35's.
If your just worried about tires clearing go 6" lift with a 3 inch body. Your drivetrain will thank you and you won't believe how much easier that two inch difference makes on cost and hours configuring angles.