I just bought a set of used 3.73 gears out of another F150. I currently have 3.31 gears (open of course) and have a few questions. The gears that I bought have about as many miles on them as I currently have on my 3.31s so here goes...

What should I look for on the gears as far as wear or damage?
What would be the best Master Install kit to purchase for a 9.75 and how much should I expect to pay?
Is it worth installing these gears or should I just wait and buy some 4.10s like I orginally planned? (I already own the 3.73s though... the price was just too good...)


I plan on putting the 3.73s (or even 4.10s) in with an Eaton-Posi unit. I also have altered my tire size, although I am actually running an insignificantly smaller diameter tire (increasing minimally the gear ratio). I am not looking for labor rates or anything like that I am just curious which master installation kit would be best and the pricing I should look for. I am also a little hesitant about the gears I just bought but the price was also so insignificant that if I decide to scrap them I would not feel too guilty about it...

So what do you think? Is a 3.31 to 3.73 change worth it?

I drive mainly in a very hilly city with a marginal amount of time spent on the freeways. I originally wanted 3.73s then got hung up on 4.10s; but the price in this case swayed me back. I want some performance enhancement without sacrificing too much by way of gas mileage... I know that 3.55 to 3.73 is so slight a change that I would not consider it worth it, but is the difference from 3.31 to 3.73 worth the cost of installation?

Maybe you guys can help me out... I would greatly appreciate your comments, opinions, and views.

Thanks!

EDIT: I also am running a Superchip and with the alteration of both my tire size (I went from 16" wheels to 17" wheels with slightly smaller diameter tires) and gears I will need a reburn of my chip with the speedometer correction... So that will be added in to the cost of this project. In the end will it be worth it?

 

Examine the tooth surfaces for "crowfooting" marks. Crowfooting would indicate that R/P was set-up too close together or had been ran low on lube (initially telling you that hardness on ring & / or pinion was going away).

Look for chips or cracks on gear surfaces. Examine splines for wear on pinion. Check threaded holes in ring gear (make sure no threads are stripped-out or full of old threadlocker). Examine R/P--do all teeth have a nice even, clean, symetrical finish? Teeth may look somewhat gray in color. Take a ball point pen & run it across the teeth & see if you feel any unevenness.

Look for deep pitting on tooth surfaces. Cracks are detrimental! If any cracks on pinion or ring--discard R/P. Chips on leading or trailing edge of gear surfaces can be dressed-up with a die grinder!

I have had excellent luck with lightruck brg. kits (all brg's. are Timken). Lightruck brg. kits come with crush sleeve, new pinion nut, pinion & diff. side shims & new ring gear bolts & new pinion seal. You will need to install new axle seals & OEM Ford or Dana p/n: 43161 friction modifier if You install a L/S.

AS for a L/S: I prefer the Eaton-Posi or the Auburn Pro series.
You might check out: http://www.lightruck.com for a lightruck distributor near where You live. Good luck, Gearmanx17

 

Thanks gearmanx17!

 

Your Welcome!