Gear swap

[Highroller54]

Hello, I finally signed up since I'm on every other site but so far I'm loving this place! lol. I have a 09 6.4 that I run a black maxx on hd300, 35's in the winter and 37's in the summer. I have 3:55 gears and I really feel they are holding me back. Just doesn't seam to pull like it should but seams to try hard lol. I'm going to get some custom tunes but think gears should be next. Thoughts? Thanks! Chad.

 

[Highroller54]

I don't tow heavy but do have a 30' travel trailer that I tow sometimes. Mostly use it around town. Thinking 4:10's but also thinking a couple more inches and 38's for the summer so maybe 4:30's but then I'm pretty low on winter tires. Looking for expert help lol.

 

[BFT]

I've had 3.73's on 37's on my old CCSB and worked pretty good. I towed a lot as well with it and RPM's were under 2k at around 70. 4.30's would get you to where you need to be

 

[JuststrokeIT]

ive got 4:30s in mine with 37s and I love it, it seems perfectly match.And im sure has really helped save my tranny as long as it has. It pulls hard up top too, I tow quiet a bit with it and its very solid granted mine is on a dually turning 6 tires

 

[SEABEE08FX4]

4:30's are better suited for 37's if you do more city driving than HWY, if you do more HWY driving then 4:10's would be the better choice.

 

[blk350on20s]

I think a 4.10 would be the best choice. Contemplating installing them myself as I run 37s year round but I drive a lot and would hate a big mileage drop

 

[Highroller54]

I think a 4.10 would be the best choice. Contemplating installing them myself as I run 37s year round but I drive a lot and would hate a big mileage drop

I have read every "gear" thread I could find on here and ran some numbers and I think your right. I would consider 4:30's if I didnt run 35's in the winter. I'll order up some 4:10's and poke them in and see how it is. Thanks!!

 

[blk350on20s]

Good deal. Let us know how you like it and the vehicle characteristic changes. Jumping from a 3.55 to a 4.10s a pretty good jump. Should be a fun truck

 

[Fordtrucks]

How did you re configure the speedo?

 

[Highroller54]

I "think" a guy would just lie about your tire size. Lets say 3:55's with stock tires was the same ratio as 37's with 4:10's then you would put your tire size in as stock, you would need to run the numbers to get it bang on.

 

[Jonnydime]

The truck reads the speed from a toner ring on the differential .So changing gears does not affect the speedo.

 

[Highroller54]

that would be correct, good thinking!!

 

[Tree Trimmer]

i cam across this calculator earlier today.

should help you calculate your engine rpm's based on different tire sizes and gear ratio's.

http://completeoffroad.com/p-3351-rpm-tire-height-calculator-page.html

use the "for specific transmission ratio", and our's in 5 gear is .71

 

[Tree Trimmer]

37's, with 4.30's, at 70 mph, in OD, puts you around 1941 rpm's.

 

[fordman2121]

The truck reads the speed from a toner ring on the differential .So changing gears does not affect the speedo.

Actually yes it will. The computer calculates off the toner ring and needs to know the gear ratio. The sct has an option for tire size and gear ratio...atleast mine does.

On another note does the op want to sell the old 3:55 gears out of the back axle?

 

[p8ntballn2]

new gears aren't cheap.. in the same breath, neither is a rebuilt tranny.. i run 37's on 3.73's but don't tow but maybe 10 times a year... usually around 5K lbs... but sometimes around 11K lbs. no issues with my 37's. just run a low HP tune with firm shifts. IDP tow w/ firm shifts FTW zero issues for 35K

 

[ditch_dawg]

On another note does the op want to sell the old 3:55 gears out of the back axle?

Dang beat me to it.

 

[Highroller54]

New gears arn't bad, I dont need to pay labour but I guess a might as well put a true trac in at the same time so it does add up. I guess I could sell the gears but I usally hoard parts lol. They cant be worth much.

 

[Morgan@Midwest Diesel & Auto]

The only thing the new gearing will affect is shifting. You need to change that so it shifts correctly.

The speedo will not change because it uses the same speed sensor gear. Unless you change tire size your speedo does not need calibrated. And even then the tuning will not be that different. You will want a faster shift with the 4.10.

 

[fordman2121]

New gears arn't bad, I dont need to pay labour but I guess a might as well put a true trac in at the same time so it does add up. I guess I could sell the gears but I usally hoard parts lol. They cant be worth much.

Name a price and ill let ya know if I want them. I've been trying to decide if I want 355 or 331 gears so if I can change to 55s fairly cheap it would be worth trying. But if u want to keep them no biggie.