an odd but maybe not so odd question

[smokin150]

ok, after swapping my 4.9 for a 7.3 with a zf5 mated to it im noticing something... im turning almost 2700 at 65mph, now i left the stock ford half ton rear in it cause its too cold to be swapping for my 14bolt full float rear right now, im tryin to figure out the gear ratios with the trans and rear running 31-1050 tires on 15in rims... anyone out there know or have any idea about what i should be turning or what gears i should look into for better hwy speeds but still keepin the torqe for towing?

any help is appriciated

 

[Diesel_brad]

I would guess you have 4:10s in there now, so in a 1/2 ton I would do 3:27 or 3:08

 

[lindstromjd]

Sounds to me like you got pretty close to 4.10 gears from what I'm reading... I may be totally off though.

 

[smokin150]

I would guess you have 4:10s in there now, so in a 1/2 ton I would do 3:27 or 3:08

Sounds to me like you got pretty close to 4.10 gears from what I'm reading... I may be totally off though.

i know the tag in the door says i got the 3.55 gears with the limited slip, it was an old farm wagon haulin a hay trailer around, so the po might have changed it, i know i like my limited slip and the 14bolt i got dont have it, do you know where i can find 3.08 or 3.27 gears with a posi or air locker for the 14 bolt, cause i dont trust the half ton rear to hold up to the torque of the diesel for too much longer

 

[rockbender]

2700 @ 65mph would be about right for 4.10's if you were running a 1:1 final drive (4 speed manual or C6); however, with a ZF5 overdrive it suggests that your gearing is much lower... I'd say 4.56's or lower if your speedo and tach are accurate.

 

[Simp5782]

With 31" tires, 2600 @ 65mph = 4.88 gears. They may have been swapped out or your tach is a little off. 4.56s @ 65 = 2400rpms 4.10s = 2200


I could see someone putting 4.88s behind a inline 6 cause it would pull a house down with 4.10s but with 4.88s itll tow the titanic and ask for more!

 

[smokin150]

With 31" tires, 2600 @ 65mph = 4.88 gears. They may have been swapped out or your tach is a little off. 4.56s @ 65 = 2400rpms 4.10s = 2200


I could see someone putting 4.88s behind a inline 6 cause it would pull a house down with 4.10s but with 4.88s itll tow the titanic and ask for more!

yea, it had a 6banger in it before i did this swap, and it pulled my 10k trailer like it was nothing, so i can see that... thanks for the help

 

[93f250idi]

does it have an 8.8 rear? if it has 4:56s or 4:88s i want em! when you swap rear ends/gears let me know and ill buy your old gears. personally i would go with 3:55s, i hate my 4:10s for a dd

 

[rjjp]

Honestly if it gets used as a half ton, 3.08 would suffice.

 

[MUDKICKR]

if it was me, id keep the 1/2 axles under it. not knowing the year of the truck im only going to guess that it has a 8.8 rear axle. the 8.8 has proven itself over and over again as a very strong and capable rear axle. many 500+ hp mustangs and first gen lightnings run the 8.8 and it holds up fine. also the 8.8 from explorers is a very popular upgrade for jeep Wrangler/Cherokee owners that use there jeeps off-road. the center sections are all the same when it comes to a 8.8, and there is so much aftermarket support for the 8.8, a little money will guarantee you will never break it.
another thing to think about is if you do put the 3/4 axles under it then why didnt you start with a 3/4 to start with?