Hi, so i just did a 6" lift kit on my 04 f250 5.4l and put 35's on. i plan on going to 37's but im not 100% sure yet. id like to know what an estimated cost of regearing would be going through a shop, and also if its something someone could do in their driveway (i dont think so but ive never done it). id also like to know what gear ratio i should get, i had 3.73's and 235/85r16 stock and now im at 35x12.5r18 and plan on going to 37x13.5r18's. id like to know what kind of power and mpg increases i might see. i dont care to much about mpgs, as i knew going into this that they would be bad but im interested to hear what it would be like. thanks!

 

Well to start with, you're not going to see any kind of power increase, it will take power to roll thse 37's. MPG will also probably suffer some. Changing ring & pinion gears is not for your driveway nor is it for a someone who has never done it before...... including me.

You need experience, knowledge, dial indicators along with other tools for the r&p set up etc. With your rig I would go with 4.30's of 4.56's if you're not doing a lot of freeway driving. Talk to a few shops in the Boise area and they can tell you what is involved.

If you still want to have it done call this outfit...."STATICZ 2229" (641) 751-8060.... they adverise in Street Rodder and Hot Rod magazines but they also sell parts on ebay. They have new Dana take out r&p sets that go pretty cheap, like $200 or so. They can also tell you other parts you will need as for bearings etc.

I was thinking of changing out the 4.30 gears in my new F350 and talked to 2 shops, one here in So. Utah and the other in Mesquite, Nev. Both shops said it would be an all day job or more for both front and rear and they charge $95 per hour. So I would be looking at $1100-$1200 for labor. Do some research and don't try it yourself, you can ruin a set of gears real quick if it not set up properly.

 

Most of the people you talk to would recommend 4.10 or 4.30 gears for the 5.4 in stock form. Going with something like a 4.56 with tires that big would probably drop you back down to the 3.73 to 4.10 range. There are plenty of gearing calculators out there you can put your data into to come up with the appropriate gearing. I would aim for something in the 4.30 range for the corrected ratio.

 

Your going to be looking at close to 2k to have it done. Like cyncwby said if you don't know what your doing its not a job you can do atleast successfully. As far as ratios go atleast 4.56 but I'd suggest doing 4.88 especially if you are thinking about 37's but even with 35's you'll be better off and pretty close to where a 4.30 factory truck would have been if I rember right it is like 4.39 with 35's and 4.88's but you can check with one of those gear calculators which seems to be the sweet spot for both modular motors in an super duty.

 

i agree i knew i wouldnt see power increase from stock but i mean power increase compared to the 35's i have now on 3.73's. and yea i was kinda figuring i wouldnt be able to just do it in my driveway, but i may not need to take it to a shop because when school starts up this year i could probably do it in my diesel technology class im in. but i was thinking that it wouldnt be cheap either. thanks for the info and i agree i wil probably go 4.56's

 

i was thinking so too. ill probably go 4.56's because i am planning on going with 37's. ill give those ratio calculators a try, thanks.

 

yeah i was thinking 4.36's and damn thats expensive lol and ill have to check those calculators

 

If you're going to be running 37" tires you will want to go with 4.88's. I have 31.5" tires and I regeared with 4.30's and there are times when I almost wish I'd have gone with 4.56's. About 80-90% of our yearly mileage is towing heavy. I may be dealing with different circumstances but with a 37" tall tire I'd still recommend 4.88's.

It will cost around $2000.00 to $2200.00 to have the regear done by a reputable shop. More if you have a Ford dealer do the work and use Ford gears.

 

If you are mechanically inclined there is no reason you can't do it in a driveway. Just take your time and make sure to set it up right. Plenty of write ups online showing how to get it done.

I did the rear end in my Ex in the driveway and the only (barely) special tools I remembered needing were a micrometer (measuring shims), a mag mount dial indicator, and a torque wrench, which I already owned all of them.

 

4.88 is the minimum I'd go with a 37, 5.13 is what will get em moving the easiest

 

This!
If you are going to run 37"s AND want decent performance, then 5.13 is your gear. I run 4.88 with 35"s for an effective 4.39 ratio and that is a very good match for our heavy trucks and these modular motors.

 

Yep, you have a gasser. Gear the **** out of it!!!

If if was diesel, I'd say 4.56 or something with 37s.

 

i want to 4.88's just because im not 100% sure if im wanting to go to 37's or stick with the 35's. i was gonna just stay with 35's because the lift i got was supposed to be a 4" but since i have the 5.4 the heavy spring packs lifted the front like 2 inches more so i had to put rear 4" instead of 2" blocks to make it level(ish). what do you guys think? should i just go 4.88's so i can run either if i want or go with 5.13's for the 37's? i dont do a whole lot of highway driving but when i do i want to be able to pass someone when needed and be able to climb an incline without having to be open throttle 100% of the time like it was for me the other day.

 

After my swap to 4.88s I ran them for over a year with stock sized tires, it towed the then 9,500lb toyhauler like a locomotive and could still comfortably cruise (and pass) on the Interstate. Now with the 35"s and the effective 4.39 ratio it still pulls great, our current TT is 11,000lbs and I can climb most highway grades (here in the East) at or above the speed limit with throttle openings between 60/65%. Granted, my EX has the V-10 with headers and custom tunes but the deeper gears were the single biggest performance mod I've done for it.
Don't be afraid of running deep gearing on these modular motors, they love to rev and make their best power up in the revs. They also tend to be more efficient at those higher revs, our towing MPG improved about 30% with the new gears but I lost about 1 MPG running solo, but some of that lose is due to the 4" lift and 35" tires.
Using this online gear ratio calculator 4Lo.com :: Tire Size Change, New Gear Ratio Calculator I plugged in your 35" tires vs stock 31.5"s with 5.13 gears and it sows an effective 4.62 ratio. That is a very usable number, especially with the 5.4 and big tires, and it won't have you over revving at speed. And if you do go with the 37"s later those gears will net an effective 4.37 ratio, which is still pretty sweet!

 

ive heard that alot! everyone says gears with these modulars motors is one of the biggest performance mods theyve done. thanks for all the good info, you have some good knowledge! i think ill go with 4.88's for sure