First post, new to the site, but been driving ford trucks since I was a kid on my dad's lap. I have a 94 xl f150 2wd auto 300 i6 long bed regular cab with 3.08 gears. I have a 30' travel trailer that weights 5800 dry(no slides or a bunch of extras) I just sold my tow rig, so I'm gonna have to make due with the f150 for a while. I just tow to the local campgrounds, which would be a max of about 25 miles. I figured loaded up for a trip will be in the neighborhood of 7k. I know this weight is pushing beyond the factory tow limits of my truck. I have plans of f250 coil springs, add-a-leafs, helper springs if needed, new shocks, bfg all terrains 235-75-15, hd tranny cooler, and electric fan conversion. I have a 3.73 gear in the box sitting in the basement. My question is should I buy a 4.10 gear? This is not a daily driver(I have a 2014 focus for that). I don't live near the interstate, 50/55 Mph hwy everywhere I go. The truck sucks on gas now, @12 mpg because it is always working to pull all the hills around here with the 3.08. The new tires work out to a 28.9" the factory 225/70/15 are 27.4". Are 4.10 gears to low? Can't find much on this gear with an auto. I'm thinking I will be about 2400 rpm out of od towing, And 1800 in od empty @55mph. Any real life input on 4.10 gears in an automatic with this size tire? I don't need a bunch of info on the 5 speeds, there's tons of that out there. Also don't need to hear about all the laws and crap about towing more than the factory capacity, I don't live in a tree hugger state, and I have driven big rigs over the road for a time period and had plenty of towing experience. My trailer brakes work perfect, and the stability will be fine with my long bed, better than the expedition I use to pull with. How will fuel mileage be driving civilized? The only reason I don't get a f250 is I can't swing it for a couple years, and this truck is exceptionally clean and in great shape. It has everything I want, manual windows and locks, rubber floor, with tilt, a/c, cruise, radio and a long bed. We only camp 3-5 times a year.

 

This will help you with the cruising RPM question: Calculators

The E4OD has ~.71 ratio in OD so the calculations are pretty close.

4.10 gear X 28.9" tires X 55 MPH= ~1850 in OD and 2700 RPM in Drive(3rd). Allow a few hundred RPM more for unlocked converter operation.

Since you already have the 3.73 gears, I would run those......it will transform the truck into something usable for hauling versus driving up and down the highway unloaded.

 

I agree with rla2005. Go with the 3.73 gears.

Over the years of reading about gears here on FTE I note most people stick with either the 3.08 or 3.55's. A few people have used 4.10's on their I6 and they said it was too low for it. If I remember correctly one of them even switched back to the original gears. The I6 doesn't like to rev high and it makes all of it's power low in the rpm band. With what you are doing the 3.73's should do just fine.

 

Thanks guys, was originally thinking of running 31 10.50s and couple of people had said 4.10s, the 235/75s are in the middle between factory size, and there is no 3.91 gear option.

 

There is a 3.90 gear available: Randy's Ring & Pinion 3.90 Ring/Pinion Set

Personally I think you are splitting hairs here. Almost anything is better than the 3.08 gears Ford installed in that axle. Run with the 3.73s you have and be happy.

 

Yes use the 3.73 gears, I suspect your unloaded fuel milage will improve with them too.

 

Thanks everyone. I'm going to take the advise and run the 3.73s I already have, I may do it this weekend if the install kit makes it.

 

Awesome. Let ud know how it works out for you. When I did a 2.73 to 3.73 gear change in my old 1997 Mustang GT it completely transformed the car. After two 1993 Lightnings I do not fear the gear. My recently sold 2004 Excursion V10 came with factory 4.30s. Awesome truck with decent mileage.

 

We're assuming you know what you're doing setting up gears or you're taking it to a shop to be done. It isn't rocket science, but it ain't shade-tree wrenching either. If you just slap it together it'll work... for a while, until the gears die an early death.

 

I believe I could do it myself, I'm pretty handy in the garage, and I've been doing a bunch of reading on the install. But, I'm going to get my father-n-law to help me out setting preload, backlash and checking run out. He's a 42 year heavy equipment mechanic/machinist, a gear head/hot roder and set up race cars for years. It always kills me that no matter what I'm working on, cars, motorcycles, mowers, outboatds, he always knows how to do what needs done. He has set up several.

 

As previously noted there are a few special tools and a thorough understanding of "setting preload, backlash and checking run out." I have done several gear swaps in my home garage with no air tools. All of them went very well with no issues afterwards.

I hope it goes well for you.

 

My father-n-law has the micrometer and magnetic base and the inch pound torque wrench. I was going to make a compainion flange holding tool out of a peice of angle iron I have. Was going to torch a notch in it and drill a couple holes. Is there any other "specialty" tools you know of off hand. I'm sure he has anything I might need at his work.

 

My father-n-law has a 94 lightning. I love that truck. I have driven it quite a bite. They aren't that fast by today's standards, but they were a beast for a stock truck in their day. His only has 81,000 miles on it.

 

Take your old bearings and dremel them out a bit so they slip over the pinion and carrier without needing to be pressed on or off. These are now your set-up bearings. Get your shims figured out, then switch the setup bearings for the new bearings, and you'll save yourself a lot of time.

 

Thanks for the advise, I had read where some people said to do that. But a couple questions, will the old dremeled bearings not effect my measurement vs new bearings? And would I not have to have an extra crush sleeve for that? Or use the old crush sleeve too? I ordered the install kit and bought gear oil yesterday, should be here today hopefully. I may start tearing it down this evening. Was going to pull the bed for easier access since I need a new front fuel pump anyway.