Looking for some advice on a rear axle rebuild. My 2001 F-150 4x4 with 5.4 has the 9.75" rear axle. It currently has the factory 3:55 with limited slip. I regularly tow a 6,500 lb travel trailer. Truck is NOT a daily driver. It tows my trailer quite well, but longer inclines do give it some trouble. I'm looking to upgrade the gears for more hill pulling power. I have 32" tires. Looking at 4:10 gears. Would 4:56 be too much with 32" tires? Also looking on opinions on different gear brands. Who makes a reliable gear set? And yes, I do realize I need to change out the front axle as well with a reverse cut 8.8" set.. Any opinions and/or real life experiences with a gear change would be appreciated! Thanks.

 

Just a thought....is the 6500lb weight just the travel trailer ( dry weight)? ( not including camping gear, dishes, water & what not) Or does that include everything?

If that is dry weight then you can add nearly 1000 lbs to it, maybe another 500-800lbs more if ya got larger family and all their clothes, toys, bikes and what not. Point is it adds up fast.

Considering that it is not a daily driver and if it primary purpose is to tow your travel trailer. I'd lean more to the 4:56. I mean, your not driving it daily and when towing your MPG's are in the dumpster anyway. why not give yourself a little more gumph. Even if ya drive around a bit without the trailer, you probably wouldn't see the loss of MPGs until ya got'er out on the interstate for a extended period of time.

The 4:10 gear will help too, just kinda depends on how heavy your travel trailer is when fully stocked.

 

You should also get a programmer with custom towing tunes. You will need it anyway to correct the speedometer/odometer after the gear change.

 

Scaled the truck and trailer last trip fully loaded to camp. Truck GVW was about 6,200 lbs. and GCW was 12,000 lbs. So yeah, definately towing at the upper limits for the '01 F-150. I do have an SCT tuner with a custom towing tune which helps a lot with transmission shifts. Also did the Super Duty (from a 2004 V-10) transmission cooler mod, which is awesome! The 14 row stacked cooler is massive compared to my stock cooler. My trans temps dropped about 40-50f ! Used to go over 200f during hard climbs, now barely hits 170f on tough inclines and a flat land temp of about 160f cruising on highway at 65mph and about 85f ambient temp. I'm leaning towards 4:56 since the truck is only really used for towing and hauling. Already gets 7.5mpg while towing my camper so how much worse could the mpg be! Lol.

 

Just wanted to give everyone an update.. I finally re-geared my 2001 F-150 last month. I went with 4:10 ratio and replaced the original Traction-Lok unit in the rear with a Detroit True-Trac. Wow, what a difference! The overall driveability of the truck is much improved. Hardly have to press the accelerator much at all to accelerate up to speed. When on the highway, now can climb moderate grades without downshifting out of OD (not towing of course). Towing feels improved as well. We bought a new travel trailer that weighs about 7,200 lbs. loaded which is about 1,000 lbs. heavier than our old trailer. The truck actually pulls the new one a little easier! And much to my amazement, my towing gas mileage went UP about 1 mpg! Regular driving also went UP about .5 mpg. And yes, I did program my tuner with the new gear ratio. I have no idea why Ford didn't make this gear set a factory option back in 2001. SO much better then the old 3.55's!

 

corporate average fuel economy CAFE is why all vehicles are geared so high.