Ford F-150 Gear Swap (S03E09)

Chris Duke shows you how to a upgrade the gears on a 2005 Ford F-150 from 3.55 to 4.56.

This episode (S03E09) originally aired on MavTV on May 16th, 2010. This version contains the entire show, but with fewer commercials.


Motive Gear
PML, Inc.
Royal Purple
DiabloSport, Inc.

Episode Notes

After 40 episodes of Motorz, we were bound to hit a more complex install. Sure, we’ve had a bunch of installs that have taken 2-3 days to pull off, bloody knuckles and all–but none have required this amount of preparation and tools, attention to detail, and heavy lifting.

My past two trucks had their gears upgraded, but I had a local shop handle it for me. I was always told performing a gear swap was difficult, but that still didn’t stop me from wanting to figure it out so I could do it myself. After consulting with my Technical Director, Jason Gillmore, about the install, and doing a ton of research on my own, we figured out which products and tools we needed.

There are many reasons to do a gear swap, but in our case it has been needed since the F-150 was lifted 6″ and 35″ tires were added back in S01E04. You see, when you lift a heavy truck like this and add on the extra weight of huge wheels and tires, the truck isn’t as quick off the line. It loses low-end torque because there’s much more mass for the engine to push forward.

That’s where new gears come in handy. In our case we went from a stock 3.55 gear ratio to 4.56, which means there are more teeth in the ring gear. As a result, the gears spin faster which helps when you punch the pedal from a stop. The downside is that your RPMs increase, which is why you need to get a programmer that connects to your OBD-II port and tells your vehicle’s computer about the gear ratio change. If you don’t do this, your speedometer will report a much faster speed than you’re actually going. You have to fix this problem immediately, as the side-effect to this is that your odometer will also increase faster and put more miles on your vehicle than you’ve actually driven!

As for the install, there’s too much to document here, so just watch the video! You are definitely going to need air tools for this job. We forgot to cover this fact in the tools segment at the top of the show, but that’s why we have this notes section here. You’ll need an impact gun for the pinion nut, as well as a chisel tool to remove the inner and outer bearing races. We tried using hand tools and it just wasn’t possible. Plus, having air tools will help you get the job done more quickly and this is a long install.

I had the help of three other people (including my camera guy, Jason) and it still took us the equivalent of two full days. So, if you take your vehicle to a shop and are shocked at the labor cost of around $1,000 you now know why–it’s a lot of work! But you can save yourself a lot of cash by doing it yourself… just do your research and take your time. It also helps to have someone around that’s done it before because you will have a lot of questions if you try to do it yourself. This install scores a 9/10 on the difficulty scale, but mainly due to the amount of labor. It’s not incredibly difficult, but there are a few parts that require some skill.

Before we decided to film this episode I couldn’t find anyone that had documented a step-by-step gear swap online on video, from start to finish. And those “how-to’s” that I found online in text format were missing a lot of details and covered the install more as an overview. Our goal for this episode of Motorz was to show each step as best we could within the confines of a half-hour TV show format. I really think we pulled it off, and I think this is our best episode to date. Please post your comments in the area below. We’d love to hear what you think!

Thanks a bunch to all the manufacturers who supplied products for this episode. Motive Gear supplied the ring and pinion gears, plus the kit which included extra bearings, RTV, paint, races, and more. Royal Purple supplied the 75W-140 gear oil, PML, Inc. sent us an incredibly cool rear differential cover (as well as a transmission pan which we’ll show you how to install in a later episode), and DiabloSport, Inc. supplied us with their awesome touchscreen Trinity programmer so we could tell our F-150’s computer about the change in gears (as well as our tire size).

This installation also wouldn’t have been possible without the help of my crew, including Jason, Jason and Andrea, not to mention the patience of my family. So thanks to everyone for your help. I’m very proud of this episode, and it was a huge learning experience for us all. I hope that everyone who watches this episode not only learns how to do a gear swap, but also becomes a little bit more educated about how rear differential gears work!

Note: According to Royal Purple, the friction modifier is not required. All of the necessary additives and then some are already in there! While it didn’t hurt to add it, that step was not necessary.

Product Information

For more information, just click the products on the right!


This episode features music from COLDWEST. “Snakeskinner”, “Ignition”, and a custom song for the Motorz Intro.

Other Information

If you’re interested in a great overview of how gears and limited slip works, I highly recommend watching this old General Motorz video. It was produced by Jam Handy Pictures in the 1930s but still applies to today’s rear differentials. It’s a must-watch!


  1. how much more work would the front diff be on my 2006 f150? how come you talk about installing motive gear’s 4.56 gear when theres only a 4.57 listed on their website?
    ive got a 4×4 supercab 2006 f150, would this have the same 9 inch rearend with limited slip?

    im also considering 34.5 inch tires and wonder if the 4.56 gears will bring the rpms exactly[i mean within about 3%] back to stock or higher/lower?

  2. i have a 1998 f150. its good on the highway but doesnt haul well. what gear do you recommend i change to make if more compatible for hauling?

  3. GREAT SHOW!!! i love both the mustang and f150 builds cause i have both vehicles. I have some questions about the gears. Will you need the friction modifier if you go with an ARB air locker? also i am running a 5.4 supercharged f150 prerunner setup and want to go fast, should i go with a 4.56 ring like you or should i go higher? My truck is only off road not highway.. so i the faster the better. thanks again for a great show.

  4. just thinking about my last comment. do you think it would be suggested to swap out my axle to a dana 40 instead of the factory f150 dif? I only ask because i am doing an ARB airlocker and gears on a 500+ HP 06 5.4 f150. thanks again

  5. By the way, Chris, is this the biggest gear ratio I could get for my truck if I chose to get myself an 8 inch suspension lift and 36 inch tires?

  6. I have an 05 f150 with 5.4 n 3.73 ls diferential n I get horrible mpg what kind of gears can I switch for better mpg I don’t town at all thanks

  7. Never understood why Ford quit putting the 9-inch under their vehicles. If the 9-inch is strong enough for the Nascar vehicles with 800+ HP(yes, all stock cars have a Ford rearends whether Chevy, Toyota, or Dodge) why wouldn’t they handle street horsepower? Besides, you can pull the chunk and wouldn’t need to lay in the dirt to change a ring and pinion! Later, RT.

  8. Didn’t see a center spring for the LSD clutches. Is this a limited slip or open diff? Why use the additive on an open diff?

  9. OK i’m just curious why you would need to spend the extra $40 on a new inner pinion bearing to destroy rather than just use the original bearing? You didn’t buy a new outer bearing so why buy a new inner bearing? Just a bit confused here if you could please explain that’d be much appreciated

  10. I have an 05 f150 and my pinion seal has gone bad is this the way to change it as in can I do this in my drive in a day ?

  11. Love this video great editing these guys are not using Windows Movie Maker!! Come on Brits we need to make more How to videos like this Americans do it really good thumbs up !!

  12. BOY….Ford sure went backwards when they dropped the old style with the drop out ubit…so you could drop it out and take it to the bench to work on…much simpler….is this a way to get the vehicle BACK to the dealer or repair shop????

  13. Hey, I’ve got a very good good question here. What differential should I get in my 1989 f150 302 lwb? It has 3.55 gear ratio in it but its so slow at first but goin at about 75mph I can just tap on the gas alittle bit and im already at like 90mph but it takes me like 10 seconds to get to 60mph what gear ratio should I get for it.

  14. I am currently changing my differential and gears on my Mustang from a 327 to 373. When installing the differential they provided shims to achieve the 8 to 12 thousand end play. After you find the exact shim spacing between the differential and the axle tubes. The tech from Ford Racing said I would then order the correct shim for each side from Ford. Is this necessary or could I just use the shims that I used to get the correct end play

  15. Chris, that was a excellent informative video. In fact I would say that your video is heads above similar repair and upgrade video’s that sadly shows a unknowledgable wannabe talking about how to do a repair or upgrade and not having the ability to do the actual work. Keep making video’s, I’ll watch’em so I can learn to do my repairs right the first time.

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