Changing 2018 from 3.31 to 3.73

[bchampion]

I bought my 2018 brand new off the lot back in December 2017 and it did not come with the heavy duty tow package. It's a 4x4 Platinum Max. According to the Ford factory towing specs, the max I can tow with this setup is 6000lbs. Well I would like to be able to tow at least 8000 lbs. The factory HD tow package includes 2-speed Automatic 4wd w/Neutral tow (4x4), Radiator upgrade, Pro Trailer b/u assist, 3.73 limited slip Diff, Trailer Brake controller, Trailer sway control which allows the 4x4 Max to tow 9000lbs. I recently added the trailer brake controller and I asked my dealership if they could change the ration in my rear end to 3.73. They said they couldn't do it and it would void my factory warranty. Well I'm not worried about the warranty and rear end ratios can be changed by any competent mechanic. The upgraded cooling is probably just a larger radiator which I'm sure I could order from Ford parts. The big thing for me is 3.73 rear, I'm not so concerned about the other items in the HD tow package and changing out the rear gears would sure be cheaper than buying a new Expedition.

 

[stamp11127]

May want to research the brakes before making any changes. You're wanting to increase the tow capacity by 50%.

 

[duneslider]

I can't see how changing gears would affect warranty. Anyway, any place that does gears could do a gear swap and probably cheaper. You will need a computer reprogram once the new gears go in and that probably has to be done by the dealer. It is possible that 5star or one of the other programmer companies may be able to make that change. Based on what happened in my Jeep the shift points were WAY off when I regeared. I have heard newer stuff isn't even driveable after a gear change due to errors.

I hate getting all "legal" but in most states DOT won't consider your tow rating higher just because you regeared it, if something were to happen, they would go back to what the factory says. I think in my state there is some process you can go through to get things reassigned but I haven't looked into it.

For me, I am like you, I would regear and see if the cooling needed anything. (Worst case, add a transmission cooler and upgrade the radiator) I haven't used the fancy backup thing at all and probably never will. The stickers don't really fit on my current trailer, if they did, I might try it just for fun but I don't have any issues with backing up trailers.

 

[shane_th_ee]

You're not going to like this. The 3.31 is an open differential. The 3.73 is an electronically controlled, hydraulically actuated limited slip differential, with locking mode. So the difference isn't just a ball of gears. It's a ball of gears, a couple of clutch plates, a hydraulic pump, a wiring harness to connect the pump to the truck's computers, a temperature sensor and some software to control it all. Oh, and the center differential is different, too. I think it'll be cheaper and easier to sell the one you have and buy one with the 3.73.

 

[bchampion]

Well that sucks

 

[Grey ghost]

See if you can locate two center sections from a junk yard but wiring them up would probably be a mess. Hate to say it but trading may be your best bet.
Why not call the guys at 5 star tuning?

 

[osteodoc08]

What are you towing exactly? If it’s a want to tow 8k vs a need to tow 8k.

depending on potential depreciation if selling, may consider buying a used HD to tow with.

 

[Deadman]

Trade it in. Theres 5X more involved than meets the eye.
There's new ABS reluctors needed for the gear change and all the internals of the rear end, a ton of programing that you probably can't get done and then all the headaches of when it doesn't work out and you have $5K stuck into a vehicle that isn't drivable.

 

[byathread]

I thought all the max expeditions have 3.73 rear ends, no?

 

[byathread]

I thought all the max expeditions have 3.73 rear ends, no?

Just looked it up, as you were... [emoji55]

 

[bchampion]

Towing a 7000lb travel trailer occasionally. I won't be traveling all over the US with it. If I really get into the camping seen, I'll purchase and F250 SD PowerStroke so I can tow anything under the sun.

 

[duneslider]

Hold on now, he doesn't need all the other stuff like the limited slip and the transfer case etc. He just wants new gears. As long as someone makes a 3.73 gear ring for the carrier you can slap the gear in there. The only thing that needs to be flashed is the gear ratio, so the computer understands what is going on and can run the correct calculations. On my jeep you just had to have an aftermarket programmer and it would allow you to input the new ratio and all was good. He doesn't need to have the limited slip and 4 low, he just wants a 3.73 ratio which should be doable, he just needs to find out if someone can flash the new ratio. Front and rear ring and pinion install (parts and labor) should be somewhere around 2-3k total plus a flash. I know 5star is adjusting shifting so there is a very good chance they can also adjust the gear selection if needed. It should be easier to do that then mess with shifting.

 

[shane_th_ee]

Hold on now, he doesn't need all the other stuff like the limited slip and the transfer case etc. He just wants new gears. As long as someone makes a 3.73 gear ring for the carrier you can slap the gear in there. The only thing that needs to be flashed is the gear ratio, so the computer understands what is going on and can run the correct calculations. On my jeep you just had to have an aftermarket programmer and it would allow you to input the new ratio and all was good. He doesn't need to have the limited slip and 4 low, he just wants a 3.73 ratio which should be doable, he just needs to find out if someone can flash the new ratio. Front and rear ring and pinion install (parts and labor) should be somewhere around 2-3k total plus a flash. I know 5star is adjusting shifting so there is a very good chance they can also adjust the gear selection if needed. It should be easier to do that then mess with shifting.

What he really wants is an Expedition that will safely and reliably tow 8000lbs. Ford says he needs the 3.73 rear axle. Ford knows that the 3.73 has a higher weight rating than the 3.31. They also know that you can only get the 3.73 rear axle with a different center differential...
Can he safely and reliably tow 8000lbs by swapping just the rear axle ratio? Some other mod to increase the axle weight rating? Does he also need to swap the center differential? Does he need to add the heavy duty radiator? Trailer brake controller? Etc, etc?

 

[duneslider]

What he really wants is an Expedition that will safely and reliably tow 8000lbs. Ford says he needs the 3.73 rear axle. Ford knows that the 3.73 has a higher weight rating than the 3.31. They also know that you can only get the 3.73 rear axle with a different center differential...
Can he safely and reliably tow 8000lbs by swapping just the rear axle ratio? Some other mod to increase the axle weight rating? Does he also need to swap the center differential? Does he need to add the heavy duty radiator? Trailer brake controller? Etc, etc?

Unless we know the carrier split on the differentials I don't know if you can or can't add the 3.73 gears to it. I suspect the carrier for the 3.31 will accept a 3.73 ring.

The safety thing is for him to decide. Whether or not it reliably tows 8k with just a gear change I don't know either but I am pretty curious if you can regear the expedition to 3.73. I really think it is possible.

Let's say someone just wanted lower gearing because they have bigger tires and it feels sluggish. That's why I regeared my jeep. I think it is a valid question to wonder if you can put 3.73 in one that has 3.31's. I think that it is possible. I do not think that you would have to swap the center diff to change gears from 3.31 to 3.73, you might need a new carrier and if you are spending money for a new open carrier then you could throw in a locker at the same time. I have no idea what center diff ford is using in these things, so I don't know what the carrier split is, if it has one. For example, the Dana 30 in the jeep jk's has a split at 3.57 I believe, so if you were unfortunate enough to have 3.21 gearing you can't go past 3.57 without getting a new carrier. If you have 3.73's then you could go up to 5.38 on the carrier. The dana44 in the JK doesn't have a split per say and it will take any ring size up to the 5.38.

 

[Zig10]

This @#$& was so much easier even 20 years ago before there was a sensor for every rotating component in a vehicle. I have to side with the "trade it in crowd", as much as it pains me to do so. By the time you're done finding a gear set that may fit the current carrier, reprogramming, and adding transmission coolers and radiators, you could put that money into another used '18 with the tow package and come out on top.

It sucks, but this is what the automotive industry calls progress.

 

[bchampion]

True, cost me $300 for the new ring and pinion and labor to swap out the 2.79 to a 3.41 in my 8" chunk on my '68 Mustang. WD-40 and a Craftsman wrench will fix just about anything on my '68 Mustang.

 

[bchampion]

I think I'm just going to say screw it and tow with what I got.

 

[duneslider]

It sucks, but this is what the automotive industry calls progress.

I guess it all depends on how you define progress. If easier to work on is the progress you are looking for then that isn't what we are getting. While the 70-80-90's trucks have a lot of nostalgia for me, there is a reason I am driving around in a 2019 expedition and not an 83 suburban and it isn't because the 2019 is easy to upgrade, modify, work on. Both technically would meet the needs I have...

 

[shane_th_ee]

I think I'm just going to say screw it and tow with what I got.

Just make sure you add the trailer brake controller. It's even available as a dealer installed option (dealer install includes the software upgrade to enable it). Or just pick your favorite aftermarket TBC.

 

[scottdm]

Towing a 7000lb travel trailer occasionally. I won't be traveling all over the US with it. If I really get into the camping seen, I'll purchase and F250 SD PowerStroke so I can tow anything under the sun.

You'd be surprised how low the payload capacity's are on some of the optioned up crew cab F250's today. The pin weight on any decent size fifth wheel or gooseneck quickly exceeds the payload on many of the 250's, so may as well jump to a single rear wheel F350.