Changing 2018 from 3.31 to 3.73

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

OP
OP
B

bchampion

Active Member
Joined
Aug 8, 2006
Posts
28
Reaction score
4
Location
Lafayette, LA
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

Full Access Members
Joined
Mar 20, 2019
Posts
783
Reaction score
372
Location
Utah
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

Full Access Members
Joined
Aug 31, 2017
Posts
868
Reaction score
661
Location
Seattle
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

Full Access Members
Joined
Mar 20, 2019
Posts
783
Reaction score
372
Location
Utah
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

Full Access Members
Joined
May 8, 2019
Posts
215
Reaction score
164
Location
Mid Atlantic
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.
 
OP
OP
B

bchampion

Active Member
Joined
Aug 8, 2006
Posts
28
Reaction score
4
Location
Lafayette, LA
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.
 

duneslider

Full Access Members
Joined
Mar 20, 2019
Posts
783
Reaction score
372
Location
Utah
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

Full Access Members
Joined
Aug 31, 2017
Posts
868
Reaction score
661
Location
Seattle
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

Full Access Members
Joined
Dec 2, 2018
Posts
823
Reaction score
478
Location
Western PA
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.
 
Top