3.90 gears- anyone try em' ???

[captain chaos]

So, anyone tried re-gearing on an otherwise stock Expy?
Here’s my situation:
I have a 2000 Expedition 4wd w/ a 4.6 and stock 3.55’s. I use it to haul the family on weekends and pull a variety of trailers ( a 12’ utility, 16’ tandem axle car trailer, a 24’ Travel trailer and occasionally a 14’ alum. fishing boat). I suspect that this truck is geared HOPELESSLY tall for anything other than driving unloaded on flat ground with no wind. A recent family vacation trip, with the boat in tow, has me all but convinced to do a gear swap. Even pulling that lightweight little boat it could not hold OD w/ lockup at highway speeds if there was any kind of elevation change at all. Traveling nearly 1800mi with the truck unable to hold lockup on hills in Wisconsin/Minnesota (we’re not taking Rocky Mts. Here!) was annoying at best. We won’t even talk about how it pulls the TT!

Here’s my thought: I’m eyeing a set of 3.90 gears. By my calculations it should put me at 1830rpm at 60mph in OD/lockup. The engine should be fairly happy there under light load and with small trailers. Locked in 3rd it should be spinning a little under 2600rpm at 60 and that should do for the TT. It should have little trouble holding lockup with the camper under normal conditions in 3rd (I’m in Indiana so hills and excessive winds aren’t common problems). I just feel like 4.10’s would have my hwy RPM a bit too high for mpg’s and 3.73’s just won’t be enough to justify the cost.

My biggest concerns though, are over gas mileage. Unfortunately I am not made of money so MPG’s are a big deal for me. I simply can’t swallow losing 2 or 3mpg (10-15%) in the name of ‘peppiness’. My brother re-geared the 03 F150 he had, which had 33” tires, with 4.56’s and he still swears up and down his mpg actually improved from the re-gear . I do believe my mpg’s may go up a little with the TT in tow simply because the little 4.6 labors SO hard with that thing behind it but I’m concerned with unloaded mileage. Currently I get 19-ish hwy (unloaded) and I’m pretty happy with that for a vehicle of this size. I’d hate for that to drop to 16-ish (which is all I could muster pulling that 14’ boat).

I know the right answer is: get a 5.4 but there are a variety of reason for me to stick with what I have, not the least of which is that it’s paid for.
Anyway, anyone re-geared a basically stock Expy? What were you’re results/ thoughts?

 

[69Hcode]

I think you might be better off spending the money on a tuner and maybe exhaust. Gears are not gonna be cheap with the labor to install them.

With my tuner in the economy mode it takes a lot of throttle to downshift. Torque converter stays locked up most of the time too. Keeps the tranny temps down and helps mileage.

I haven't tried it in towing mode. You can get custom tunes programmed how you want. That's what I did.

 

[captain chaos]

I think you might be better off spending the money on a tuner and maybe exhaust. Gears are not gonna be cheap with the labor to install them.

With my tuner in the economy mode it takes a lot of throttle to downshift. Torque converter stays locked up most of the time too. Keeps the tranny temps down and helps mileage.

I haven't tried it in towing mode. You can get custom tunes programmed how you want. That's what I did.

Labor is a non issue as I'm fully capable of installing them myself. So total cost for a couple gears and related parts is in the neighborhood of $5-600

I really don't believe a tuner will do what I need as the engine simply doesn't make enough power at 1600rpm (60mph locked in top gear) to pull anything other than itself (even that is questionable). Unless a tuner can magically unlock 20-30hp in the bottom 1/3 of the rev range (top of the range maybe, bottom; doubt it) I'm still not going to get what I need for pulling. Besides that, a tuner will undoubtedly require premium fuel which is essentially the same as a 10% drop in mpg as premium is about 10% more costly.
I really thing gears are the way to go. I was just hoping I could find someone with experience to validate my opinion.

 

[Mediamonkey11]

Haven't heard of 3.90's available so my guess is no one will have much of any inupt because if people are gearing up they'd usually head into the 4's. For your desired application that seems like a good gamble as the engine won't be taxed as much so if there would be any decrease in mileage my bet is it wouldn't be more than maybe 1mpg... Can't know for sure though unless ya do it

 

[69Hcode]

Mines a 5.4 so I have more low end to start with. It seems to make a noticeable increase in low end torque. My tune is for 87 octane. I run 86 as that's the cheap stuff at this elevation.

 

[Mediamonkey11]

Even if you try the gears, you can get a tuner that'll make up for your MPG loss form what I hear and from the looks of it still be far under $1k for everything...

 

[Paul2003]

I don't think you'll lose any mileage and if you can install them yourself, do it. Too tall gearing overloads your engine and hurts mileage in all but perfect condition. Try riding a bike in the highest gear, notice how much harder you have to work.

The 4.6 isn't a torquey engine but it does like to rev. I think it will be a very noticeable improvement.

 

[captain chaos]

.....Too tall gearing overloads your engine and hurts mileage in all but perfect condition......

I really think That's where I'm at right now. Mileage is pretty good under perfect conditions (flat road, little or no wind) but tanks off pretty quickly when things go less than ideal or you put ANY additional load on it (trailers).

 

[Madmaxwell87]

Haven't heard of 3.90's available

This is your issue. I don't believe they make 3.90's for the front 8.8 so you're stuck with 3.73 or 4.10. If you tow more than 75% of the time I'd say drop to 4.10s. If you do some daily driving I'd say go down to 3.73. Those should be available in a junkyard too if you'd rather go used/oem.

Another option is a shorter tire which effectively lowers the final gear ratio. But since you're doing the labor (you need a dial gauge to check backlash and be knowledgeable about gear pattern mesh and how to change it with shims on the pinion and/or sides of the differential) the tires would probably cost about the same as the gear change.

You can always start with a intake,exhaust, and tuner to see if it's enough, then if it's not you can go the next step with tires or gears and still have the benefits of those upgrades as the tuner can adjust for all of those changes.

 

[captain chaos]

This is your issue. I don't believe they make 3.90's for the front 8.8 so you're stuck with 3.73 or 4.10. If you tow more than 75% of the time I'd say drop to 4.10s. If you do some daily driving I'd say go down to 3.73. Those should be available in a junkyard too if you'd rather go used/oem.

Another option is a shorter tire which effectively lowers the final gear ratio. But since you're doing the labor (you need a dial gauge to check backlash and be knowledgeable about gear pattern mesh and how to change it with shims on the pinion and/or sides of the differential) the tires would probably cost about the same as the gear change.

You can always start with a intake,exhaust, and tuner to see if it's enough, then if it's not you can go the next step with tires or gears and still have the benefits of those upgrades as the tuner can adjust for all of those changes.

Yeah, a little more digging revealed that for the front; 3.90's are a no-go.

I'll have to rethink my strategy here as 4.10's may be just a tad higher than I want to go (though it ought to pull nice) and I don't think 3.73's will make enough difference to justify the cost.

I may just have to bite the bullet and buy a 5.4 Expy.

 

[MARS]

Hi, don't lose your time and money on 373, go for a 4.10, I have the 5.4 and it had the 3.55 and I made the move to the 4.10 never regretted it, motor isn't laboring anymore fuel Wise it's about the same if not lower, you won't regret it especially if you can do the labor on it

 

[Canadian Expy]

You can do a 4:10 and a little larger tire,
The Edge programmer I put on made a great difference in holding shifts and OD lock-up even pulling a 18" boat and 35" tires. That was before the 4:56 gears.
I'll though I do have a 5.4.