So I've been considering gear swaps ever since I've done the X/modded B swap and running 35x12.5 BFG mud terrain km2 on stock 04 18" rims. I've read threw a lot of gear swap threads and it looks like we are down to 4.10's or 4.30's. I will be going the junk yard route for axles. Keeping my stock 3.73's for my f250. I rarely ever push the ex past 80 anymore. I set the cruise every day at 71. I'll kick it up a couple digits if I'm in a rush. My 35's don't like going over 80. I'm going to be purchasing a toy hauler soon that's going to max out or slightly go over my max gvwr. So I have to keep that in mind. So what's everyone's opinion on my setup and what gears. I can get the front and rear 4.30's way cheaper. $700 for front and rear package from a buddy that works at a salvage yard. Still looking for 4.10's.

 

My opinion is with 4:30 and 35 tires you will be at 3400 rpm

Play with the cals and decide where you want to be
https://www.ringpinion.com/calculators/Calc_RPM.aspx

 

How on earth did you get 3400 rpm. Every calculation using both the link you provided as well as the ones I frequent on Wallace show 2052-2100 on 35's and 4.30's at 70. Even running 3rd which is a 1:1, it'll only be spinning 2900 at 70.

The difference between a 4.10 and 4.30 is a whopping 100rpm. Personally, I would go with the 4.30's as they keep you a hair closer to 2100rpm, which is still awfully close to lugging the turbo and causing EGT's to spike like hell while towing. You'll be dropping out of OD a LOT on grades and hills, but as long as you can monitor the EGT's and keep the RPM over 22-2300rpm on grades you should be fine. 4.30's will help with all of this...

My problem with staying at even a 4.30 is that you mentioned the toy hauler is going to be at or barely over the max for the Excursion... With THAT in mind, I would nudge you into the 4.56 or 4.88 camp. Nearly everything drivetrain related in your rig will like you a hell of a lot more, not to mentioned you'll have an easier time hauling all that weight around. RPM's at 70 are 2176 and 2330 respectively.

 

My choices are 4.10 or 4.30. 4.56 and 4.88 can't be had from a salvage yard. There aren't any shops around here that I would trust to change the oil in an axle let alone change the gears. If towing at or near gvwr of the ex is too much for it to handle I'll leave that job to the f250 and buy a 5th wheel instead.

Currently on a somewhat empty truck (500 lbs of tools in the back) I'm pulling 1750-1800 rpms at 70 mph. Towing my 5000 lbs enclosed work trailer it's in and out of o/d if i hit a pebble on the flats.

 

In that case, my pick would be the 4.30's.

 

Before you make the same mistake I did almost 10 years ago, let me point a few things out for you.

The online calculators are sometimes way off and will end up costing you money. The rule according to the mathematical formula says that:

35s = 4.10 gears
37s = 4.30 gears

The formula:
New tire size/Old tire size X desired effective ratio = new, correct gear ratio

In your case:

35/31.6 x 3.73 = 4.13 or 4.10 gear ratio

You can tell yourself you won't take you're truck over 80 mph anymore, but why would you limit yourself with 4.30 gears....? Better yet, What am I talking about?

4.30 gears will actually take your 7.3 out of its power band and make it run out of steam when it's supposed to keep going. I ran 4.30 gears on my 2001 Excursion with 35s on and it had awesome, effortless power at the bottom and first part of the mid range, but ran out of steam during the rest of the mid range and up top. Driving on the freeway, I had to pass someone who was taking her sweet time, so I mashed it, the truck started to take off, but then lost steam, struggled to go farther, then as I let off the pedal, shamefully went back into over drive.

How do I know all this?

https://www.ford-trucks.com/forums/6...y-caved-7.html

From #66-77 everyone kept trying to point me in a different direction. At #77 I had it right though...

Post #102 contains the results of 4.30 gears and what ended up happening.

I still have 4.10 gears in Rudolph and he still effortlessly, tows, passes, and does everything the truck used to do at stock height, just lifted now.

So if I were you based on my past experience, I'd go with 4.10 gears.

 

How do you run out of steam with a 7.3 at hwy speeds?? I've got 35s and 4.10s, I've ran out to 115 mph easy. I can't see a change from 4.10-4.30s making the difference!

Sometimes I wish I had a little lower gear in mine so it wouldn't try to lug so bad at the speed I tow at...

 

I didn't think so either, but it did make a difference.
.

 

That's odd as hell. I hardly noticed the difference between 3.73 and 4.10 in mine.

 

I'm running 4.30 with 35" tires and at 70mph I'm around 2200rpm. Did my first trip back to Oregon since doing the tires and the gears and there is a massive difference! I didn't pop out of overdrive as much as I did before.

I'm very happy with the choice for 4.3 and I don't think putting in 4.10 you will see enough of a difference to make the cash worth it. 4.3 and 35" tires should be a final gear ratio of 4.0.

 

You're also running a 5R110.

We're talking about the 4R100 and while the final drive ratio on both in OD is .71 to 1, how both transmissions get there is very different.

 

For the 4R100, rule of thumb is 4.10's with 35's and 4.30's with 37's. It keeps all the ratio/gear/RPM/speed/math crap closest to what Ford engineered for these single axle rigs.

I have 4.30's on my 37's and they are almost perfectly matched for what came from the factory on 31's and 3.73's.

Those gears would be ok in city driving, but not freeway.

My truck will pull my 10k lb travel trailer with ease on the freeway, and gets up to speed easily, but I'm not sitting on the edge of the RPM band about to fall off the high end of the curve.

A single axle 7.3L truck with 35's don't mix well as a DD with 4.56's or 4.88's, unless it's for specialized service or city driving only.

Stewart

 

Guess I'll be looking for 4.10 axles then.

 

I may or may not have forgotten that my power curve exists everywhere and isn't stock anymore

 

Idk, after pulling heavy with mine this weekend, I would have liked a lower gear than 4.10