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Old 11-02-2017, 03:20 AM   #1
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Differential change from 4.1 to 4.30/4.56

Have to rebuild my differential on E350, 2013 Four Winds 23 footer. So my question is should I consider changing the ratio.

It will cause but how much? Is it worth it?
Extra torque
Higher RPM
Lower gas mileage

Anyone try this?
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Old 11-02-2017, 10:52 AM   #2
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What would you gain by making the change? Faster starts off the line at a stoplight? A much lighter wallet?
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Old 11-02-2017, 11:17 AM   #3
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Do you feel it isn't fast enough in drag races? The V-10 isn't loud enough already that you want to make it run at higher RPM's all the time?

You can't increase the GVWR or the GCWR simply by changing out the diff so it isn't like you'll be able to tow or carry more weight.
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Old 11-02-2017, 11:42 AM   #4
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Gearing your rig down a bit will help with climbing hills, pulling out into traffic, and carrying a full load of "stuff" in your rig.
...But it might hurt your fuel economy a bit...
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Old 11-02-2017, 01:33 PM   #5
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If you could get a 2-speed rear end with the desired gear ratios it might be nice. However, I haven't seen one in quite a while.
Of course, then there would have to be either air or electronic splitter run up to the cockpit so the driver could change rear-end ratio's, and educate the driver, and ....

Probably why they don't offer them!
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Old 11-02-2017, 01:46 PM   #6
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Using a lower gear adds torque. Its like downshifting but not as great. At the same speed the RPM will be slightly higher. This is not about punching it from a stand still. It is about having a little more power available for the rolling hills or towing.

I read a 4.30 is an option for the F450.
Keep in mind we operate at/near maximum limits all the time.

I found these numbers:

55MPH
4.10 gear (stock) - 3rd gear 2586 rpm
4.30 gear - 3rd gear 2712 rpm

70mph
4.10 gear (stock) - 4th gear 2337 rpm
4.30 gear - 4th gear 2451 rpm

70mph
4.10 gear (stock) - 5th gear 1810 rpm
4.30 gear - 5th gear 1898 rpm

I wonder for you that have a E450 and carry a bigger weight load do you have the 4.30 differential?

The effective change to torque is an increase applied to the ground of 4.8%
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Old 11-02-2017, 02:29 PM   #7
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You may be overthinking this a little bit because it's not as black and white as most try to make it.


My Class C was roughly the same size as yours and came with 4.10:1 gears. I had no problems even when crossing the Rockies, or when doing rolling hills. On hills it would occassionally downshift, but that's normal and should be expected. If you gear down so it downshifts less often, you will then pay a price when it does downshift because it'll go to even higher RPMs which may not be necessary. Basically what you gain in one gear you'll lose on the next until speeds make up the difference in RPMs and then it all repeats. As I stated, it's not black and white.


As an engineer I will say that what is black and white is that total gearing also depends on tire size, so your 4.10:1 may actually be similar or even lower than a new F-450 with 4.30:1 gears because their tires are much larger in diameter.
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Old 11-02-2017, 02:38 PM   #8
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Originally Posted by Chance View Post
You may be overthinking this a little bit because it's not as black and white as most try to make it.


My Class C was roughly the same size as yours and came with 4.10:1 gears. I had no problems even when crossing the Rockies, or when doing rolling hills. On hills it would occassionally downshift, but that's normal and should be expected. If you gear down so it downshifts less often, you will then pay a price when it does downshift because it'll go to even higher RPMs which may not be necessary. Basically what you gain in one gear you'll lose on the next until speeds make up the difference in RPMs and then it all repeats. As I stated, it's not black and white.


As an engineer I will say that what is black and white is that total gearing also depends on tire size, so your 4.10:1 may actually be similar or even lower than a new F-450 with 4.30:1 gears because their tires are much larger in diameter.
I did this in a Tacoma and had great results but many others preceded me. The tire size change in the E450 would be important. I get what you say about shift points but it is not that big of a change.

I am looking to see if anyone else has made this change on a motorhome.
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Old 11-02-2017, 03:07 PM   #9
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E-450 and E-350 tires are the same size. I made reference to your comment about the F-450, not E-450. Hope that wasn't a misprint, or that I was too confusing on that -- was typing too fast.


Years ago I think Ford offered 4.10 and 4.30 gears on E-Series (back when I had mine). More recently I think it's either 4.10 or 4.56. Obviously if you are changing the ring and pinion set you have even more choices.


My points about gearing is that spacing between gears plays a major role overall, and that's not usually taken into account as it should be in the bigger picture. I understand you are talking about roughly a 5% change, but how is that going to affect overall performance when gear spacing can be around 50% (more or less) with your 5-speed transmission?


Anyway, I now understand what you want -- hope you get it.
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Old 11-02-2017, 03:17 PM   #10
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Yes I did see it on the F model. I will have to see if it is an option for E models, tire size being checked.

Changing the gear ratio essentially drops the entire driving speed range range in favor of torque. You don't get something for nothing. The trade off is lower max speed, higher rpm for the same speed.

This is the old balance between performance and gas milage. The E350 is multi purpose vehicle, I am just considering tailoring it more for a max load purpose.
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Old 11-02-2017, 03:41 PM   #11
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Since you're looking for "max load capabilities": go for the 4.56:1 gearing.
There seems to be speed-limiting software in the computers anyway! You most likely won't hurt your top-end a bit.
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Old 11-02-2017, 04:08 PM   #12
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You will gain some pulling power at lower speeds, will lose speed at the high end, and will be turning more RPM's all the time, so expect fuel mileage to take a hit. If you have a governor on board, it likely measures engine RPM's, so in that case you will definitely lose hi end speed.
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Old 11-02-2017, 04:21 PM   #13
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The speed limiters that I've seen, have taken their readings from the speedometer. They would allow you to reach the limit in whatever gear you could get there with; and not blow up the engine.
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Old 11-02-2017, 05:16 PM   #14
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Changing rear gear ratio requires changing speedometer calibration otherwise it'll be off proportionally.
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Old 11-02-2017, 05:24 PM   #15
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If you change the tire size: you need to recalibrate.
I'm pretty sure that changing the gearing in the pumpkin doesn't require recalibration...
(But I've been wrong before... )
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Old 11-02-2017, 05:47 PM   #16
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So now my question is: Why do you have to rebuild a 4 year old differential with XXXXX miles on it?
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Old 11-02-2017, 05:57 PM   #17
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A lot depends on what you are doing and where you drive. If you tow anything you are better off with 4.30 or 4.56. Even your MPG may be better. Sure higher RPM's but the motor is also not working as hard so its a trade off. If you do lots of mountians or tow a lot 4.30 and I would go 4.56. I think on my 2016 e450 chassis I have 4.56 but may be 4.30. I tow a 7,000lb boat and it has no problems pulling it anywhere.
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Old 11-02-2017, 06:14 PM   #18
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Originally Posted by Tfryman View Post
So now my question is: Why do you have to rebuild a 4 year old differential with XXXXX miles on it?
I was kind of wondering the same thing...
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Old 11-02-2017, 08:12 PM   #19
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Originally Posted by Tfryman View Post
So now my question is: Why do you have to rebuild a 4 year old differential with XXXXX miles on it?
It has 71,000 miles and was a rental so it never towed anything. We are the second owners. I noticed a rear end noise when accelerating, that was the clue. Drive shaft is tight, universals all tight. The shaft from the diff, pinion gear is not tight. Can move it up and down about 1/4 in. There is also significant backlash before the gears engage the axle, another clue. So the pinion bearings are shot at a minimum. This goofs up the mating of the gears so they will wear wrong so they will need to be changed.
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Old 11-02-2017, 09:07 PM   #20
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Originally Posted by Bob Denman View Post
If you change the tire size: you need to recalibrate.
I'm pretty sure that changing the gearing in the pumpkin doesn't require recalibration...
(But I've been wrong before... )

You may be correct if Ford now measures speed directly off wheels, like by using the ABS sensors or something similar. On older models they took speed off transmission shaft that measured driveshaft speed. In those cases changing the rear gear ratio required speedometer recalibration.
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