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 > F250 3.73 to 4.30 axle ratio

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dodge guy

Bartlett IL

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Posted: 06/03/20 06:51pm Link  |  Quote  |  Print  |  Notify Moderator

To those that think that runnng in a lower gear is the same as having a lower ratio, you really don't understand what is going on in a transmission and rear axle? If that was the case then the manuf. would just tell people to tow in "X" gear to tow X amount of weight. Unfortunately it do not work like that. I would much rather spend the money on gears and/or gas than get into a newer diesel!


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jfritz_drfritz

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Posted: 06/09/20 04:13pm Link  |  Quote  |  Print  |  Notify Moderator

dodge guy wrote:

To those that think that runnng in a lower gear is the same as having a lower ratio, you really don't understand what is going on in a transmission and rear axle? If that was the case then the manuf. would just tell people to tow in "X" gear to tow X amount of weight. Unfortunately it do not work like that. I would much rather spend the money on gears and/or gas than get into a newer diesel!

How about explaining the difference to us?

dodge guy

Bartlett IL

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Posted: 06/09/20 05:21pm Link  |  Quote  |  Print  |  Notify Moderator

jfritz_drfritz wrote:

dodge guy wrote:

To those that think that runnng in a lower gear is the same as having a lower ratio, you really don't understand what is going on in a transmission and rear axle? If that was the case then the manuf. would just tell people to tow in "X" gear to tow X amount of weight. Unfortunately it do not work like that. I would much rather spend the money on gears and/or gas than get into a newer diesel!

How about explaining the difference to us?


To make it simple, changing the rear gear ratio to a lower (numerically higher) ratio also effectively changes the ratio of each gear in the transmission. It just like having a longer fulcrum and moving the pivot point. Each gear becomes more efficient. I'm not a teacher so maybe someone's else can explain in depth as a teacher would. I'm just going by common sense thinking! And knowing about physics.

LanceRKeys

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Posted: 06/09/20 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

I agree, it makes every gear more efficient as you put it, but that really only matters when you talk about first gear because you can’t choose a more efficient gear. So if 8th gear is not efficient enough, you could just downshift to 7th. So with 3.73 gears 8th may not be efficient enough, but 7th will be. With 4.30 gears 8th May be efficient enough.

Now why the ratings are different with different gears I don’t know.

All that being said, my next truck will probably have 4.30 gears and a 10 speed.

noteven

Turtle Island

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Posted: 06/09/20 09:19pm Link  |  Quote  |  Print  |  Notify Moderator

noteven wrote:

A 4.30 ratio truck will always have better towing performance than a 3.73 ratio truck all other specs being equal.

The more rpm you can maintain in the driveline ahead of the wheel ends the more power reaches the rims/tires at a given ground speed.


I did explain it.

Grit dog

Black Diamond, WA

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Posted: 06/09/20 11:32pm Link  |  Quote  |  Print  |  Notify Moderator

Last three responses are spot on in their own respects. There are many ways to increase torque multiplication and maximize running in the powerband.
One not mentioned is running the smallest diameter, width and smoothest tread tires possible.
One advantage to gearing down is yes, the furthest downstream you can maintain the low gearing, the more efficient it is. But compared to years past when 2-4 sped transmissions allowed little variable between pulling power and efficiency or high speed travel, now you can have both to a good extent. Enough that re gearing something with a 6-10 speed transmission is of deminishing ROI.
Yes it will help, but will it help $3000 worth? You could buy the same truck with deeper gears for less total expenditure. You could spend twice as much and get triple the re gear increase with forced induction, same gears. Or spend a shade more than that and get diesel.

Not enough juice for the squeeze with re gearing when so many other options are present. Unless you're not worried about $ spent per hp or ft lb gained.


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mtofell1

Oregon

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Posted: 06/10/20 09:42am Link  |  Quote  |  Print  |  Notify Moderator

Lots of guys on the Ram forum I frequent have done it and are happy. However, most recommend going with a much bigger jump than you are thinking of. 3.73 is a common ratio with the Hemi gassers and I was thinking for going to at least 4.56. If sticking with stock tires that is probably good. Guys running larger tires are doing 4.88 or 5.13. There are some good rpm calculators out there so you can see what you'd be running with the new setup.

Cost-wise the average I see is around 2K for both axles. It's varies a lot by area. Just be sure to get a good shop that specializes in differentials. It's not a project for a shade tree mechanic or weekend warrior.

lenr

Indianapolis, IN

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Posted: 06/10/20 11:58am Link  |  Quote  |  Print  |  Notify Moderator

My opinion--yours will vary
OP has a Ford 6R140 transmission with 3.97:1 first gear. It's hard for me to believe that more launch power is needed. The new Ford 10 speed has 4.615:1 for even more launch. There is no doubt that a higher axle ratio will improve the torque and HP in every single gear, but is it worth the cost? Only the OP can decide if it is worth it to him.

dodge guy

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Posted: 06/10/20 12:37pm Link  |  Quote  |  Print  |  Notify Moderator

Having gone from 3.73 to 4.30 myself, it is worth every penny. When I had the Excursion with the V-10 OD was useless when towing. After I could cruise in OD and it would only kick down on the largest of overpasses. It also stopped bogging down on each shift because the gears made the trans work better. I also gained .5 mpg towing.

Grit dog

Black Diamond, WA

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Posted: 06/10/20 10:08pm Link  |  Quote  |  Print  |  Notify Moderator

I got a set of 4.10s I'll trade straight across for someone's 3.42s or 3.73s!
Even on 35s, with no OD, 69mph = 3000rpms!
Does real good burnouts though! Can roast the tries all the way through 3rd gear.

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