Diff Gear change - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 5 (permalink) Old 03-08-2011, 07:25 PM Thread Starter
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Diff Gear change

I posted this elsewhere but I would like to see what this crowd has to say....

I have a 6 inch lift with 35's and 3.73 gears. This puts me down in gearing from stock. I now have the equivilant of 3.55 gears (approx). I am pulling a lot and my towing milage and power are way off. I am planning on regearing this weekend but I want some opinions on how far to go. (if your answer is all the way I'll take care of that later and in another way)

My current RPM is shown below with the 3.73. I multiplied the difference in gears to show the different RPM at different speeds. My RPM data is from driving and gps readings off the stock tach so I may be off a little thate but it will be close. I pull a lot and usually travel at 65 on the freeway although 70 has been seen. My empty speeds are not much different.

Gear 3.73 4.1 4.56
55 1250 1375 1525
60 1400 1540 1708
65 1500 1650 1830
70 1625 1787 1982

I pull a 16 ft. work trailer that is about 4-5k most of the time and my toyhauler is a right at 10K when loaded. I don't usually take distance trips empty (that's what the crown vic is for) but I may occasionally depending on weather and load needs.

My question is...
With 4.30 gears not an option (I have looked and asked) 4.10 would put me back to basically stock RPM's. Would 4.56 be too far? (I know...another set up)?

Ideas, experience and opinions welcome.


2008 2500 HD Megacab 4X4 CTD, 6 speed Auto, Mineral Gray, SRW #143 - 28TB Tahoe Toy Hauler
Utility quads, 2 kids and one awesome (and patient) wife. Priorities not listed in order of importance

Last edited by rXr; 03-08-2011 at 07:38 PM.
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post #2 of 5 (permalink) Old 03-09-2011, 12:52 AM
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How heavy are you towing and is it flat land or mountain towing. I am happy with the performance towing 12,000lbs in the mountains with stock 3.73 gears. Looks like 4.1 would put you back close to 3.73 but again how heavy?

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post #3 of 5 (permalink) Old 03-09-2011, 01:16 AM
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I would do the 4:56 My truck with 4:10 stock runs right where you will be at 70 mph.
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post #4 of 5 (permalink) Old 03-09-2011, 01:51 AM
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Why not simply run in 5th gear when towing????

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post #5 of 5 (permalink) Old 03-09-2011, 05:41 AM Thread Starter
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Any place in the drive train that you are behind the power curve is a place with excess preasure. Down shifting is an option but it's like a bike that has the chain on on the rear tire on the smallest gear and instead of changing the rear gear we make a smaller font (pedal crank) gear which does nothing to take the strain off the system. It takes a lot of presure off the sysem (and uses less energy ie the power curve) to regear the rear.

I posted above that I pull 5k plus on a regular basis and tow about 3000 miles a year with a 10K toy hauler. I also pull a dozen times a year or so a rented 14k dump trailer locally.

Changing to 4.56 will be close to the equivilant of 4.10 with my current lift and tires.

I'm currently feeling like 4.56 is my best option but I'm still interested in ideas and opintions.


2008 2500 HD Megacab 4X4 CTD, 6 speed Auto, Mineral Gray, SRW #143 - 28TB Tahoe Toy Hauler
Utility quads, 2 kids and one awesome (and patient) wife. Priorities not listed in order of importance

Last edited by rXr; 03-09-2011 at 05:45 AM.
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