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Old 08-17-2020, 11:18 AM   #11
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If you do decide to regear, go at least to 4.30 gears. That engine does better with higher rpm, especially with the weight you are hauling, and your whole drivetrain will thank you.
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Old 08-18-2020, 09:41 AM   #12
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Re-gearing from 3.73 to 4.10?

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Originally Posted by tedujam View Post
Thanks for all the feedback. I'm now looking at BFG Mud Terrain 255/75R17s or Nitto Terra Grappler 285/70R17s. Neither of them are bigger than 32.7 inches, so it sounds like I should just stick with my 3.73 gearing.

And why the size differences between the two tires?
Theres no way to give you gearing advice without knowing what size tires youll ultimately end up with, so Id finalize that before doing anything else.
Most SMB 4X4 conversions run 285s, and depends what engine when it comes to gearing, some of us have gone bigger to 315s, but it might take some other modifications to get there, including gearing. My 7.3 started on 285s from SMB with 4:10, Im now running 315s with 4:56, but Im also towing.
So it really all depends, but if youve got a ujor 4X4, they usually are setup with a pretty good lift, I think youd want some tires to fill in the wells at least a little bit, 285s at the minimum.
Got a pic of your rig to share?
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Old 08-19-2020, 02:24 PM   #13
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And why the size differences between the two tires?
Theres no way to give you gearing advice without knowing what size tires youll ultimately end up with, so Id finalize that before doing anything else.
Most SMB 4X4 conversions run 285s, and depends what engine when it comes to gearing, some of us have gone bigger to 315s, but it might take some other modifications to get there, including gearing. My 7.3 started on 285s from SMB with 4:10, Im now running 315s with 4:56, but Im also towing.
So it really all depends, but if youve got a ujor 4X4, they usually are setup with a pretty good lift, I think youd want some tires to fill in the wells at least a little bit, 285s at the minimum.
Got a pic of your rig to share?
The tire size difference is only about 1/2 inch. I didn't pick those sizes specifically, those are just the best 2 used/nearly new tire deals near me right now. I'd normally go with whatever new tire deal Costco is running, but right now it's $150 off Bridgestones I'm not interested in. The 35's on there right now are too big.
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Old 08-19-2020, 02:56 PM   #14
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Then Id probably look to step down to 285s, anything smaller will look off in proportion and too small in my opinion, see how feels before doing any gearing change. Going from 35s(315) to 285 is significant enough to notice a difference in gearing and engine performance.
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Old 08-19-2020, 03:09 PM   #15
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Then Id probably look to step down to 285s, anything smaller will look off in proportion and too small in my opinion, see how feels before doing any gearing change. Going from 35s(315) to 285 is significant enough to notice a difference in gearing and engine performance.
Anything will be an improvement over the 245/16s the original owner had on it!
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Old 08-20-2020, 02:16 PM   #16
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While doing a re-gear you may run into other things that might need replacing. Be prepared for those kind of surprises. Look into swapping from stock limited slip to an Eaton Detroit TruTrak. When we did the rear end two years ago, the costs were equal.
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Old 08-25-2020, 05:22 PM   #17
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Do you have experience with your 4r75e not lasting? im running factory 20" 2015 take offs , with the 5.4
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Old 08-28-2020, 08:37 AM   #18
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The formula is new tire size divided by factory old tire size times current gear ratio. That keeps it stock and the transmission in the same shifting rpms. But every one seems like to run at a higher rpm for more power and less mpg. Ford declined that drive train for fuel economy. At least mine 1999 e-350 5.4 with 4r100. My formula is 35/30.5x3.55=4.07
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Old 07-31-2021, 12:44 PM   #19
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I'm considering re-gearing from 3.73's to 4.10's........


I have a kingpin Dana 60 on the front and the stock full floater on the rear (2008 Passenger RB).


Will this require a different carrier F or R?
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Old 07-31-2021, 01:26 PM   #20
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I'm considering re-gearing from 3.73's to 4.10's........


I have a kingpin Dana 60 on the front and the stock full floater on the rear (2008 Passenger RB).


Will this require a different carrier F or R?
The carrier split is 4:56 I'm pretty sure.
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