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Old 06-08-2014, 02:14 AM   #1
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gear ratio change, what makes sense?

Hello

as some here know i drive a E350 4x4 SMB with an 7.3 Weight is about 9000lbs,
Dana 60 FF in the rear and Dana Super 60 in front (out of an 2006 F250)
never will use a trailer but will go to a world trip starting in Africa (no highways)
my normal speed on the highway here in germany is 65 mls the highest 75 mls. Faster makes no sense for me....

Now to my problem

I changed from 285/75-17 to 37x12,5 and so also i have to change the gear ratio.
It is 3.73:1 now and still with the 285 it was on the edge.... fuel econmy -what is also an importand point for me- was great but in the montains i missed the bunch.
With the 37 now it is no fun any more.
My question to the specialist here.
I am thinking to go to 4.3 or 4.56 ring and pinions
Is it possible to go to these or do i need than also an other diff case?
As i have an ARB locker in the rear does that mean i need a new one?

Another question i have:
Is there a way to change the 1:1 ratio in the NV 271 transfer case to about 1.2:1 ??? That would be the easiest and cheapest way i assume.

Thanks for giving me some advices!
Didi

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Old 06-08-2014, 08:35 PM   #2
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Re: gear ratio change, what makes sense?

Go 4.56. My 7.3 also has 37's and I'm running that ratio. Same for quite a few vans we've built for customers.
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Old 06-08-2014, 10:43 PM   #3
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Re: gear ratio change, what makes sense?

What Chris said.

The 4.30 gears are cut thinner so they are weaker. I popped a pinion tooth off mine, so then I switched to 4.56. I should had gone that route the 1st time.

Check the casting number on the rear axle housing. There's a chance its a D70 housing. If it is, you can change the carrier and install 10.5" gears.

I think you might have to change carriers anyways because there is a size break at 4.10. I don't know what that means for the locker however.
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Old 06-09-2014, 11:27 AM   #4
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Re: gear ratio change, what makes sense?

Quote:
Originally Posted by carringb
I think you might have to change carriers anyways because there is a size break at 4.10. I don't know what that means for the locker however.
You can buy "thick" gears (or use a ring gear spacer) instead of switching from a series 3 carrier (which is what 3.73 and 4.10 ratios use) to a series 4 carrier (which is what 4.56 and deeper uses.)
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Old 06-10-2014, 01:04 AM   #5
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Re: gear ratio change, what makes sense?

Great informations! Thanks
If 4.3 is a unreliable option i definitly will go 4.53
Never heard about the possibility of "thick" rings or spacers! That will save me a lot of money in the rear
Do you guys have a recommendation for a locker in the front? I have an ARB in rear but think about to buy an automatic locker for the front as it is much cheaper.
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