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Discussion Starter · #1 ·
I was curious if 4.09 4.10 and 4.11 are all the same count ring and pinoin? the reason why i ask i was thinking about running a scout front axle and a amc 20 in the rear, i have never heard anyone say i want 4.09 in my amc 20? do they make 4.09 or are they all the same gear set?
thanks in advance
andy

 

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without going into a long explanation, they are close enough to be considered the 'same'. the number comes from the number of teeth on the ring gear divided by the number of teeth on the pinion. different differentials have different ring gear diameters and the rest cascades from that. use the 4.10 for the 20 and the 4.09 for the 44.

79/CJ-7/AMC360/TH400/Q-TRAC/d30/d44/33's/RS9000s/Herculiner/Pro-jection 2D
 
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Discussion Starter · #3 ·
here is some quick figures: 4.11:1-37/9, 4.10:1-41/10, 4.09:1-45/11. these are all functionally interchangable, different manufacturers end up with slightly different ratios because of design considerations of ring gear diameter and distance from ring gear to pinion center line. how many vehicles have different brands of differentials front and rear? Hmmm... jeep, ford, chevy, dodge, international..

 

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So looking at the ratios (thanks for posting them BTW), it seems the 4.09's would be stronger than the 4.11's? In case anyone is wondering, the Scout II axles (D44's) used the 45/11 = 4.09 setup. I just round it off to 4.10 'cause it's easier to say and I'm lazy.

JEEPN
'81 CJ-8 Scrambled!
GM151/SM465/NP205 twinstick/7"Lift/33"TSL's/IHC D44's 4.10's Lock'd
 

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Isn't it true that gear makers try to avoid even numbered gears such as 4.10. If you had a true 4.10 ratio the pinion teath and ring
teeth would touch the same gear every revolution. Isn't that why the gears are 2.73, 3.54, 3.73, 4.56. Dont' those gears allow
for different teeth to contact on each revolution. Am I right?

Alec

 

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/wwwthreads_images/icons/smile.gif Only one of the gears has to be an uneven number, and even at that, the gear will still "walk the circuit" as long as it's number of teeth is not evenly divisible into the larger gear. We do the same thing for chain sprockets when they are used on double-pitch chains drives./wwwthreads_images/icons/crazy.gif

CJDave
I never believe any statistics unless my moonguys /wwwthreads_images/icons/crazy.gif/wwwthreads_images/icons/wink.gif made 'em up themselves.
 

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The Dana/Spicer gearset (generally considered to be the best and easiest to install) is a 4.09. So long as the front and rear differentials are within 1% of each other, they will work just fine. 4.11 and 4.09 are within 1%, so as long as you say "4.10" over the phone, you'll get a set that works.

 
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Discussion Starter · #8 ·
In contrary response to what JEEPN said, I always figured 4.11s would be stronger than 4.09s if both had the same size ring gear. Correct me if I'm wrong, but if there are fewer teeth on a given surface (in this case 37 for the 4.11 ratio vs. 45 for the 4.09 ratio), that means they would have to bigger and that would mean stronger. It's just a thought and... well... sometimes I'm not too good at thinking!
But I'd be interested to hear the verdict on this if anybody knows for sure.
That way, if somebody wants to beef up their Dana 30 and keep it in a ratio with a close selection of gears (such as 4.10), they can actually get some that are stronger than others. Again, just a thought.

-Dorian
88 YJ w/ factory paint
 
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Discussion Starter · #9 ·
I am not sure either but keep in mind! i do not believe you have a choice of gears 4.09,4.10,4.11 on any axle it is one or the other or the other? i think that how it goes i just started researching it myself but if anyone has something better to say please jump in!
Andy

 

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My rationale is that there would be more contact surface with more teeth per gear. Take for example the axles. A 30 spline D44 is stronger than a 10 spline because of the contact area, even though the 10 spline has larger "teeth".

JEEPN
'81 CJ-8 Scrambled!
GM151/SM465/NP205 twinstick/7"Lift/33"TSL's/IHC D44's 4.10's Lock'd
 
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