What gear for 37s - Page 2 - Dodge Cummins Diesel Forum
2013-2018 General Discussion General Chit Chat About the 2013 model year differences 6.7L 4th generation Cummins - NO ADVERTISING - Sponsored by: StarLite Diesel

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post #13 of 122 (permalink) Old 09-06-2019, 09:51 AM
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Originally Posted by Cummins_Michael View Post
Thanks for all the replies.

Couple more questions.

What rear end do I have? 11.5 or 11.8? My truck is a 3500 srw.

Also....any of you ever thought about 4.30s or 4.10 the better route?
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Originally Posted by nick00less View Post
You have an 11.8 however a 11.5 will fit. Both are in the same 14 bolt housing. They just use different bearings for their associated R&P
are you sure??
I have an '18 3500 SRW with Aisin, my build sheet says 11.5"
I have been wondering the same thing, is it 11.5 or 11.8


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post #14 of 122 (permalink) Old 09-06-2019, 10:56 AM
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Did some more digging and I need to clarify. Older 11.8ís will fit same as 11.5ís as they both use 12 bolts for the ring gear. Newer 11.8ís switched to 16 bolt

http://www.demandaam.com/pressreleas...am-3500-trucks



Hereís my 11.5 (12 bolt)




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post #15 of 122 (permalink) Old 09-06-2019, 10:59 AM
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Originally Posted by nick00less View Post
I see guys on here all the time debating over which is best. Trust me when I say this. Your rear end (your butt) will not feel a difference between those 4. The only difference will be final RPM +/- 100-300 RPM.
And this is the truth.

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post #16 of 122 (permalink) Old 09-06-2019, 11:06 AM
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There's a lot of calculators on the internet if you want to do some what if's at various speeds gears etc. Here's an example. https://spicerparts.com/calculators/...rpm-calculator
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post #17 of 122 (permalink) Old 09-06-2019, 08:40 PM Thread Starter
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So 11.5 it is?

I ordered my AAM gesrs through East Coast and they told me my rear end was 11.5...

I got 4.10s too btw.
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post #18 of 122 (permalink) Old 09-07-2019, 12:39 PM
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i have 4.56's

i guess the only complaint is running nearly 2k rpm's at 70

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post #19 of 122 (permalink) Old 09-09-2019, 11:55 AM
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Originally Posted by Cummins_Michael View Post
So 11.5 it is?

I ordered my AAM gesrs through East Coast and they told me my rear end was 11.5...

I got 4.10s too btw.
I've always understood that single rear wheel trucks, even with the Aisin, are 11.5" rear ends (mine certainly is). DRW w/ Aisin (don't know about the 68s) got 11.8s

You should be able to paste your VIN at the end of this url and get your build sheet...

https://www.dodge.com/webselfservice...etServlet?vin=

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post #20 of 122 (permalink) Old 09-09-2019, 06:04 PM
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I had 4.10's installed in my truck for 35's, if I were going to run 37's all the time I would go 4.30. I live in the hills and use my truck to haul my equipment and livestock and with the extra weight and circumference of 37's, 4.10 wouldn't be enough gear in my opinion. I'm not a mechanic, I just know what I want/need out of my truck.
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post #21 of 122 (permalink) Old 09-10-2019, 01:42 PM
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I'm running 37" Toyo open country RTs. I had 4.10s put in and have no complaints. need to update my info so it shows 37s

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post #22 of 122 (permalink) Old 09-10-2019, 04:19 PM Thread Starter
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I'm running 37" Toyo open country RTs. I had 4.10s put in and have no complaints. need to update my info so it shows 37s
Do you wish you would have gone 4.30?

What brand did you go with as well?

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post #23 of 122 (permalink) Old 09-11-2019, 08:13 AM Thread Starter
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More questions for the experts.

After break in, do I need to change front and rear oil?

What oil do yall reccomend as well?

Thanks

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post #24 of 122 (permalink) Old 09-11-2019, 08:57 AM
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Originally Posted by Cummins_Michael View Post
More questions for the experts.

After break in, do I need to change front and rear oil?

What oil do yall reccomend as well?

Thanks
Yes

75/90

Doesnít matter brand but to answer your question I went with valvoline.

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