cozdude
Guy with a Red 2-Door
moby (white 4 door) is on 40's and rubicat (orange 4 door) is on 37's
Getting 37's need hep choosing gears
- Thread starter 2me's JK
- Start date
moby (white 4 door) is on 40's and rubicat (orange 4 door) is on 37's
2me's JK
New member
At 75-80 MPH, I run about 3000-3200 RPM with my 37's and 5.13's. That's about 500 more RPM than if I were running 4.88's.
What Adam said. A Dana 30 has a smaller ring and pinion and at 5.13's, the pinion gets to be really small and will leave you with about one and a half teeth making actual contact with the ring gear. A Dana 44 has a larger ring and pinion and you won't see this problem until you get up to a 5.38.
On a 2007-11 JK with a 3.8L motor, the ratio you want with 37's is 5.13. On a 2012-up with a 3.6L motor, 4.88 will get you back up to stock performance but, I personally would still recommend 5.13. Where I would recommend a 4.88 is if you're trying to run 37's on a Dana 30. At that point, a 5.13 will leave you with a pinion that is very small and will be a weak point. In this situation, strength of your gears should trump your desire for more power.
cozdude said:
What cozdude said. :yup:
mudmobeeler
Caught the Bug
Any issues really running those RPMs? That just seems really high. I know you have done it a lot longer than me cause mine is still stock, that's why I ask. My plan is someday to go to 37s and drive it wherever I want like you all do with Rubicat and Moby.
OverlanderJK
Resident Smartass
Only issues you'll see is bad mpg on the highway at high speeds.
Nope, no problems. I ran Moby with 5.13's and 35's on a manual for a long time too and I've always liked the additional power. I should also note that I'm having a DTD and Moby's rear ProRock 60 going into Rubicat now and when all is said and done, she'll be running 5.38's. If there is a downside, it'll be that you won't get as good of MPG when driving 75+ on the highway. If you can keep the speedo at about 55-65, the difference won't be much at all.
SDG
Caught the Bug
I didnt know your speedometer went as low as 55 Eddie. Thought it went from 30 directly to 80 haha.
olram30
Not That Kind of Engineer
mudmobeeler
Caught the Bug
Not worried about fuel mileage. Like I tell people when they ask it gets in the 100s. They say "100s?" To which I say "oh you said miles per gallon, thought you said smiles per gallon. I don't check the fuel mileage on it. It's not a Prius"
Main concern was overheating etc.
Main concern was overheating etc.
2me's JK
New member
Wayalife : "Where I would recommend a 4.88 is if you're trying to run 37's on a Dana 30. At that point, a 5.13 will leave you with a pinion that is very small and will be a weak point. In this situation, strength of your gears should trump your desire for more power."
Ok,
I'm really sold on the idea of the 5.13 for power but:
I'm concerned about the 5.13 since I still have the stock Dana 30 Solid Front Axle, and will have the stock axels for quite a few years.
I'm adding a full Artec Truss kit front & rear.
I need this to be bullet proof with no worries the first time around.
So it may have to be 4.88's?
Food for thought, here is a list of equipment that is being installed, the 4.88 gears that is listed is there as a place holder while I decide on the actual gears.
Yukon D30 Short Reverse 4:88 Ring & Pinion, Front JK 24 Spline
Yukon USA Standars D30 Front Install Kit JK
TEN Factory Front Axle Tube Seals For 84-14 Jeep® Vehicles with 30 Spline Dana 30/44 Front Axle
Yukon 4340 Chrome-Moly Axle Kit for Dana 30 Front, Non-Rubicon JK,
ARB Air Locker Dana 30 27 Spline 3.73-Up
USA Standard replacement Ring & Pinion gear set for Dana 44 JK rear in a 4.88 ratio
USA Standard Master Overhaul Kit for the Dana 44 JK non-Rubicon
Rear Differential
ARB Air Locker For D44
Yukon 4340 Chrome-Moly replacement rear axle for
Dana 44, 30 spline
SET10 Axle Bearing & Seal Kit for D44 & M20
ARB High Output OnBoard Air Compressor
Synergy Suspension Air Compressor Bracket
Amsoil Severe Gear Synthetic EP- 75W -140
Your thoughts (again)?
And thanks again for your time and advice.
JT
Ok,
I'm really sold on the idea of the 5.13 for power but:
I'm concerned about the 5.13 since I still have the stock Dana 30 Solid Front Axle, and will have the stock axels for quite a few years.
I'm adding a full Artec Truss kit front & rear.
I need this to be bullet proof with no worries the first time around.
So it may have to be 4.88's?
Food for thought, here is a list of equipment that is being installed, the 4.88 gears that is listed is there as a place holder while I decide on the actual gears.
Yukon D30 Short Reverse 4:88 Ring & Pinion, Front JK 24 Spline
Yukon USA Standars D30 Front Install Kit JK
TEN Factory Front Axle Tube Seals For 84-14 Jeep® Vehicles with 30 Spline Dana 30/44 Front Axle
Yukon 4340 Chrome-Moly Axle Kit for Dana 30 Front, Non-Rubicon JK,
ARB Air Locker Dana 30 27 Spline 3.73-Up
USA Standard replacement Ring & Pinion gear set for Dana 44 JK rear in a 4.88 ratio
USA Standard Master Overhaul Kit for the Dana 44 JK non-Rubicon
Rear Differential
ARB Air Locker For D44
Yukon 4340 Chrome-Moly replacement rear axle for
Dana 44, 30 spline
SET10 Axle Bearing & Seal Kit for D44 & M20
ARB High Output OnBoard Air Compressor
Synergy Suspension Air Compressor Bracket
Amsoil Severe Gear Synthetic EP- 75W -140
Your thoughts (again)?
And thanks again for your time and advice.
JT
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2me's JK
New member
So even with the beefing up of axels (see my list above) and I'll probably be more durable on 4.88's.
Tough decision.
Thanks again,
Jimbo
JT
For what it's worth, on my JKU Sport AUTOMATIC, I installed 4.88's when I installed 37's. This was about 800miles ago.
When I saw the tiny pinion size of my4.88's, I couldn't imagine anything lower going in to the D30. :shock:
I'm very happy with the setup. Speed limit on the freeway in my area is 70, but I find that if I exceed 65, my mpg drops about 2mpg. Vader's happy at about 60mph. This past weekend, I averaged 17.2 mpg over an 85mile trip on the freeway with a few light grades.
For what I do with the family, 4Lo works great with this gearing.
Are you having a shop install everything or DIY?
When I saw the tiny pinion size of my4.88's, I couldn't imagine anything lower going in to the D30. :shock:
I'm very happy with the setup. Speed limit on the freeway in my area is 70, but I find that if I exceed 65, my mpg drops about 2mpg. Vader's happy at about 60mph. This past weekend, I averaged 17.2 mpg over an 85mile trip on the freeway with a few light grades.
For what I do with the family, 4Lo works great with this gearing.
Are you having a shop install everything or DIY?
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2me's JK
New member
- I'm still wrecked from the car accident in December, can't do anything myself, which sucks because here in Central Florida labor is at a minimum of $85 at the shop and $100 an hour at 4 wheel parts !
It's a great shop and they work with you where they can on the parts.
I'm going too with 4.88's
Even though my motto is: "buy once, cry once" when Wayalife said he recommends 5.13's with 37's EXCEPT on a Dana 30.
That made up my mind to go with the 4.88's...
The three things that kept me from 5.13's:
Size of ring & pinion, only 1 1/2 tooth engaged
Having a stock Dana 30, even though I'm going to install the full Artec truss kit front & rear
Highway RPM's
I think I will be happy with the 4.88's especially on the highways.
After a few years, I'll see about some Dynatrac axels...
Pavement Ends
RedSyndrome
Member
I know we all have budgets, but at this point, why not stretch it out and get the pro-rock 44? $2700 well invested, and you could probably get it out-fitted as a package with most of these items and drop 1 or 2 and save a few bucks and be truly closer to bullet proof.
2me's JK
New member
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