Re-gearing: what size gears?

dan lee

dan lee

TJ Addiction
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Berthoud, CO, United States
So, I have a 2004 Jeep LJ Unlimited, it currently has a automatic, with 33" tires. I don't plan on going any bigger. I would like to get better highway performance then off road performance. I would like to get to the trails happily, willing to trade off, off road performance since I am not a hardcore wheeler.
 
I've had a few quotes from shops, they are recommending 4:56 gears. yes I do have the 44 in the rear and 30 in the front. Just not sure on what direction I should go
 
dan lee said:
I've had a few quotes from shops, they are recommending 4:56 gears. yes I do have the 44 in the rear and 30 in the front. Just not sure on what direction I should go
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5.13 - your automatic transmission has a . 69 overdrive ratio. Aside from the fact that 4.56 isn't enough change from 3.73 to be worth the expense of a regear, if you install 4.56 gears your rpms at interstate speeds will be far too low.
 
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As everyone above has said, go directly with 5.13. I have direct experience as I had my previous 2004 TJ Rubicon with the auto and 33s regeared to 5.13 (honestly I wished I had gone with 5.38). Since you are limited to 5.13 with your front Dana 30, go with that.
 
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dan lee said:
I've had a few quotes from shops, they are recommending 4:56 gears. yes I do have the 44 in the rear and 30 in the front. Just not sure on what direction I should go
Click to expand...
Your shops don't know WTF they're talking about, 4.56 is only appropriate for 33" tires with either a 5-speed manual transmission or a big V8 truck. Your automatic transmission has a .69 Overdrive ratio that drops the engine rpms much more than most other transmissions so you need to gear the axles to a lower ratio than most would think appropriate for 33" tires. 4.88 is the bare minimum to give you decent highway rpms with your 42RLE automatic transmission but personally I'd go with 5.13.

With 5.13 and 33's you'd only be turning over 2355 rpms at 65 mph. With 4.88 you'd only be turning over 2255 rpms at 65 mph which really isn't quite enough for the highway. Not to mention you'd likely get better mpg with the slightly higher rpms of 5.13 since the engine won't be on the verge of lugging like it would be at only 2255 rpms.

4.88 and 5.13 are both suggested with primarily street use and produce highway appropriate rpms in mind, they are definitely not "hardcore" ratios meant primarily for offroad use.
 
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dan lee said:
Thanks for all the input, looks like 5:13 it is
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Good decision Dan. And pay absolutely no attention to a clueless shop guy pretending to be an expert and try to talk you out of 5.13 claiming its pinion is not strong enough. Low ratio ring and pinion gears were redesigned years ago so they have the same gear tooth engagement that higher ratio gears do.
 
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FWIW, Dan:

2006 TJ 2.4L, 6-speed manual NSG370 tranny, 3” Teraflex lift, 33” tires.

With guidance from Jerry Bransford:

— I upgraded from 3.73 to 4.56 with "Yukon front and rear ring and pinion for Dana 30 Front / Dana 35 Rear" - https://www.quadratec.com/p/yukon-g...tall-kits-jeep-wrangler-tj-dana-30-front-dana

— I added an "EATON 912A569 Trutrac limited slip diff for 27 Spline Dana 35 Axle with 3.54 and Numerically Higher Gear Ratio" - https://www.quadratec.com/products/16100_603.htm

— went with Alloy USA diff covers – heavy duty aluminum alloy, lightweight, strong, affordable and perhaps most importantly, superior heat disbursement vs cast steel/iron - https://www.alloyusa.com/differential-covers.html

Results were immediately noticeable – I’m a gear higher at every speed. Summary in advance: after 17 years, I’m finally comfortable driving a dinky 2.4L – more power in the wind and on the highway, higher cruising speed and lower RPMs.

Obviously not an automatic like you have.

IMG_20210718_103024_545.jpg


IMG_20210718_103024_561.jpg


IMG_20210718_103024_564.jpg
 
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I am running same engine and transmission as yours.
With our 4 speed auto, 4.56 is a minimum for 31s, 4.88 minimum for 32s and 5.13 for 33s.

I have 4.56 gears with 31s, and I wish I would go 4.88. This would match my 31s better. However, even with 4.56 it drives nice. Far better than with stock 3.73 gears
 
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dan lee said:
So, I have a 2004 Jeep LJ Unlimited, it currently has a automatic, with 33" tires. I don't plan on going any bigger. I would like to get better highway performance then off road performance. I would like to get to the trails happily, willing to trade off, off road performance since I am not a hardcore wheeler.
Click to expand...

Like everyone says, go 5.13, I did the 4.56 and then went to 5.13, do it once and be happy.
 
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I would say 5.13 after just having my 2006 LJ , 42RLE, 33" tires regeared to 4.88. I went with 4.88 for a number of factors but at this point I ALMOST wish I had gone 5.13. Just remember...the faster things are going the more potential you will have for vibrations.
 
Soldmytaco said:
I would say 5.13 after just having my 2006 LJ , 42RLE, 33" tires regeared to 4.88. I went with 4.88 for a number of factors but at this point I ALMOST wish I had gone 5.13. Just remember...the faster things are going the more potential you will have for vibrations.
Click to expand...

Between 40-50 mph that overdrive kicks in and youll be wishing you had went with 5.13
 
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