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Gearing for 40's on UD60's........ 4.88 or 5.38?

MrJonnycat

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So I'm switching over to UD60's on my 392, and I'm having a hard time deciding whether to go 5.38's or 4.88's on 40's. It's my daily driver, and I do use the freeway from time to time as well, but I'm not sure if the 5.38's will be too much for it. Knowing the transfer case is 2.72:1, and NOT 4:1 like all my other Rubicon's I want a good crawl ratio. I would love to go 5.13's, but that's not offered. Anyone have any real world experience with this?

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GATORB8

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Looks like 4.88s will get you the closest to stock, but 5.38s will get your crawl to 73:1 without too much highway impact. Here's the calcs from grimmjeeper.

Stock:

TC HITC LO1TC LO2TC HITC LO1TC LO2
GearUnderdrive HiUnderdrive Lo
Final Drive Ratio
120.5055.76----
213.1235.69----
38.7723.87----
47.0519.18----
55.3714.61----
64.1011.15----
73.369.14----
82.627.14----
9------
10------
R14.1938.59----
The following chart lists the crawl speed you will be going while the engine is at a given RPM. Crawl speed is calculated based on the lowest low range (transfer case and underdrive in low range) available in your rig.

FPMMPHFPMMPHFPMMPH
Gear RPM RPM RPM
Crawl speed at given RPM in feet per minute and miles per hour
11151.314615.2492210.48
21802.057208.18144016.37
32693.06107712.24215424.48
43353.81134015.23268030.45
54405.00175919.99351839.98
65766.55230526.19460952.38
77037.98281031.94562163.87
890010.23360140.92720281.84
9------
10------
R1671.896667.57133215.14


The following chart lists the road speed you will be going while the engine is at a given RPM. Road speed is calculated based on the transfer case and underdrive being in high range.

Gear RPM RPM RPM
Road speed at given RPM in miles per hour
141428
262245
383367
4104183
51454109
61871142
72287174
828111223
9---
10---
R52141


The following chart lists the RPMs your engine will be turning while driving at a given speed.

Gear
Road RPMs at given speed in miles per hour
12106737014740
2134847179434
390131546309
472425355071
555219313862
642114742948
734512092417
82709431887
9---
10---
R1457510010200

4.88s:

TC HITC LOTC LO2TC HITC LOTC LO2
GearUnderdrive HiUnderdrive Lo
Final Drive Ratio
124.4066.37----
215.6242.48----
310.4428.41----
48.3922.83----
56.3917.39----
64.8813.27----
74.0010.88----
83.128.50----
9------
10------
R16.8845.93----
The following chart lists the crawl speed you will be going while the engine is at a given RPM. Crawl speed is calculated based on the lowest low range (transfer case and underdrive in low range) available in your rig.

FPMMPHFPMMPHFPMMPH
Gear RPM RPM RPM
Crawl speed at given RPM in feet per minute and miles per hour
11171.334685.3193510.63
21832.087318.30146116.61
32733.10109312.42218524.83
43403.86135915.45271930.90
54465.07178520.28357040.56
65856.64233826.57467653.14
77138.10285132.40570364.80
891310.38365341.52730783.03
9------
10------
R1691.926767.68135215.36


The following chart lists the road speed you will be going while the engine is at a given RPM. Road speed is calculated based on the transfer case and underdrive being in high range.

Gear RPM RPM RPM
Road speed at given RPM in miles per hour
141429
262345
383468
4114284
51455110
61872145
72288176
828113226
9---
10---
R52142


The following chart lists the RPMs your engine will be turning while driving at a given speed.

Gear
Road RPMs at given speed in miles per hour
12076726414529
2132846499298
388831096218
471424994998
554419033807
641514532906
734011912383
82669301860
9---
10---
R1436502710054

5.38s:


TC HITC LOTC LO2TC HITC LOTC LO2
GearUnderdrive HiUnderdrive Lo
Final Drive Ratio
126.9073.17----
217.2246.83----
311.5131.32----
49.2525.17----
57.0519.17----
65.3814.63----
74.4112.00----
83.449.37----
9------
10------
R18.6150.63----
The following chart lists the crawl speed you will be going while the engine is at a given RPM. Crawl speed is calculated based on the lowest low range (transfer case and underdrive in low range) available in your rig.

FPMMPHFPMMPHFPMMPH
Gear RPM RPM RPM
Crawl speed at given RPM in feet per minute and miles per hour
11061.214244.828489.64
21661.886637.53132615.06
32482.8299111.26198222.52
43083.50123314.01246628.02
54054.60161918.40323836.79
65306.03212124.10424248.20
76477.35258629.39517358.78
88289.41331437.66662875.31
9------
10------
R1531.746136.97122613.93


The following chart lists the road speed you will be going while the engine is at a given RPM. Road speed is calculated based on the transfer case and underdrive being in high range.

Gear RPM RPM RPM
Road speed at given RPM in miles per hour
131326
252041
383161
4103876
51350100
61666131
72080160
826102205
9---
10---
R51938


The following chart lists the RPMs your engine will be turning while driving at a given speed.

Gear
Road RPMs at given speed in miles per hour
12288800916017
21464512610251
397934286855
478727555510
560020984197
645816023203
737513132627
829310252050
9---
10---
R1583554211084

 

chevymitchell

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These charts do a great job at providing an RPM comparison.

The math I mention should include a mass compensation variable.

4.88's would be closest to stock at stock weight.

Drivability would be more my concern rather than finding a suitable RPM.

Whatever the net weight gain is from stock to modified, add 10% for a loaded, wheeling configuration. (Easily 500 lbs for people and gear.)

EDIT: Just FYI. I ordered an XD60/80 axle set-up from Dynatrac with 5.38's and I will be running a 40", as well.
 
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ozon8r

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Jon, What if you want to go to 42s? If you go 5.38s, you will be ready once you tire (PUN INTENDED) of the 40 shoes. And at the rate you re-shoe your 392, I bet you will be lusting after something bigger than 40s real quick. And tons will be beggin you to go bigger, LOL.
 

jellis4148

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I'm going to do the UD60's, and 5.38. Granted I have the V6, but my thoughts are when running 40's, and all the extra weight of the axles, beadlocks, and tires the 5.38 will make up for that. I have no math to back up my answer, but it seems logical.
 

MSparks909

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IMO, 5.38s seems deep to me especially with the Hemi. She will be singing on the highway. Lite Brite is running 5.13s in their Dynatrac XD60/80. What 40s are you going to run? If theyā€™re light you could always do 4.88s and swap in a standard Rubicon 4:1 Transfercase. Gets you a solid crawl ratio and wonā€™t kill your highway mileage
 

Outrun

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4.88 because this transmission just ain't the same as a JK.
 

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MSparks909

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Bump. Anyone have any 5.38/40ā€ drivability reports?
 
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MrJonnycat

MrJonnycat

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I ended up going with Fusion 4 x 4ā€™s K Fusion Elite Series 60ā€™s set up. Eaten E lockers front and rear and 5.13 gears. They are installing 35 spline RCV AXLES up front and upgraded 40 spline axles in the rear. I figure that should be able to handle anything I throw at it even in 2 WD. šŸ˜œ
Jeep Wrangler JL Gearing for 40's on UD60's........ 4.88 or 5.38? 5E460B2F-F1CE-448B-88B9-6347A49F02E1
 

Qwest4air

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Does anyone else have fusion axles installed in a jl? Iā€™m in the process of installing some now and have some clearance issues in the up travel on the driver side, the tire rod wants to collide with the Pitman arm off the steering gearbox.

And itā€™s current set up Iā€™m only gonna have about 2 inches of up travel on a 3 1/2 inch lift.
 

Qwest4air

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It may not be as bad from an articulation standpoint, but if I ever went fast and hit a dip when the entire axle cycles up together I think itā€™s gonna be a problem. Has anybody found any workarounds other than going with a flat Pitman arm and notching the crossmember?
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