5.13 Gears, My Thoughts and Real Numbers

[Escape.idiocracy]

How many miles have you guys stacked on with 5.13’s/lower gears?

How often are you guys running on the highway for longer periods of time?

Mostly curious as to how well bearings etc are holding up with the higher heat produced.

I would “want” 5.38’s but will likely settle with 5.13’s. We do make several long road trips a year with sustained speeds 70-80mph. Our JK on 4.88’s I would change the fluid after every long road trip to “help” but speed and deep gears just get Hot!

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[JTenn]

How many miles have you guys stacked on with 5.13’s/lower gears?

How often are you guys running on the highway for longer periods of time?

Mostly curious as to how well bearings etc are holding up with the higher heat produced.

I would “want” 5.38’s but will likely settle with 5.13’s. We do make several long road trips a year with sustained speeds 70-80mph. Our JK on 4.88’s I would change the fluid after every long road trip to “help” but speed and deep gears just get Hot!

I haven't had them in long enough to know if there's a heat issue. But I can say I drive 100 miles a day at 75-80 mph and think nothing of it. The truck just rolls at those speeds.

 

[Volksparts]

I've been running 37s and 5.13 gears and there's no way I get those gas numbers. Granted I'm carrying a lot of weight with all my accessories but I average 9-12 mpg and best about 13 mpg. I also live in San Diego and drive a lot of hills.

 

[XraytecH]

As many of you know, I swapped my complete axle assemblies out of my 21 Willys and installed Rubicon axles with 5.13 gears. I've been running these for a week and have very quickly acclimated to the new feel of all that low end torque. Needless to say I'm very impressed and happy with my decision to install the 5.13's. If anyone is on the fence about such a steep gear, don't be. My daily commute is 100 miles and my mpg has improved about 1-1/2 mpg so far. From 15.5 to 17. I'm still on 35's for now but these numbers should improve when I go to 37's. So here are the actual rpm numbers.
55 mph- 1900 rpm
60 mph- 2100 rpm
65 mph- 2300 rpm
70 mph- 2400 rpm
75 mph- 2600 rpm
Sorry for the crappy pictures but you get the idea.
Before the swap I was generally running close to 2900-3000 rpm in 6th & 7th gear at 75 mph. Hope this helps anyone thinking about changing gears.

How's does you transmission act when you are cruising at 75 and you need to overtake someone? Does it downshift when you punch the gas?

I've researched that 37s on 5.13s at 75 the transmission will not downshift when you try to pass someone. Curios if it's the same on 35s.

 

[JTenn]

How's does you transmission act when you are cruising at 75 and you need to overtake someone? Does it downshift when you punch the gas?

I've researched that 37s on 5.13s at 75 the transmission will not downshift when you try to pass someone. Curios if it's the same on 35s.

I've not had that experience with my particular truck. It does down shift and overtakes as expected. The gearing kind of reminds me of having the effortless power of a V8 if that makes sense. The entire package is just much happier. I wonder if those that experience shifting issues ever changed the gear ratio in the programming. I did mine via the Tazer.

 

[JTenn]

I've been running 37s and 5.13 gears and there's no way I get those gas numbers. Granted I'm carrying a lot of weight with all my accessories but I average 9-12 mpg and best about 13 mpg. I also live in San Diego and drive a lot of hills.

Wow that's crazy!! It's even worse given the gas prices there. My kids are moving out of SD next week. Heading to Mississippi. They will be 4 hours away so we're excited to have them closer to home.

 

[JTenn]

How many miles have you guys stacked on with 5.13’s/lower gears?

How often are you guys running on the highway for longer periods of time?

Mostly curious as to how well bearings etc are holding up with the higher heat produced.

I would “want” 5.38’s but will likely settle with 5.13’s. We do make several long road trips a year with sustained speeds 70-80mph. Our JK on 4.88’s I would change the fluid after every long road trip to “help” but speed and deep gears just get Hot!

When I arrived at work this morning after a 50 mile trip at 70-75 mph, I crawled under the truck and laid hands on my diff. I began praying and..........lol, just kidding. Seriously though, it was, my best guess about 130 degrees. I could easily touch and leave my hands in contact with the diff. This to me doesn't seem like excessive heat but I'm not sure what a differential normally runs. I would definitely think the oil would be rated for much higher Temps though. I will probably plan to change the oil every 15000 miles although I think that's more than it needs. I'll lean towards the side of caution though.

 

[MrClortho]

I appreciate your input on this. I currently have 3.73s with the stock 31"-32" mud tires and it isn't enough gear. I have to force the transmission to stay in 8th manually at highway speeds if there is any wind or any incline at all. That lead me to believe 4:10s or lower would be about right for stock. When playing around, I felt that about 2,700 rpm was a sweet spot in the power curve and fuel economy did not suffer or maybe was a little better.

After installing a 2.5" level, rock sliders, skid plates, bumpers and a winch, the weight of the JT has increased and the aerodynamics decreased, so it needs even more gear in my opinion. I am installing 35's next week and am researching the 4.88 vs 5.13 change. According to your information, if 75mph is about 2,600rpm with 35's then 5.13s sound like the way to go, especially if I go up to 37's in a few years.

Again, thank you for posting!

 

[hjdca]

How many miles have you guys stacked on with 5.13’s/lower gears?

How often are you guys running on the highway for longer periods of time?

Mostly curious as to how well bearings etc are holding up with the higher heat produced.

I would “want” 5.38’s but will likely settle with 5.13’s. We do make several long road trips a year with sustained speeds 70-80mph. Our JK on 4.88’s I would change the fluid after every long road trip to “help” but speed and deep gears just get Hot!

On my stick shift JTR, I have about 35K miles on my Dana Spicer 5:13s with 37's. I live in a hotter climate in the So Cal mountains. I have taken trips to the Rubicon trail (8 hours), Sedona (11 hours) and Big Bear (3 hours). I run the recommended for towing Mopar synthetic gear oil 75w140 in both diffs. with no additive. I have changed it 2 or 3 times. I run metalcloak Nodular Iron diff covers and I fill the diffs with the Jeep Gladiator recommended amount. I have had zero issues, no noise, no whining, no leaks.

 

[gt3mike]

I recently changed to 5.13 on my JTR with 35s. I've driven close to 700 miles, and the transmission is still unhappy. It's holding gears unnecessarily (for example yesterday I needed to force it to upshift from 5th to 6th at around 70mph). Also it sometimes shifts down to 1st gear when stopping, which can be abrupt.

Yes, I updated the computer for the 5.13 gear ratio. Twice.

Did anyone here that changed to 5.13 gearing and has a happy transmission do anything to reset the transmission "memory"? If so, what did you do? I can take it to Jeep, but that path usually leads to frustration.

 

[Escape.idiocracy]

On my stick shift JTR, I have about 35K miles on my Dana Spicer 5:13s with 37's. I live in a hotter climate in the So Cal mountains. I have taken trips to the Rubicon trail (8 hours), Sedona (11 hours) and Big Bear (3 hours). I run the recommended for towing Mopar synthetic gear oil 75w140 in both diffs. with no additive. I have changed it 2 or 3 times. I run metalcloak Nodular Iron diff covers and I fill the diffs with the Jeep Gladiator recommended amount. I have had zero issues, no noise, no whining, no leaks.

This is good to hear. We used to live just outside Death Valley- Ridgecrest so I hear you/understand with the heat. You changing every 15k? or 10k? What speeds are you usually running on the highway for your trips?

Thanks for all of your notes, its appreciated. (Y)

 

[hjdca]

This is good to hear. We used to live just outside Death Valley- Ridgecrest so I hear you/understand with the heat. You changing every 15k? or 10k? What speeds are you usually running on the highway for your trips?

Thanks for all of your notes, its appreciated. (Y)

I have not noticed any problem with heat. I had Rebel off-road install the Dana Spicer 5:13 gears at around 20K miles. Rebel off-road told me to use 140w oil. I changed the both diff oil, 500 miles later with Mopar synthetic 75w140. At 27K miles, I changed just the rear diff with Mopar synthetic 75w140. At 44K miles, I changed both diffs with 75w140. I am at roughly 54K miles now. I drive city and fwy, always going as fast as I can without getting a ticket. So, 73- 75 mph normally; 80-83 mph when there is no traffic. I basically drive the same speed that I did with the 4:10 gears. I have not changed my driving habits. I get the best mileage at 65 mph. I followed a friends motorhome back from Sedona, and I got an incredible 20 mpg -- calculated by hand with google miles and gallons filled at the pump. It was mostly all flat run. Normally, with all the hills around me and the aerodynamics with the speed I drive, I get about 15-16 mpg. With my 37 inch tires, the 5:13s helped my gas mileage more than hurting it. I have never towed with my stick shift JTR.

 

[MrClortho]

I now have 35's and the stock 3.73 gears and 8th gear is useless. In 7th gear, at 80mph, I am at 2600 rpm. This seems to be about the perfect RPM for that speed and got about 16mpg. The Jeep would hold 80mph in wind and only drop 1-2 mph up hills. Any less RPM and it probably would not have sustained the speed as well.

5.13s are the way to go for sure.

 

[JTenn]

I now have 35's and the stock 3.73 gears and 8th gear is useless. In 7th gear, at 80mph, I am at 2600 rpm. This seems to be about the perfect RPM for that speed and got about 16mpg. The Jeep would hold 80mph in wind and only drop 1-2 mph up hills. Any less RPM and it probably would not have sustained the speed as well.

5.13s are the way to go for sure.

As previously stated, I couldn't be happier with the gearing. With this 8 speed trans set up it is the way to go in my opinion.

 

[AustinL911]

Dana 5.13 gears with rebuild kit ordered from NR4x4 this morning now that they're back in stock (sweet Jesus, finally). Going to wait a little bit to have them installed as I'd like to see what Jeep plans to do with the stock clutch before I order a Center Force replacement, as I'd like to do it all at the same time.

JTR/6MT/35s

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