5:38 gears questions - Page 2 - JKowners.com : Jeep Wrangler JK Forum
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post #26 of 45 Old 11-15-2018, 01:53 PM
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post #27 of 45 Old 11-15-2018, 02:45 PM
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I appreciate the video (with no scientific evidence or explanation) but in it you state the gears have the same amount of teeth but your website itself displays a different pinion tooth count for 4.88's and 5.38's which is expected. Then she also says this 5.38 gear ratio is made for that 37" tire and we should trust the manufacturer. I think that is a crap statement because the reality is the Jeeps have D44's because they only have 32" tires from the manufacturer and the real need to change gears was meant to adjust load/rpm's based on the manufacturer tire. Just because we love to shove 37" tires onto it doesn't mean that a D44 intended to ever have a tire that large which is why they make D60's and larger. The pinion diameter isn't the issue and I have never heard of someone snapping that, it's the strength of the teeth based upon amount of teeth and contact angles which is why D60's have a larger ring gear and is stronger.

Then she says the major rumor is this pinion is smaller than this one and it simply isn't the case (without a breath she says) Yes it is slightly smaller LOL (sorry but that cracked me up) Smaller =less metal and if it is the same substance it means it is weaker. But the bigger reason is due to torque, tooth contact, angle as outlined below

From Pirate 4x4
"Deep gears are weaker than tall gears. There are probably exceptions when comparing two gears of similar ratio, like a 4.88 and 5.13.

First, ignore the number of teeth. The gear ratio is the difference in diameters of the ring and pinion (I forget if its called base or root or whatever). So, small pinion, deep gears right?

Now, lets look at what the pinion is doing. It takes a certain amount of torque from the t-case and pushes against the ring gear, resulting in a force at the contact point. Now think leverage, a bigger pinion will have more leverage AND THE FORCE AT THE CONTACT POINT WILL BE LOWER!

So, a smaller pinion has less leverage (smaller diameter) and causes higher forces on both pinion and ring gear teeth.

Second, we are talking about a hypoid gear that engages more than one tooth at the same time. More teeth and a larger diameter increase the "contact area" between gears, reducing wear.

Third, there is tooth size. Lets look at Spicer sets for a Dana 44. I would view these as well-engineered gears.

ratio R P

4.11 45 11
4.88 44 9
5.38 43 8


The ratio tells us the comparative size of the base circles, so the ring on the 5.38 is biggger than the 4.88 (duh). But it takes fewer teeth (43) to go around this bigger circle, so the teeth must be bigger than on the 4.88.

The pinion has torque, got it. Imagine we put a wrench on the pinion nut and are trying to keep it from turning, small pinion is like a standard wrench, big pinion is like putting a cheater on the wrench, you push less (lower force) for same torque.

The physics is that torque is force times distance. The torque is the same in both cases. With a small pinion, we have less distance, so the force has to be bigger."

My question is - More force on the same diameter part means it will be under more stress to do the same job, hence more likely to break a 5.38 before the 4.88. Isn't than the definition of Weaker????
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post #28 of 45 Old 11-15-2018, 03:35 PM
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I wish someone would build a bench test jig, the same way RCV tests their shafts, or ARB has tested the strength of their cases so we could finally see exactly how much torque it takes to break each ring gear set. At the end of the day, it still comes down to how you drive it. If you have a heavy foot and a stubborn will, youíre going to be more prone to break things.
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post #29 of 45 Old 11-15-2018, 07:23 PM
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Originally Posted by jsukey View Post
I wish someone would build a bench test jig, the same way RCV tests their shafts, or ARB has tested the strength of their cases so we could finally see exactly how much torque it takes to break each ring gear set. At the end of the day, it still comes down to how you drive it. If you have a heavy foot and a stubborn will, youíre going to be more prone to break things.
all valid points of consideration but you omit critical,more granular factors such as the treatment of the ring gear ( cry'oed? Heat treated ) not to mention the previously referenced gear mesh / backlash the installer found they were w/in spec for , other elements such as lubrication , shaft harmonics , xfer case , et.al..I can go on ....

There's more at play but I think you are right; anyone can break something. 😉



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post #30 of 45 Old 11-16-2018, 05:00 PM
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She stated that the rumor is generally that the pinion head on a 5.38 is "MUCH" smaller & and that isnt the case, yes, it is "SLIGHTLY" smaller...but not enough to call into question strength.

The D44 JK Pinions on all 3 ratios made by Nitro Gear 4.88-5.38 have 8 Teeth - The tooth count contact is 4 at any given time, we looked...of course give or take a little variance on that 4th tooth in contact in relation to "how much contact" you're talking. While the Dana 44 was not "designed" with 37s in mind, that is what the aftermarket world has adapted to. When it comes to the literally 10s of thousands of JK gears we've sold, we've never seen somebody shear teeth SOLELY due to 5.38 ratio while running a 37" tire. That only seems to happen with JK owners who have given it a new & much high HP motor.
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post #31 of 45 Old 11-17-2018, 06:20 PM
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Originally Posted by justdifferentials View Post
She stated that the rumor is generally that the pinion head on a 5.38 is "MUCH" smaller & and that isnt the case, yes, it is "SLIGHTLY" smaller...but not enough to call into question strength.

The D44 JK Pinions on all 3 ratios made by Nitro Gear 4.88-5.38 have 8 Teeth - The tooth count contact is 4 at any given time, we looked....
Should have looked harder because like I posted earlier... they don't

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And there are a ton of people that have sheared 5.38's on 37's with a D44 and you don't even need to do a search on the forum to find the hundreds of times it has happened... just look at post 16 of this thread for one example:

Quote from post 16 "I ran 5.38 on 37's for about 6 years without issue. I first broke a rear ring and pinion towing a small ski boat to the lake not far from home. Then I'd randomly brake a rear ring and pinion every 6 months afterward. The third time, the ring bolts backed out and completely sheared off, grenading the rear axle from inside."

Granted , anytime someone decides to go to 37's or larger on a Dana44 they are asking for something to break doesn't matter if your on 4.11's or 5.38's because those tires are too large for the axle and I know "people do it all the time with no issues" but it comes down to how you wheel. Because the larger tire creates more torque in the same stress situation as a 35, a 37 will be more likely to cause a breakage (just like a breaker bar on a rusted bolt). Same as you increase the torque by re-gearing, the engine doesn't work as hard (like your arm on a breaker bar). But the force on the gear teeth or other parts increases (like the bolt that the breaker bar is trying to turn). That little crappy 3.8 is more than capable of twisting drive shafts and breaking axles as there are thousands of videos on YouTube showing JK's doing just that.

I agree with the statement that a 5.38 gear usually recommended for tire sizes 40 and up... but let's be honest that statement "usually" means for a D60 or larger because no one truly "recommends" a 37+ tire for a D44 and the only reason people do it is because they don't want to spend a crap ton on D60's and want to try to get away with it. If you baby it you can do it, those that don't end up getting D60's. If the Jeep came with D60's you certainly wouldn't have anyone switching to a D44 for 37's to gain a little more clearance or lighten the load LOL

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post #32 of 45 Old 11-20-2018, 04:09 AM
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5.13 , 5.38 and 4.88

I'm in a similar boat. I have a 08 JKU auto on 35's with 3.73. it's my daily and I drive the shit out of it, 50-60 ish miles a day just in my work commute. several of the shops in and around OKC have priced out re-gearing and locking up my D30 front and 44 rear for around $3500-$4000. every time they ask wut gear ratio I ask about 5.13 because of the slushbox auto, every shop has suggested 4.88's. but on most forums, most opinions lean towards 5.13s or 5.38s regardless of tire size (35 or 37s). So I guess I'm still on the fence about wut gear ratio to pick since I drive it a lot the 4.88s and sticking with 35s may be a safe bet (lots of highway) . shit, I guess if I go to 4.88 and don't like it 1. it will still be better than the 3.73 and 2. its only money right they print more every day.

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post #33 of 45 Old 11-20-2018, 05:58 AM
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Quote:
Originally Posted by Donut707 View Post
I'm in a similar boat. I have a 08 JKU auto on 35's with 3.73. it's my daily and I drive the shit out of it, 50-60 ish miles a day just in my work commute. several of the shops in and around OKC have priced out re-gearing and locking up my D30 front and 44 rear for around $3500-$4000. every time they ask wut gear ratio I ask about 5.13 because of the slushbox auto, every shop has suggested 4.88's. but on most forums, most opinions lean towards 5.13s or 5.38s regardless of tire size (35 or 37s). So I guess I'm still on the fence about wut gear ratio to pick since I drive it a lot the 4.88s and sticking with 35s may be a safe bet (lots of highway) . shit, I guess if I go to 4.88 and don't like it 1. it will still be better than the 3.73 and 2. its only money right they print more every day.
I believe 5.13ís would be perfect for you with your auto and 35ís. I personally wouldnít even bother with trying to beef up your Dana 30 if you intend to wheel it. Save that money and throw it at a Dana 44 or even a PR44. Just try to imagine where you want your Jeep to end up, and aim at that goal. You will save yourself a heep of money in the long run!

I would definitely look at a reputable shop to do that. $3500-$4000 for just gears and a front locker sounds high. You didnít mention what kind of locker, whether or not you were doing a rear locker and/or chromo shafts, and if you already had a tuner to recalibrate your speedo though. You wonít need a new front carrier since youíre already running 3.73. Off the top of my head, you should well under $3000 total for front and rear ring and pinion, master overhaul kits, a quality locker like ARB or Ected, and labor. With Black Friday this week, look for shops that are running specials.
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post #34 of 45 Old 11-20-2018, 10:07 AM
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I think it is nuts to spend $4k on gear install (specially putting more money on a D30)...but that is another discussion.

5.13s with 37s and auto is the sweet spot. I had it in my rig and it did very well as far as offroad and road manners.


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post #35 of 45 Old 11-20-2018, 12:20 PM
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For what it’s worth, I’ve run 37s and 5.38 Yukon gears in my ‘09 JKUR automatic for the last 45,000 miles with no issues whatsoever. I originally installed 4.88s and the combination was the suck with 37s. I’m in mountainous SW Colorado at 7500 ft. I’m 3 hours from Moab and am over there on the trails probably ten trips a year. With 37s and 5.38s higheay cruising rpms are virtually identical to stock. For a 3.8L and 37s it’s a near perfect match. If you plan to stay with 35s go 5.13s. If you go 37s later they’ll still be acceptable.
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post #36 of 45 Old 11-27-2018, 03:32 AM
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Quote:
Originally Posted by jsukey View Post
I believe 5.13ís would be perfect for you with your auto and 35ís. I personally wouldnít even bother with trying to beef up your Dana 30 if you intend to wheel it. Save that money and throw it at a Dana 44 or even a PR44. Just try to imagine where you want your Jeep to end up, and aim at that goal. You will save yourself a heep of money in the long run!


I would definitely look at a reputable shop to do that. $3500-$4000 for just gears and a front locker sounds high. You didnít mention what kind of locker, whether or not you were doing a rear locker and/or chromo shafts, and if you already had a tuner to recalibrate your speedo though. You wonít need a new front carrier since youíre already running 3.73. Off the top of my head, you should well under $3000 total for front and rear ring and pinion, master overhaul kits, a quality locker like ARB or Ected, and labor. With Black Friday this week, look for shops that are running specials.
Quote:
Originally Posted by geberhard View Post
I think it is nuts to spend $4k on gear install (specially putting more money on a D30)...but that is another discussion.

5.13s with 37s and auto is the sweet spot. I had it in my rig and it did very well as far as offroad and road manners.
Quote:
Originally Posted by SoK66 View Post
For what itís worth, Iíve run 37s and 5.38 Yukon gears in my Ď09 JKUR automatic for the last 45,000 miles with no issues whatsoever. I originally installed 4.88s and the combination was the suck with 37s. Iím in mountainous SW Colorado at 7500 ft. Iím 3 hours from Moab and am over there on the trails probably ten trips a year. With 37s and 5.38s higheay cruising rpms are virtually identical to stock. For a 3.8L and 37s itís a near perfect match. If you plan to stay with 35s go 5.13s. If you go 37s later theyíll still be acceptable.

Thanks for all the input. I agree with everyone's points that's mostly why I haven't pulled the trigger on anything yet. I did go to multiple shops in the OKC metro, the quote on the higher end included Eaton e-locker, full axle rebuilds, and sleeving and adding gussets the D30. I did get another quote for $1500 for just gears. I did just change out the factory fenders to steel ones so now I have all kinds of room for 37s, so I'm leaning towards the 5.13s/5.38 again and not the 4.88s. but like everyone has said throwing money at the D30 is ungood. shit its only money right they print more every day
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post #37 of 45 Old 11-27-2018, 04:25 AM
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Originally Posted by Riptide9 View Post
I appreciate the video (with no scientific evidence or explanation) but in it you state the gears have the same amount of teeth but your website itself displays a different pinion tooth count for 4.88's and 5.38's which is expected. Then she also says this 5.38 gear ratio is made for that 37" tire and we should trust the manufacturer. I think that is a crap statement because the reality is the Jeeps have D44's because they only have 32" tires from the manufacturer and the real need to change gears was meant to adjust load/rpm's based on the manufacturer tire. Just because we love to shove 37" tires onto it doesn't mean that a D44 intended to ever have a tire that large which is why they make D60's and larger. The pinion diameter isn't the issue and I have never heard of someone snapping that, it's the strength of the teeth based upon amount of teeth and contact angles which is why D60's have a larger ring gear and is stronger.

Then she says the major rumor is this pinion is smaller than this one and it simply isn't the case (without a breath she says) Yes it is slightly smaller LOL (sorry but that cracked me up) Smaller =less metal and if it is the same substance it means it is weaker. But the bigger reason is due to torque, tooth contact, angle as outlined below

From Pirate 4x4
"Deep gears are weaker than tall gears. There are probably exceptions when comparing two gears of similar ratio, like a 4.88 and 5.13.

First, ignore the number of teeth. The gear ratio is the difference in diameters of the ring and pinion (I forget if its called base or root or whatever). So, small pinion, deep gears right?

Now, lets look at what the pinion is doing. It takes a certain amount of torque from the t-case and pushes against the ring gear, resulting in a force at the contact point. Now think leverage, a bigger pinion will have more leverage AND THE FORCE AT THE CONTACT POINT WILL BE LOWER!

So, a smaller pinion has less leverage (smaller diameter) and causes higher forces on both pinion and ring gear teeth.

Second, we are talking about a hypoid gear that engages more than one tooth at the same time. More teeth and a larger diameter increase the "contact area" between gears, reducing wear.

Third, there is tooth size. Lets look at Spicer sets for a Dana 44. I would view these as well-engineered gears.

ratio R P

4.11 45 11
4.88 44 9
5.38 43 8


The ratio tells us the comparative size of the base circles, so the ring on the 5.38 is biggger than the 4.88 (duh). But it takes fewer teeth (43) to go around this bigger circle, so the teeth must be bigger than on the 4.88.

The pinion has torque, got it. Imagine we put a wrench on the pinion nut and are trying to keep it from turning, small pinion is like a standard wrench, big pinion is like putting a cheater on the wrench, you push less (lower force) for same torque.

The physics is that torque is force times distance. The torque is the same in both cases. With a small pinion, we have less distance, so the force has to be bigger."

My question is - More force on the same diameter part means it will be under more stress to do the same job, hence more likely to break a 5.38 before the 4.88. Isn't than the definition of Weaker????

This is a great post. Much along the lines of I what I was showing on the recent high pinion thread because like we've both mentioned, and what others on Pirate have mentioned, larger pinion head equates to more contact mesh to the ring gear regardless if it's a standard cut or reverse cut setup.

I've referenced this link also in that same HP Rear Axle thread...

---> TrueHi9 - Gear Page

It's all right there for those who want to read and actually understand it. He even shows how there is more tooth contact with the fatter pinion head. A fat 5.14 Hi9 pinion on a 9" Ford Ring gear has more tooth contact than a HP D60 in 5.13 thus is more stronger.

More tooth contact means more teeth to handle the torque load
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post #38 of 45 Old 11-27-2018, 07:57 AM
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I would not run 37's on a 08 automatic with a stock 3.8. 5.38 gears and 35's would be the set up for a mild trail rig. That tansmission is just bad.
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post #39 of 45 Old 11-27-2018, 09:48 AM
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I'd really like to drive a jeep with 5.13s or 5.38s and 35 just to see no shit how it is...

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post #40 of 45 Old 11-27-2018, 12:21 PM
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I'd really like to drive a jeep with 5.13s or 5.38s and 35 just to see no shit how it is...
Iím just a couple of hours south of you. I know you want to try it with an automatic though.
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post #41 of 45 Old 11-27-2018, 04:41 PM
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I am intrigued. I have been running 4.88s with a manual on 33s, 35s and 37s and I am still looking for more legs on the road. I think I would pull my hair out if I was running 5.38s. Waiting on my 39s to show then I THINK I will be happy on and off road
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post #42 of 45 Old 11-28-2018, 06:08 AM
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I would not run 37's on a 08 automatic with a stock 3.8. 5.38 gears and 35's would be the set up for a mild trail rig. That tansmission is just bad.
I'm at 6 years and 50k miles with 5:38s, 37s and a 3.8L auto. No issues whatsoever. Dropped the trans pan last year for regular maintenance, no ebris in the pan, etc. Secret is keeping it cool. The 3.8L automatics need more cooler capacity. Well documented, easy fix.

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post #43 of 45 Old 11-28-2018, 01:52 PM Thread Starter
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I was thinking about 5:13ís in my 2008 automatic with 35ís. But may be leaning more towards 4:88ís. And putting the 5:13ís in my 2004 with the 5 speed.


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post #44 of 45 Old 11-28-2018, 09:48 PM
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I'd really like to drive a jeep with 5.13s or 5.38s and 35 just to see no shit how it is...
Press the OD/Off button.

Using the rpm charts that you can find everywhere: 3.8 Auto, 3.73, 34" tires (guessing at the measured height of your 35's?), and a .69 OD ratio.

1781 rpm @ 70 3.73, OD On
2581 rpm @ 70 3.73, OD Off ( 2581 / .69 )
2569 rpm @ 70 5.38, OD On

So, by the numbers, pressing that button should give you a decent impression of where you would be with 5.38's. Which, looking at the chart, would be roughly 120 rpm higher than 5.13's. And 5.13's would be about 120rpm higher than 4.88's. By all means find someone with those ratios and drive their jeeps if possible, but in a pinch, od/off...
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post #45 of 45 Old 11-29-2018, 03:35 AM
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Press the OD/Off button.

Using the rpm charts that you can find everywhere: 3.8 Auto, 3.73, 34" tires (guessing at the measured height of your 35's?), and a .69 OD ratio.

1781 rpm @ 70 3.73, OD On
2581 rpm @ 70 3.73, OD Off ( 2581 / .69 )
2569 rpm @ 70 5.38, OD On

So, by the numbers, pressing that button should give you a decent impression of where you would be with 5.38's. Which, looking at the chart, would be roughly 120 rpm higher than 5.13's. And 5.13's would be about 120rpm higher than 4.88's. By all means find someone with those ratios and drive their jeeps if possible, but in a pinch, od/off...
it has become a habit to turn off the overdrive. I start the jeep reach down and turn it off and go on my way. so the jeep runs 70-80 mph down the highway at 2500-3000 rpm as the chart says. The issue is the jeep is slooooow. I know it's not a hotrod and I'm not going to win any stop light to stop light races, but I want it to get out of its own way with a little better, and just have a better performance and driveability.

Do no harm but take NO SHIT
Donut707 is offline  
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