5.38 gears installed with 38’s on 2020 JLUR and this is the second time they blew in the rear

[Jeepjayjeep]

Pinion teeth shearing could be a misalignment issue. That may be possible if they are not installed correctly.

It could also be a fault in the gear sets themselves. A quality control problem with Yukon's supplier may be contributing. A bad run of gears would explain why two sets failed back to back.

How many miles on the gears before they let go?

Noise from the gear set can indicate a problem. Did the shop supply a picture of the gear pattern they should have done as part of the installation?

What is your driving style like? Both during break in and after.

So it looks like both times my gears were done the shop never really explained the break in procedure to me and I drove home for 50 minutes on the highway, no cool down going 120 kms an hour. I didn’t know…. Now paying the hard way…. I have learned a lot reading the forum about the break in procedure, looks like this was the major reason. Thanks to all involved.

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[azwjowner]

So it looks like both times my gears were done the shop never really explained the break in procedure to me and I drove home for 50 minutes on the highway, no cool down going 120 kms an hour. I didn’t know…. Now paying the hard way…. I have learned a lot reading the forum about the break in procedure, looks like this was the major reason. Thanks to all involved.

I would not use that shop again. They should have explained the break in procedure. That they did not is very surprising and makes me question their competence, which would extend to wondering if they also didn't set up the gears well either.

 

[CarbonSteel]

So it looks like both times my gears were done the shop never really explained the break in procedure to me and I drove home for 50 minutes on the highway, no cool down going 120 kms an hour. I didn’t know…. Now paying the hard way…. I have learned a lot reading the forum about the break in procedure, looks like this was the major reason. Thanks to all involved.

Oh wow. Sounds like a $hitty shop not to give you directions on how to break them in.

My process is overkill, but the gears will be broken in without an issue.

Here is another - https://eastcoastgearsupply.com/ft-1479-new-gear-break-in-procedure.html

Note the last line:

PREMATURE OVERLOADING AND IMPROPER BREAK-IN WILL CAUSE GEAR OIL BREAKDOWN AND MAY RESULT IN RING AND PINION FAILURE VOIDING THE GEAR WARRANTY!

 

[2nd 392]

Oh wow. Sounds like a $hitty shop not to give you directions on how to break them in.

My process is overkill, but the gears will be broken in without an issue.

Here is another - https://eastcoastgearsupply.com/ft-1479-new-gear-break-in-procedure.html

Note the last line:

PREMATURE OVERLOADING AND IMPROPER BREAK-IN WILL CAUSE GEAR OIL BREAKDOWN AND MAY RESULT IN RING AND PINION FAILURE VOIDING THE GEAR WARRANTY!

And just ~ $135 per axle eliminates break in heat cycles. Hope he checked your link.

 

[Beachcomber72]

Hi,

5.38 gears installed with 38’s on 2020 JLUR and this is the second time they blew in the rear??? Gears professionally installed by shop and proper break in done, anyone know why??? This is frustrating and expensive! I have seen some posts online about the 5.38 pinion is the smallest and weakest? But another post says it’s not a big difference compadres to the 5.13’s. I don’t know what to do, can’t keep having this happen… should I go to 5.13’s? Jeep runs good when gears are not broken lol.

thanks in advance…

Jason

Goto 4.88 Yukon gears and never look back…

 

[Jeep Dude]

Well if a mechanic said so………. Seriously though, if you’re going to do any kind of hard-core wheeling with 40s, Dana 44s aren’t going to hold up long term.

Clearly.

I somehow seriously doubt though, the OP's self proclaimed heavy foot "on the street", justify the extra costs and weight of a DANA 60, even with 40's on loll.

If the OP was talking about a heavy foot like this below, then this entire conversation would of taken a different turn .

 

[J0E]

Current gen Dana 44, can even handle 40inch dude

Even the mechanic dude agrees, fast forward to 27minutes, 37 seconds.

Or just start here
youtu.be/5Ua7lvwTJ3o?t=1633
See the query string ?t (for time) and the value.

2.0 auto and 4.88 with 38s was great for me. 5.38 seems overkill

There's a bunch of use with 2.0 auto on 38's and 40's with stock 4.10 gears. Everyone screams the sky is falling, it can't work. But mine climbs vertical in M1 at 1,200 RPM, tranny never gets above 200 rock crawling all day in 88 degrees. Not a failure in our group. We don't race light to light.

If you must regear, 4.88 is a better choice, stronger.

Use my bt39.com/GearWheelSpeed to compare gears.

^^^ that is a chart for a JK not a JL (it has been posted here ad nauseum and it is wrong).

What exactly "blew up"? Broken spider gears? Broken ring gear teeth? Broken pinion gear teeth?

bt39.com/GearWheelSpeed is pre loaded for JL, but you can add any rig, even Broco's with 10 speed autos. Doesn't currently support more than a 10 speed.

 

[CarbonSteel]

I have posted this many times here and for the most part, for most people, these are good combinations:

3.6L/ZF8:

33" = 4.56
35" = 4.88
37" = 5.13
38"+ = 5.38

2.0T/ZF8:

33" = 4.10
35" = 4.56
37" = 4.88
38"+ = 5.13

 

[pablo_max3045]

WOW...yep that can get expensive. Are you rock crawling and shock loading it when it blow's, or just more normal driving. 5.38 gears are awful thin for 38's. 4.88's maybe a better option. Plus kind of take it easy on the peddle.
See what some of the other members think.

Even if he was thrashing the shit out of it, the axle should act as the fuse in that circuit normally, no?

 

[Megawatt]

I would stop listening to your installer and find some new shop for gear work.

 

[CarbonSteel]

bt39.com/GearWheelSpeed is pre loaded for JL, but you can add any rig, even Broco's with 10 speed autos. Doesn't currently support more than a 10 speed.

It's pretty darned close--within some tenths of a mile and with an analog speedometer the angle of view could have it off this much.

At 75MPH, I am turning exactly 2500RPMs with a 3.6L/ZF8/5.13/37's (short KO2's):

 

[calemasters]

The 5.38 ratio provides more twisting force. The 38" tires provide more resistance to rotation due to the increased lever arm length (19" lever). I am guessing that the differential can not handle the additional load.

 

[grimmjeeper]

The 5.38 ratio has more twisting force. The 38" tires provide more resistance torotation due to the increased lever arm length (19" lever). I am guessing that the differential can not handle the additional load.

The larger tires provide the same "lever" as you put it no matter what gears are in the differential.

The torsional loads on the differential housing can cause deflection. But that depends entirely on how much force is going in through the pinion and how much traction the tires have, along with how tall the tires are.

The gear ratio does impact the torsional load on the axle shafts and can contribute to deflection and misalignment.

However. Given the description of the behavior, in this case my money is on improper setup or a flawed batch of gears.

 

[CarbonSteel]

However. Given the description of the behavior, in this case my money is on improper setup or a flawed batch of gears.

^^^ this ^^^ in combination with improper break-in sealed their fate...twice.

 

[Maverick909]

yukon has a great video on there gear break in proceedure. 15-20 miles street driving 45mph or less let cool down 20 mins. 15-20 more miles on streets. 20 min cool down. 15-20 miles on the highway. 20 min cooling 3-4x on the highway. THEN if you tow you start back with streets 2x cycles and 3-4x cycles on the highway with towing. Quite the proceedure but it is what it is. The street one isnt bad. basically drive your self nicely to brunch let it cool while eating and drive back home.

I just installed 4.88 Yukons in my JLU its currently geting brake lines installed that where pinched on the first part of break in street run. -_- shop failed to route them correctly. so they are currently installing new replacement lines. cant wait to get the break in procedure done so i can get out and camp. plus ill be running 37's with these 4.88's. feels a like a little much for 35's that i have on the jeep currently

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