Re-gear break-in for front differential

Window&DoorWhore

Window&DoorWhore

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So just got the Jeep back from the shop yesterday after the 5.13s were put in. Guy wants it back in 500 miles for a fluid change and inspect wear pattern. Went through a few heat cycles yesterday and took it on the free today for the first time. Turns out I’ve got that highway rhythmic vibration that you only hear about after dropping 2500 on gears and an Eaton LSD.. so looks like I’ll run it without front shaft and have it balanced and ultimately bend over for a manual hub kit.

Is what it is. I like the idea of locking hubs anyway. Just thought I was done spending money on it for a while. Pulling driveshafts for diagnosis brings me to another question. If he wants it back in 500 miles to check wear pattern and change gear lube, does that mean I should remove the rear shaft after 500 and let the front pull me around for another 500?

Driving around town in 2hi for a break in, might as well be flat towing the Jeep those 500 miles as far as the front diff is concerned since the ring and pinion Up front is only making contact on its coasting surfaces.

Thoughts? Is there anything I should be concerned about going full time front wheel drive for that long?
 
I called the tech line at Revolution and they did not sound too concerned about front gears. He did say to put a few cycles in 4wd just like the rears to give the front a little break in time.
 
The cyclical vibration may be caused by a bad driveshaft U joint.
Do an inspection of the U joints to see if there is indications of rust around the U joint cups or a joint cup spinning inside the yoke ears.
 
CharlesHS said:
The cyclical vibration may be caused by a bad driveshaft U joint.
Do an inspection of the U joints to see if there is indications of rust around the U joint cups or a joint cup spinning inside the yoke ears.
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I’d love it if that’s the case. The front appears to be stock, the rear shaft has what I think is a slip yoke eliminator and a double u joint off the t case. As far as seeing anything, it’s all been painted before I bought it so I guess the only way to tell is to remove the shafts and check individual movement of the joints.
 
Couldn’t you just drive it in 4wd if you want a load on the front diff? I don’t think I’d bother removing the rear for break in purposes but that’s just me. Interested to know if there is a need for it.
 
Window&DoorWhore said:
Turns out I’ve got that highway rhythmic vibration that you only hear about after dropping 2500 on gears and an Eaton LSD.
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It's too bad nobody warned you in advance. Don't waste too much money on a fix other than the hubs. The front gears don't do much other than spin most of the time. They don't need special treatment and don't drive on the road in 4wd to break them in.
 
I want to re gear mine with 5.13s. I have heard about this vibration issue. Is it common? Also, is it in the front end? How bad is it? Harmless if left alone?
 
Rubicon John said:
I want to re gear mine with 5.13s. I have heard about this vibration issue. Is it common? Also, is it in the front end? How bad is it? Harmless if left alone?
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Not common but something that does happen and if it does it ends up costing more than the re-gear to fix. It is worth mentioning so people know what they are getting into. Most people that have the issue are not happy leaving it alone.

(@Chris has a thread dedicated to the issue somewhere)
 
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Thank you guys. It honestly kind of sucks. The re gear itself isn’t cheap. And I know the 5.13s are a better choice for me than the 4.88s
 
Rubicon John said:
Thank you guys. It honestly kind of sucks. The re gear itself isn’t cheap. And I know the 5.13s are a better choice for me than the 4.88s
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If you have 33’s then you want 5.13, anything else and you’ll have your finger on the OD off button every time you drive. Not everyone gets bad vibes going to deep gears but the ones that do are vocal about it.
 
Window&DoorWhore said:
If you have 33’s then you want 5.13, anything else and you’ll have your finger on the OD off button every time you drive. Not everyone gets bad vibes going to deep gears but the ones that do are vocal about it.
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Yeah I’ve read up a lot on the re gear itself. I just worry about these vibrations that people are experiencing randomly.
 
I know this is an old thread, found it a few days ago and wandered off to the "Vibrations after re-gear" thread but rediscovered this in a search for the original topic, "Re-gear break-in for front differential".

FWIW I asked my installer that question yesterday. 500 miles is the standard but what about the front. Just no 'wheelin' is what he said until 500 miles, 250 should be good but the more the better". Kind of a stumper. Gonna take awhile to get 500 'offroad' miles on.

Gonna drive it around in 4-Hi every chance I get off pavement, or in anything loose or slightly slippery I guess. That's the only thing I can come up with. Seems to be no definitive answer to the OP question. But lots of folks have done the re-gear and are running around just fine.

And yes, I got the 5.13/35s/65mph pulsating vibration with the 6spd. Have yet to dive into that but knowing it's not critical - will get to it.
 
The front doesn't do much. Most people just break in the rear and let the front go along for the ride and front failures are few and far between from break in issues. Heat is the main problem and it would be really surprising if you got much heat in the front diff even on a pretty difficult trail. If you are remotely concerned stop after 10 minutes on the trail and feel the front diff. You're supposed to do a similar thing when you tow for the first time on new gears even if you have completed the normal break in.
 
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pagrey said:
The front doesn't do much. Most people just break in the rear and let the front go along for the ride and front failures are few and far between from break in issues. Heat is the main problem and it would be really surprising if you got much heat in the front diff even on a pretty difficult trail. If you are remotely concerned stop after 10 minutes on the trail and feel the front diff. You're supposed to do a similar thing when you tow for the first time on new gears even if you have completed the normal break in.
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Miles and miles of dirt roads out here with some snow pack so should be easy enuf to run in 4WD cycling in cool off periods.

Have a trail run Saturday with the local group but gonna drive the XJ since I'm not sure if we'll be bucking crusty snow drifts or mud with temps in the high 40s F, and sure don't wanna hammer down locked up or such. The XJs done that a ton of times.
Gonna get some grief from my buddies for leaving the new TJUR in the shop...
 
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I might have posted this a few times but a cheap temp gun really lets you see when they are done cooking. The initial heat and drop as they break in is very obvious each run. I didn't really see any change in the front on mine on the trail or on the highway after the first 10 miles. They were just slightly warm the first drive and that's it.
 
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