New 4.56 gears and now noise and vibration


DGJ

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Hello, I am a new member but have been visiting this site for months learning about my TJ. This is an awesome forum. I have a 2004 X model with 4.0 and 5 speed manual. I plan to move up to 33" tires so I had it re-geared from 3.07 to 4.56 by a local offroad shop. The shop did 2 heat cycles on the gears prior to me picking up the vehicle to ensure the break-in process was done correctly. As I drove away I noticed a hum beginning at about 45mph that got progressively worse the faster I would go (seamed to come from rear diff). I kept the jeep below 55mph hoping things would smooth out. After about 20 miles I ran it up to 60mph and the sound was significantly louder and I could feel it through my seat and it was resonating inside the jeep. The noise would increase with speed but not really impacted by acceleration or pushing in the clutch. I pulled over and the rear diff was very hot to the touch. I sat for about 20 minutes to let it cool a then limped back to the shop using back roads keeping my speed below 45. Upon arrival they used an infrared thermometer and the rear diff was 185 degrees. They didnt seem too concerned but said they would look into it. The shop did mention they had an issue pressing on the pinion bearing. Apparently they had to order a second bearing as they were never able get the first one to fit. The shop is a Yukon certified installer and used Yukon gears. I am concerned because the cost of the regear was not cheap. Any insight or wisdom I can possibly share with the shop is greatly appreciated. Thank you.
 

Jerry Bransford

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Regearing is not a simple process and even very experienced R&P installers with good reputations occasionally botch a job up which happened to me many years ago. My bet is your installation did not go well. Did the installing shop at least know to use a conventional gear lube, not a synthetic, during the break-in process for the before and after the first gear lube change? The gears will run significantly hotter if lubed with a synthetic during the break-in.
 

Trevlaw

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X2 on checking the rear driveshaft.

Also, do you know specifically what the shop did for the break in process? Usually it's recommended to take it easy for a few hundred miles. If they just ran it on a lift I don't think that would be sufficient vs actual on road driving.
 
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DGJ

DGJ

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Conventional gear lube was used (shop owner verified). They ran the jeep around town 10-15 miles going easy and avoiding highway speeds....let it cool completely then repeated the process. I also babied it when I picked it up.

We did not discuss possible driveshaft issues but I will bring that up. No noise or vibration prior to the regear. U-joints are spicer and about 3 months old. The jeep has not been offroad.

The sound is best described as a buzzing grinding noise that you can hear and also feel. The sound and feel increase with speed. I never exceeded 63 mph (gps) which was when I decided to stop and return to the shop.
 
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Jerry Bransford

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Conventional gear lube was used (shop owner verified). They ran the jeep around town 10-15 miles going easy and avoiding highway speeds....let it cool completely then repeated the process. I also babied it when I picked it up.

We did not discuss possible driveshaft issues but I will bring that up. No noise or vibration prior to the regear. U-joints are spicer and about 3 months old. The jeep has not been offroad.

The sound is best described as a buzzing grinding noise that you can hear and also feel. The sound and feel increase with speed. I never exceeded 63 mph (gps) which was when I decided to stop and return to the shop.
My bet is the rear gears are toast.
 
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DGJ

DGJ

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Jerry - I sure hope not. They probably wont get to open it back up until Monday. The shop owner seems like good people so I think he will make it right.

Bob - Right now the jeep has a set of BFG 31x10.50's. The 4.56 gears are a little too deep for the worn 31's. I think it is going to be perfect once I get the 33's on it.
 

freedom_in_4low

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Hello, I am a new member but have been visiting this site for months learning about my TJ. This is an awesome forum. I have a 2004 X model with 4.0 and 5 speed manual. I plan to move up to 33" tires so I had it re-geared from 3.07 to 4.56 by a local offroad shop. The shop did 2 heat cycles on the gears prior to me picking up the vehicle to ensure the break-in process was done correctly. As I drove away I noticed a hum beginning at about 45mph that got progressively worse the faster I would go (seamed to come from rear diff). I kept the jeep below 55mph hoping things would smooth out. After about 20 miles I ran it up to 60mph and the sound was significantly louder and I could feel it through my seat and it was resonating inside the jeep. The noise would increase with speed but not really impacted by acceleration or pushing in the clutch. I pulled over and the rear diff was very hot to the touch. I sat for about 20 minutes to let it cool a then limped back to the shop using back roads keeping my speed below 45. Upon arrival they used an infrared thermometer and the rear diff was 185 degrees. They didnt seem too concerned but said they would look into it. The shop did mention they had an issue pressing on the pinion bearing. Apparently they had to order a second bearing as they were never able get the first one to fit. The shop is a Yukon certified installer and used Yukon gears. I am concerned because the cost of the regear was not cheap. Any insight or wisdom I can possibly share with the shop is greatly appreciated. Thank you.
Does the hum change in pitch with speed or does it just get louder/more intense? Increasing pitch usually points to gears, constant pitch but increasing volume points to pinion bearing.
 

Trevlaw

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If you're able to safely put it on jackstands and run the rear axle at idle speed, should be pretty easy to tell with a mechanics stethoscope. My bet is on gears or bearings
 
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DGJ

DGJ

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Freedom 4Low- Pitch does not change...just seems to intensify with vehicle speed. Acceleration or deceleration does not seem to matter. Even coasting with the clutch in the buzz intensity correlates to vehicle speed. Better described as a buzz than vibration.
There were issues with the pinion bearing during install. That might be the culprit.
 
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Regearing is not a simple process and even very experienced R&P installers with good reputations occasionally botch a job up which happened to me many years ago. My bet is your installation did not go well. Did the installing shop at least know to use a conventional gear lube, not a synthetic, during the break-in process for the before and after the first gear lube change? The gears will run significantly hotter if lubed with a synthetic during the break-in.
Yea I’m goin with improper installation,just rehearing shouldn’t lead to vibration
 

freedom_in_4low

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It's possible an out of balance driveshaft can show itself after a regear when you're getting into previously unreached driveshaft speeds, but with these showing up at 45 you would have had them at 66 before the regear. I also would characterize that as more of a vibration rather than a grind, as this was described.
 

JMT

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Thanks 4lo. I hope to hear something from the shop Monday.
Who did your gears, if you don’t mind me asking? I had mine done in Austin at Just Jeeps.
 
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DGJ

DGJ

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I didnt call Just Jeeps. Probably should have checked around a little. I paid $1700. Yukon Gears and new carriers.
 

JMT

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I didnt call Just Jeeps. Probably should have checked around a little. I paid $1700. Yukon Gears and new carriers.
As a Yukon dealer who used Yukon gears, they should make this right. Your description of steady increasing buzz or vibe sounds more like gears to me than driveline/pinion issues. Further, this is all you’ve had changed. Of course, the shaft is turning faster, and balance could be an issue, but rear gear setup seems to be the culprit IMHO.