Gear swap ? - : Jeep Wrangler JK Forum
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post #1 of 7 Old 09-05-2010, 12:35 PM Thread Starter
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Gear swap ?

Guy's I just had 4.88's installed in my 2 door x. When i reach 40-45 mph I hear a sound/vibration. I noticed this after I put my top and doors back on. I haven't driven it for the 500 break in miles yet. What are your thoughts???

Last edited by bananaclip; 09-05-2010 at 01:36 PM.
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post #2 of 7 Old 09-05-2010, 01:07 PM
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sounds like the top is flapping. There is a velcro enclosure about half way back on the soft top. make sure that is wrapped around the metal bar and secured.

I have a jeep and it goes over shit.
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post #3 of 7 Old 09-05-2010, 01:35 PM Thread Starter
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Defiantly not the top. It is more like a driveline vibe.???? My JK has the tera leveling kit and I am running 305 75r 16 km2's. I never had this vibe/rumble before the gear swap???
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post #4 of 7 Old 09-05-2010, 02:30 PM
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I am by NO means a mechanic... but, I have a 2 door, auto, and just did a ring / pinion gear change and added Spartan Lockers. I went with Yukon Gears, and my brother did the install for me. He, on the other hand IS a mechanic by profession.

Here is what I learned, watching him. First, he checked the factory backlash on my factory ring and pinion gears. My jeep only had about 16K miles on it when I did the gear swap. (I went to 4.88:1).

When he installed my new gears, he took the time to make some set up bearings out of my old pinion bearings. Basically, he honed the old pinion bearing to a slip fit, so he could take the pinion in and out, to measure the pinion depth, to make sure the gear mesh was spot on, and the backlash was within specs.

I drove the Jeep for a few miles to get the gears up to temp and then went through a cooling cycle. I did this four times, at about 25 miles a pop, before I drove it any distance.

I just dropped the covers yesterday, and changed the gear oil, checked backlash / gear mesh again, and they were spot on.

In fact, my Jeep rides BETTER now than it did factory... and the Yukon gears are VERY quiet. In fact, the lockers are WAY more quiet than I had imagined, since I had never run a lunchbox style locker before.

I'm very happy with the way it turned out.

If something is vibrating, or whining, I would take it back to who did your gear install. Just going on my own experience, it should not be making any noises.

2010 JK Sport: 4.88:1 Yukon Gears, Spartan Lockers, A.C.E. Rock Rails, Gobi Stealth Rack, HELLA FF75 lights, 16x8 ION ALLOY 174 wheels, 315/75/16 Maxxis Bighorn MT's, Smitty XRC front bumper, Smitty XRC8 winch and cover, Smitty roller fairlead license plate holder, Alpine Sound System with JL Audio Sub, 2.5" Rock Krawler Stock Mod lift, Bilstein 5100 shocks, Bedlined front Grille
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post #5 of 7 Old 09-05-2010, 04:41 PM
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I have a 2005 Jeep LJ and have the same vibration. I hear that its a characteristic of 4.88 gears.


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post #6 of 7 Old 09-05-2010, 05:11 PM
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Was anything else done recently? Lift? New driveshaft? New tires? Did a wheel weight fall off?

What kind of noise?

This is from Randy's R&P, and may help:

What is this whirring noise?
Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.

A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.

Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.

Regular clunking every few feet may indicate broken ring or pinion gears.

Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.

Rumble while turning may indicate bad wheel bearings.

A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.

Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts.

When I installed my gear set it was quiet, but it's getting loud with time. What happened?
It is most likely a result of the gear not being broken in properly or driven "too hard, too soon." When this happens, the gear oil breaks down and the resulting temperature inside the differential causes the face of the gear to wear away exposing the softer metal underneath. When this happens the gear will wear down more and more until the gear completely fails.

Last edited by GreenJK; 09-05-2010 at 05:49 PM.
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post #7 of 7 Old 09-05-2010, 06:53 PM
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Just had mine done

I just did a gear swap on my 08 unlimited going from the stock 3.73 to the 4.88 gears. Before I did the install I checked out probably 5 or 6 shops before I found one that I felt comfortable doing the install. The shop that did mine specializes in Jeeps and as of right now I have about 200 miles on the gears without any whine, noise or vibration. I am following the break in period to the letter and according to the shop instructions.

With all this being said It sounds like the installation of the gears weren't done right, there is no reason you should have any noise much less vibration.
Your going to need to pull the diff cover off and see whats going on inside.....

good luck

Oh and by the way I love my 4.88's they rpm just where I need them on the street.

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