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Unread 02-06-2010, 05:31 PM   #1
sherlocktk
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1984 CJ7 
 
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Location: Lake Forest, CA
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100 Miles new gears, Now Noises

I fished new gears about 3 weeks ago. First 5 or so break in miles ok, then I started to get a weird vibtation from 40-60 mph. Sounded like a unbalnaced drive shaft or something.

Drove it again next day and since then the vibration has been only 40-45 miles per hour, any faster and its perfet or slower and its fine too, so basically just that range. I have had it up to maybe 70 or so. 4.56 gears

Start lookiong into it more today (after maybe 100 miles, of city driving on the gears, no more than 5 miles at a time)

Backlash Increased from .008 to .014-.015. Also the pinion pre-load was set at 25 in lbs and now its less than that, Before it was harder to turn by hand with nothing, and now with the carrier it is significantly easier. I cant measure yet as I have not taken it alll apart. When I set it all up markings were good etc, Im just suprised at the amount of wear in a short time frame. When I took the stock one out with 170000 backlash was .016.

If vehicle is on jackstands, no gear lube, except what is left on carrier, no tires it makes a god awful noise once you hit 20 mph (4th gear idle) Sounds like playing cards in bicycle spokes, but the cards being metal

Could this be causing the vibration. Should I move the gears back in to .008

Front gear set (done at same time) seems to be doing just fine, no noises from that one at all. Gears and install kit were superior axle and gear.

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Unread 02-06-2010, 11:18 PM   #2
73CJMN
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Did you set the pinion depth? What does the wear pattern look like? How much preload did you put on the carrier bearings? New bearings? Could be any one of those or combination. The change in backlash is a dead giveaway something not right.
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Unread 02-07-2010, 12:23 AM   #3
sherlocktk
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New bearings all the way around. (pinion, carrier, and outter axle bearing) Pinion depth set to make pattern look good.

What IM thinking now is all the "grit" that got on the shims effected the preload when I put the carrier in and that made everything a little loose. Once I took the caps off the carrier just fell out, so it has to be that. as of now I added .013 to the left side to decrease backlash, (and preload) and its looking at .007 as of now, so im going to tighten it all back up. Any tighter than that I dont think I can get it in there.

As far as pinion preload Im thinking to make sure its at least 5 in lbs and call it good as that is spec for "used"
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Unread 02-07-2010, 02:05 AM   #4
80cj
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Assuming you set the gears up properly, the vibration could be coming from U joint angles. I would check there first. Remember that with the 4.56 gears, the drive shaft is turning faster. If you put a vehicle up on jackstands and run it in gear, yes, you will hear some scary noises. I did that to mine not long after changing axles and gears . What you're hearing is alll the back lash in gears- transmission, transfer case, rearend gears, axle splines, etc. because the drive train is unloaded. The sounds will be worse if you have a slightly warped brake drum as it will tend to load and unload the drive train as it turns.

If you suspect gears, listen for changes in sounds going drive to coast in 4th gear. There should not be a significant change. Improperly set gears will make a whining or growling sound usually on coast conditions when you release the gas. Several years ago my friend had new gears installed in his 83 J10 truck. about 10K miles later he asked me to install a Detroit in the rearend. Before pulling things apart, I measured the backlash, It was at .013 or so. I am assuming the shop that set the gears had set it in the factory range (.007-.010) on setup. When he sold the truck last year, it was still running quietly (the gears, the Detroit had it's usual clunks and bangs).

Yes, pinion preload will loosen but how much, I don't know. Just make sure you can't shake it up and down/in and out. I set up 4.56's in a friends YJ a few years ago. Two years later, he wanted to change to 4.88's which I did for him again. There was less than 4000 miles on the Jeep since installation of the 4.56's. I was surprised at how easy it was to turn the pinion. It was like it had lost a lot it's preload but everything turned smoothly with no slop or play.

Last edited by 80cj; 02-07-2010 at 02:38 AM..
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Unread 02-07-2010, 05:37 PM   #5
JeepHammer
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Turn your pinion back and forth with the trans or transfer in neutral...
Can you detect any side to side play in the pinion shaft?

Does the pinion walk in and out as it's rotated back and forth?
If so, you wiped out the pinion bearings.

If the pinion moves, you have REAL ISSUES, and you need to address that problem FIRST & IMMEDIATELY!


Having gear lash open up after driving a ways is common for someone that doesn't know you have to pry the carrier over before you tighten caps down.
You will need to pull carrier bearings and re-shim to get your gear lash back...

Make sure your wear pattern is in the correct spot before you worry about side shims...
Pinion set first for tooth wear pattern, then worry about side shims since you can't reset the pinion after the carrier is in.
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Unread 02-07-2010, 08:12 PM   #6
sherlocktk
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An Update

Pinion is still perfectly tight and has 8-9in lbs of rotating force. This seemed acceptable to me. I could not wiggle it at all, and it rotates smoothly and freely. No driveshaft attached so I can feel it good.

Im pretty sure I just did not pre-load the carrier enough. It seemed tight when I put it in a month ago. Everywhere I read was a few whacks from a dead blow hammer. I could not pull it out without prybars then. Now I cant even pull out with a prybar, and have to use the rag against ring gear and pinion to get it out. My gear pattern still looks good, so Im not too worried.


Thx for the help. After I get it buttoned back up (tuesday) ill post an update to let everyonne know how it went.
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Unread 02-07-2010, 10:07 PM   #7
80cj
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Quote:
Originally Posted by sherlocktk View Post
An Update

Pinion is still perfectly tight and has 8-9in lbs of rotating force. This seemed acceptable to me. I could not wiggle it at all, and it rotates smoothly and freely. No driveshaft attached so I can feel it good.

Im pretty sure I just did not pre-load the carrier enough. It seemed tight when I put it in a month ago. Everywhere I read was a few whacks from a dead blow hammer. I could not pull it out without prybars then. Now I cant even pull out with a prybar, and have to use the rag against ring gear and pinion to get it out. My gear pattern still looks good, so Im not too worried.


Thx for the help. After I get it buttoned back up (tuesday) ill post an update to let everyonne know how it went.
The diff carrier bearing preload spec for an AMC 20 is Zero end play plus .008",
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