Is gear noise a time bomb?

I just swapped in a HP30 axle that has 4.56 gears and a LockRight. I am currently running without a front driveshaft since the rear is still 3.55. When first driving the jeep, there is no noise. When I get up to highway speed and then slow down (like on the offramp) I have a very noticeable noise coming from the front diff. As I slow down, the noise starts somewhere between 30 - 40mph and from then on I hear the noise constanly when driving at that speed or less. I'm using Mobil 1 synthetic gear lube which is a 75-90 weight. The previous owner did not have these noises so I'm thinking maybe I did something to it when I removed the carrier to inspect the axle seals. But I am sure I put everything back in the way it came out.

I can live with the noise but I am worried that the diff might grenade on me sometime in the future. Is gear noise a sure sign of iminent failure?

I also was planning on doing a manual hub conversion later in the year or next winter. Ideally if I could do this now, the gear issue would not be an issue on the street and wheeling is at slow speeds, so would I still need to be concerned about this? (diff grenading on the trail, is just as bad ($$$) as if it grenades on the street...)

Any advice would be much appreciated.

Are you sure its your diff that's making the noise? I guess if you haven't touched anything else it certainly could be, but I wonder because when my passenger brake pads are worn the vibration/noise that comes out seems to be coming from the diff.... Just a thought.

Yes I am sure. I also hear the LockRight making slight ratchetting sounds when turning, but from what I am told that is to be expected. Both noises are coming from the same locale. Even though I have never had gear noise before, this sounds exactly how I would imagine gear noise to be. Everything else is tight.

open up the cover and take a look for anything obvious like bearings. heck, run a pattern and see what you've got. could be excessive backlash in your gearset(check it with a dial indicator if you have access to one)...maybe you swapped bearing races when you pulled it out, or bearing caps. everything's gotta be right because the tolerances are tight.

xjblaine said:

open up the cover and take a look for anything obvious like bearings. heck, run a pattern and see what you've got. could be excessive backlash in your gearset(check it with a dial indicator if you have access to one)...maybe you swapped bearing races when you pulled it out, or bearing caps. everything's gotta be right because the tolerances are tight.

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Checking the backlash and pattern is definitely beyond my know-how...

I'm sure I got the bearing races on the right sides, and matched up the letter stamped on them...

But I was reading the FSM and it describes what I have as either incorrect backlash or possibly the carrier bearings. Can I buy new bearings at say NAPA and replace those hoping this was the problem... What if I waited until next Monday to open the cover to inspect the fluid for shavings and I could do the new bearings then, but boy that would suck (have to pull the shafts again...)

Some other random thoughts...

I cleaned the insides with brake parts cleaner - you know, spayed it around real good. But it would have had time to dry since it aired out and I didn't fill it till the morning after installing the cover again. Could the brake parts cleaner gotten into the bearings and done them harm?

Also FYI, after driving a couple times, I got out and felt the diff cover and housing with my hand to check if it was hot and it was not hot at all...

Do you have a digital camera. DO a pattern check and snap some pics. We can help you diagnose the trouble better. Also, beraing caps are different from bearing races. Bearing caps hold the carrier in and are stamp like you mentioned. The bearing races are the shinny ends on the carrier bearings.

If your carrier bearing are bad, you can buy a mini kit for about $25. You will still have to set your backlash and check your pattern. This is the easier part of a gear install. I think you can do it, it may take 1 full day but you can do it.

A for tools, buy or borrow a good dial caliper, dial indicator and stand. You'll need a bearing separator and puller and a brass punch. most can be found at habor frieght, for about $50 for everything.

Otherwsie you last resort is finding a gear guy who may only chage you $50 for his time. If the job is an easy one.

Well I took it to the best driveline shop in town for a test drive and the guy didn't think I need to worry about it too much. It doesn't sound good but he said it may just be noise from the gears free spinning because the driveshaft is removed. I realize that even with the driveshaft on, it would still spin not under load but he said I shouldn't worry about it until I get the front driveshaft back on. Thats good. It may still be a diff bearing however. To make sure its not damaging the gears I am going to pull the cover again, and check the fluid for metal. After driving it 100 miles like this, there should definitely be metal shavings in the fluid if it is a gear problem.

This is not bearings.

I think I know what happened. There were probably two LARGE shims on each side of the carrier, outboard of the bearings. You probably switched those, and now you have very excessive backlash. I do not think this is a bearing question at all, get some bluing and run a patttern, the FSM has pattern descriptions in it and we can help. don't throw money at the problem if it was fine before you go in there. Don't be afraid of gears, it's really quite easy.

EricsXJ said:

Well I took it to the best driveline shop in town for a test drive and the guy didn't think I need to worry about it too much. It doesn't sound good but he said it may just be noise from the gears free spinning because the driveshaft is removed. I realize that even with the driveshaft on, it would still spin not under load but he said I shouldn't worry about it until I get the front driveshaft back on. Thats good. It may still be a diff bearing however. To make sure its not damaging the gears I am going to pull the cover again, and check the fluid for metal. After driving it 100 miles like this, there should definitely be metal shavings in the fluid if it is a gear problem.

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Why didn't the guy want to take a pattern, is he too lazy or was it going to charge you for his time?

xjblaine said:

This is not bearings.

I think I know what happened. There were probably two LARGE shims on each side of the carrier, outboard of the bearings. You probably switched those, and now you have very excessive backlash. I do not think this is a bearing question at all, get some bluing and run a patttern, the FSM has pattern descriptions in it and we can help. don't throw money at the problem if it was fine before you go in there. Don't be afraid of gears, it's really quite easy.

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What shims are you talking about? the bearing races, all the shims are between the carrier and the bearings.

ChuckD said:

Why didn't the guy want to take a pattern, is he too lazy or was it going to charge you for his time?

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The test drive was free of charge. After hearing it he didn't think it was the gears (without being able to hear it under load) If I wanted, I am sure they would've taken my money if I asked them to work on it, but if its not the gears, that would be a waste of money also (gear work is not cheap, and these guys are the best shop in town which also means they charge more) Instead, I'll pull the cover tomorrow and inspect the fluid and go from there.

outboard of the bearings (sorry, I forgot this earlier) there may be two 'shims' that go between the bearing race and the axle housing. I'd bet money that you accidentally switched these. Open it up and look to see if you have these spacers lemme try and show you. 'll' is the housing, 'i' are the spacers I think you swapped, 'o'are the bearings, and 'C' is the carrier....

llioCoill

kinda see what I mean? Dont spend any money on this until you are positive you didn't change anything. It would be a HUGE waste to pay the labor for this.

xjblaine said:

outboard of the bearings (sorry, I forgot this earlier) there may be two 'shims' that go between the bearing race and the axle housing. I'd bet money that you accidentally switched these. Open it up and look to see if you have these spacers lemme try and show you. 'll' is the housing, 'i' are the spacers I think you swapped, 'o'are the bearings, and 'C' is the carrier....

llioCoill

kinda see what I mean? Dont spend any money on this until you are positive you didn't change anything. It would be a HUGE waste to pay the labor for this.

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Are you sure you are talking about a HP D30? Where in the FSM does it show these shims? The shims i know will not fall out pf the carrier if it is pulled out. They are between the carrier and bearings, some will adjust the backlash that way, but then they go between the carrier and bearings.

xjblaine said:

outboard of the bearings (sorry, I forgot this earlier) there may be two 'shims' that go between the bearing race and the axle housing. I'd bet money that you accidentally switched these. Open it up and look to see if you have these spacers lemme try and show you. 'll' is the housing, 'i' are the spacers I think you swapped, 'o'are the bearings, and 'C' is the carrier....

llioCoill

kinda see what I mean? Dont spend any money on this until you are positive you didn't change anything. It would be a HUGE waste to pay the labor for this.

Click to expand...

There were no spacers or shims between the housing and bearings, I am sure of that.

Well I pulled the cover. The fluid has a very small amount of metal specs in it and a tiny number of larger peices that I would describe as a sliver. But not a lot by any means. I had about the same amount when I changed the fluid for the first time on my stock axle (albeit that was at 24,000 miles...) Rotating the pinion by hand feels smooth. Keep in mind this was driven 100 miles much of it on the highway...

I called the guy back that did the test drive and he said it is pretty cut and dry now - install the front driveshaft to load it and if the noise goes away I'm fine. If it continues I have a problem. So here is what I'm going to do - I bought some heavier weight oil 85-140 to see if that would make a difference. I'll first run it the same as before but see if the sound changes at all with the heavier oil. Then I'll remove the rear driveshaft and install the front. This will be interesting with the locker, but I will be able to tell if the noise continues or not. If the noise continues and/or gets worse, I'll take it in for service. If the noise is still there but not as bad, I may just get the hub conversion now and leave it as is. If the noise completely disappears, I should be good to go as it is.

How does this sound?

Do you stil have to cover off? If so, get some grease if you can't get any gear marking compound and do a pattern check. Yukon and others out there have published there instructions. Compare the pattern and see for yourself.

Otherwise your wasting your time. A warn kit would be a good mod overall, but not a cure for noisey gears.


Just my Opinion.

ChuckD said:

Are you sure you are talking about a HP D30? Where in the FSM does it show these shims? The shims i know will not fall out pf the carrier if it is pulled out. They are between the carrier and bearings, some will adjust the backlash that way, but then they go between the carrier and bearings.

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They were not listed in the FSM. My hpd30 did not have these (I don't know if others would), but my d35 and my friend's 12 bolt did, they were different thicknesses, and it was really hard to tell but they were a few thousandths off by the micrometer. Eric, if you had no noise untill you messed around with the carrier, than something must not have been put back the same way. If you have the cover off, hold the pinion in place while you wiggle the ring gear. You should feel very little movement and get a quiet click as you wiggle the ring back and forth. If it's alot of movement, it's a backlash issue. I would focus on this before getting a hub kit, you'll still have something wrong in there.....

xjblaine said:

...Eric, if you had no noise untill you messed around with the carrier, than something must not have been put back the same way...

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See thats just it - I've never used this axle before now. I removed the carrier prior to swapping the axle in. There was also welding done to it too, extended swaybar mounts and miniskids. Maybe that slight amount could have warped it ever so slightly???

Anyways, I just ran it with 80-140 weight oil and the noise is nearly indecernable. I don't like that though because it may be masking the problem. Next step is connect the front driveshaft and see if the noise changes.

Either way I think I need to come to grips with the fact the gears should be reset professionally. The ring and pinion are OK at this point but maybe not after 1,000 miles or so...

Update: drove it front wheel drive and there's definitely a problem. Looks like I'll be out $300 - $400

you should find someone locally to help you with this. 3-400 is a LOT of money for something that can be done in a driveway with the proper tools in an hour, better yet, find a cheaper install place, around here they do $150 with the azvjc club discount. Otherwise, you're wasting your money. good luck.