Just had my 3rd-gen regeared (4.10 to 4.88 with ARB Front and Rear Lockers), and now there is a constant hum from the front end anytime the transfer case is in 2H (Auto Trans). The noise goes away when the transfer case is 4HI, 4LOW, or N regardless if the engine is running or not. This noise can best be described as what you would hear from oversized mud terrain tires cruising at highway speed although on a lower scale.

The noise starts at approximately 20MPH and can be heard until about 60MPH -- unsure if the sound goes away, or has just been overtaken by road noise. The sound continues through stopping until about 20MPH, and almost sounds akin to a manual transmission vehicle downshifting to use the engine to brake. I am running 265/75/16 Michelin LTX A/T2 tires. Obviously this noise wasn't a factor before the regear, and the tires have never had much noise.

After about 600 miles I started to get a creak/click from the front right. Maybe a bad C/V, and don't necessarily think that it is associated with the re-gear. As for the differentials, I got them from East Coast Gear Supply fully assembled with ARB lockers.

I have been told the cause of the hum is that the axles/drivetrain is always turning and as momentum builds it will eventually transfer to, and turn, the front diff; and that the reason the noise goes away when engaging 4WD is now the diff is engaged and under load. Not a complete novice when it comes to diagnosing mechanical problems, but usually leave the repairs to the pros. At some point my time (and sanity) is worth more then money.

Thoughts, comments?!?! Was ready for the increased RPMs, and engine noise associated with; but this was unexpected and I don't know if it's "normal." Would an improper "shimming" cause this issue? Thanks for any input you can provide.

I answered you in your PM, but I figured I'd post my response also for future readers...

I had a little moan from about 30-33 mph right after my gear install, but it actually turned out to be the tires. I think maybe they rotated my tires for me when they did the gears and they just hummed differently. I don't know, but after a few months, I got new tires and the moan went away.

Since you have a 5 yr. warranty with ECGS, I would probably just wait it out a little while, maybe until your next set of tires and see if the noise goes away. If it gets worse, I'd take both your CVs out, take it for a drive and see if it's quiet, then you know. Just don't go too fast or too far with the CVs out because you could get dirt in the diff. And top it back off with gear oil after you put the CVs back in.

CVs just pop sometimes too. If it starts doing it all the time, I'd think about replacing it/them. Mine pop here and there and I thought one was on the verge of breaking a few months ago, but I've gone 10xs longer on it than I thought I would and it still hasn't broken.

I have noticed some brands of CVs make a little more noise than others too. Maybe you switched them during the R&R and they're rotating the opposite direction than what they got used to before? Just thinking of ideas.. GL!

don't new gears tend to hum for a little bit sometimes until they settle? Call me crazy, but it seems like I've heard that from somewhere. Could be a cv going bad coincidentally.

BTW, nice addition to your 4Runner.

Don't drive the 4runner without the front axes in it. The outer CV joint actually holds the hubs together. If you drive without it, the hub will come out of the knuckle causing catastrophic failure.

As for the noise. What gear oil are you using?

Does the noise go away when you lock your front diff while your in 2wd?

I wouldn't worry about driving with the CVs out if it's just around the neighborhood to diagnose the problem. I wouldn't go off roading or drive it like that more than a mile or 2, but that's the best way to rule out a CV issue IMO and it's fairly quick to do.

I've seen people take a CV out after breaking one just to finish the trail because they didn't have a replacement and didn't want the broken one flopping around. The hub didn't come apart even after several miles of harsh terrain. The bearings are pressed in with like a 20 ton press so I'm sure a light drive around the block won't do anything. I would do it, but that's just me.

Also, did you mark the slip yokes on you driveshafts before you did the R&R?

1. Have to assume the slip marks were marked. I had the install performed by a local shop.

2. As for the gear oil, not sure. Bringing it back in later this week to have the diff fluids changed after 1,000 mile break-in.

3. Yes, the noise is still there when the diffs are locked in 2H.

Thanks for all the replies, please keep 'em coming!

Gear(s) are little tighter than they used to be, nothing wrong with it just will hum, can also be tires associated too. my 2 cents

After you drive it for a while does anything under there get hot.

Maybe try this and you might find the source.

Obviously it it's getting too hot in one area there is a problem there.

yep. my mechanic said the same thing. hubs held together by the cv. never drive without them.

and ontop of that they are the support for your wheel bearings, you WILL crush your wheel bearings if your pull your CVs and drive it, rolling it in and out of your garage is one thing, but driving it around the block is a no no, you are putting a constant load on them at that point and they will have no support, you will hurt your hubs and bearings will fall apart and or damage the whole assembly. every time you turn you would be putting a side load on them(yes even at low speed, like 5mph) and their would be no support or anything holding them in/together. just save yourself the trouble and dont try this.
id say wait it out see if the noise gets worse or goes away. also you will need to flush your diff fluids in about 500miles so see if that helps.

Ahh, you guys are being overly cautious. You're treating these hubs like delicate flowers when they take 40,000 lbs to press a wheel bearing out. I've seen these hubs get absolutely beat on without CVs and no issues. I understand your concern in theory, but they are way stronger than you give them credit for. A quick drive around the block taking it easy on the turns wouldn't do jack. I know this to be true, but if you'd rather pay someone to diagnose a problem that you could do yourself in an hour in your driveway, go for it. Like I said, I'd do it, but that's up to you.

I totally agree it's not a good idea to drive like that, but I'm just saying go in a straight line, get up to 20-30 and see if the noise is there and stop and put em back in.

too be honest some gears are just louder then others, or need a bit of time to settle, if you think your shop did a good install, keep rolling it for a while then check the gear oil for smell,color and grit. just make sure you do this before you go past the shops warranty mark, also checking the diff for heat is a good idea as well get one of those laser themro's from harbor freight for like $30 and give it a wack. either way either the shop screwed up or they didn't and you have a good install and the gears are just loud or something else is going on.
at this point i'd just say run it for a while and give it a check, not much you can do really with out ripping back into it to have a look.

also some ratios are louder then others as well, in my jeep the 4.56's are quite a bit louder then the 4.88's , it may just be something you have to deal with.

I have used a 5 ton puller and pushed the hubs out by hand. I know that if you loosen your hub nut, and drive on the road, you will hearing a roaring bearing noise. It is what is.

Why do you think toyota FSM says to torque the hub nut to 215 ft pounds?

The bearing is a double roller bearing using two tapered bearings. If you have the vehicles weight sitting on those two ramps, it is only natural for the weight to push the ramps apart.

They probably had manual hubs and not add hubs. You can do this with a manual hub but I wouldnt try it with an add hub. I think you are confusing the two