Hi guys,
The title is pretty much self explanatory. Yesterday my 1998 4runner started making a pretty loud humming noise when decelerating in 4x4.
Happens in both 4Hi and 4 Low. Faster speeds make it louder. No noise when in 2WD or when accelerating in 4wd.


Im thinking its a bad pinion bearing in the front diff. Could it be anything else?


I don't have any experience rebuilding diffs.. How difficult would it be to do myself? I have a press and bearing splitter/puller. I heard that replacing pinion bearings is much easier than side bearings.
How much time would it take a professional to do the job, if I bring him the differential and the parts?
Thanks!

 

They all make a bit of audible noise in 4x4 and more so with the centre diff lock and even more so in cold weather, even our brand new 2012 Taco. I would start with a synthetic proper spec gear oil, inspect the fluid drained for chunks and call it good unless you can still hear it with the heater fan on. I run April full syn 75W90 in the diffs and tcase works fine at -40*C today and makes a bit of acceptable noise if I shut off the heat and stereo. It is advised to engage the 4x4 every month to lubricant everything.

 

The noise is certainly WAY louder than what anyone would consider normal or acceptable. You can hear it very loud and clear with both heater and stereo on.. There is definitely a problem there. The oil in the diff is (Amsoil severe gear 75W90) is 5 months old.


The differential has 350k km (~200k miles) on it with unknown maintenance history. I swapped it in this past summer along with the rear when I upgraded to e-locker and 4.56 gears.

 

Are you using your 4 wheel drive on hard surface dry road??

Cooler temps can make all kinds of interesting noises

Tire noise on roads one would pay no mind to when warm

Snow or ice build up being rubbed against .

As to rebuilding your front differential depends on the shop that does it.

How busy they are .

How well they like you .

If more parts are needed

In days gone by I have had them rebuilt while I waited or up to a week

 

Does sound like a pinion bearing....too bad I'm way over here.....

 

It is plastic, and the front of mine broke - probably by a jack at discount tire.
At any rate, it would rub on the front driveshaft and make a noise only in 4wd.
As I said, worth a look.
Good luck !
Britt

 

Thanks for the replies, guys.


I'll check, but I don't think anything is rubbing on the driveshaft because that would make noise while accelerating also. Mine ONLY makes the noise on deceleration.


It was pretty cold when I noticed the sound (-25C /-13F), but like I said, it was WAY too loud to be considered normal. Even if it stops making this sound when it gets warm, there is clearly an issue there. I don't want to run it with a bad bearing as it might cause additional damage to differential internals.


As for the pinion bearings in the diff, does anyone have an estimate how long it would take a reputable shop to replace them? Is it significantly easier than doing side bearings?


The reason im asking is because im going to order the pinion bearings (and related items), and im wondering if I should get the side bearings also. I don't mind buying the side bearings, but if the labor to replace them is going to cost me 3 times more (compared to just doing the pinion bearings), I'd rather hold it off for now.


Thanks!

 

I'd be tempted to swap out the entire front diff for another lower Km donor as oppose to rebuilding a 350,000km clam $tyle diff, they should be easy to find even as 4.56(I have 1 here in my 97 parts truck), are you sure you got a matching front diff out of the same rig. Was the donor rig in an accident or perhaps ran dry on fluid, you don't hear of front diff failures to often. Perhaps a ripped open CV boot but they usually click like a bastard full turn under load not humm.

 

Carrier bearings are twice as easy as the pinion bearings. Normal protocol is to replace all 4 bearings. I'm guessing you don't have the e-locker so your rear is the typical V6 8" 3rd. Here's the master kit which has the 4 bearings, new pinion seal new nut, new crush sleeve.

http://www.justdifferentials.com/MKTV6-A-p/mktv6-a.htm

I have been told that finding a good shop is hit and miss.

 

As I've said earlier, im not very familiar with diffs. Is there anything wrong with rebuilding a clam shell high mileage diff? Would it end up less reliable compared to a lower mileage one, if I use OEM parts for the rebuild? (assuming a good shop does the work).
4.56 front diff will be very difficult/impossible to find in my area, let alone a low mileage one. 4.56 gears came ONLY in 3RZ 5spd 1996-2000 4runners with E-locker, which Is an extremely rare combo. I got mine from a parts truck that I purchased specifically for it's diffs. The owner had it for about 10 years and didn't know he had to change oil in it.. It did have oil in it though when I pulled it.
If there are reliability issues with rebuilding a high mileage diff, Ill considering buying a brand new OEM front diff assembly instead. I can get it for about $1000. Even if I could find a used one (highly unlikely), there is no guarantee that the same thing wont happen to it a few months/years down the road.


Another option is swapping the gears on a VERY LOW MILEAGE 4.1 diff that I happen to have. I can keep the original bearings and use the gears from the blown 4.56 diff. This way I would only need about $50 worth of parts.





The problem is with the front diff, not rear. Its a 7.5" IFS diff. Rear is 8" E-locker, but like I said earlier its from a 4-cyl truck as they were never offered with 4.56 gears in 6-cyl 4runners.

 

A small update.. I did some more research and found something worth checking out.
Someone suggested that humming on deceleration only indicates either a loose preload on the pinion bearings, or could be the outer bearing on the pinion. (Humming on acceleration only would indicate inner bearing)
I could get a new crush sleeve and a new outer bearing only and replace those myself without taking the diff apart. If this works, it would be the cheapest/easiest fix by far.

Is it possible for the pinion preload to loosen by itself? I don't think the nut can back out because its supposed to be staked.

 

It can happen I have seen that on gear sets in manual transmissions, but if that front diff has been neglected as you described it sounds like you should rebuild it if it is the rare 4.56 gearing or replace, did you pull the drain plug and count teeth to determine you have a 4.56 ratio, do you run oversized tires to require that specific ratio. Elocked 4runners with supposed 4.30 ratio are readily available and roll on 33" tires fine but you loose milage of course, but due to the availability would be a better choice, but realize you now need to swap both front and rear again which would be annoying... Research I have done tells me that it is a crap shot whether you get 4.10, 4.30, 4.56 gearing in any of the e-locker 4x4 yota's and the tag on the door isn't reliable without a tooth count.

 

Crush sleeve goes in from the front, not happening.
You can spin off the pinion nut, get a good strong hook and a good screwdriver and pound out the seal & replace the bearing and torque it, to I think 140ft pounds, I think. see if it works for you. otherwise you need to find a good 4x4 shop with a good reputation to tackle it for you.