mlkovacs

I have a 1999 4Runner SR5, V6, 4WD, stock, automatic, regular differential, +240k miles, I've owned it since
new, full synthetic, mostly highway miles, but recently we're building a house, so I've been
pulling a trailer here and there. If I'm not driving the 4Runner to work, the family goes to build
the house (2 adults, 2 kids, 2 dogs), so there's weight inside.

We've noticed a noise/whine. It starts when the vehicle starts to move, and eventually gets drowned out
at higher highway speeds (+75mph). The pitch of the whine goes up with the speed. The whine occurs
regardless if we accelerate, decelerate, or coast in neutral. The whine is there regardless of road
surface (smooth or chip seal), and the smoother the road surface, the more you can hear it because
there is less competing noise. The noise is the same if the vehicle leans left or right.

I lifted the front, and the wheels are tight, no play and they spin nice with no noise or friction.
I then thought it was my worn aging tires, but after replacing all 4 tires, the whine is still
there.

I replaced the rear diff fluid (prior was Amsoil full synthetic), but same whine. I went about 40k
in-between diff fluid changes. The fluid was darkish, and there were some metal shavings on the
plug.

I took the 4Runner to Toyota, and they found the whine/noise coming from the rear, not the front.
Toyota wanted ~$640 just to tear down the rear differential to determine what the issue is. I don't
have that kind of money right now (i.e. I'm building a house), but will cough up the money if I
know what the problem is. I'm not comfortable spending $640 and only then knowing when I'm getting
into.

Any ideas? I'm thinking pinion bearing?

Malcolm99

It could be any of the bearings in the diff, so it would be wise to replace them all and get a quote for that accordingly. You could easily remove the 3rd member and take it in and save the $640, and then pay to have all the bearings done. Or you could also by a complete 3rd member and just swap them out, it isn't to bad of a job if you have a helper. Once you have the diff out the ratio is stamped on the ring gear if you don't trust the door or unsure of your the spin test, you don't want to order the wrong ratio.

*It could also be the axle bearings they are carrying all the weight and more likely to wear out and cheaper to replace so you might start there instead.

skypilot

iTrader: (1)

Sorry; its time. Pull the pumpkin and rebuild. Should just need new bearings pressed on and the big nut torqued. My personal experience is 75w-80 on these. Thick doesn't lube the roller bearings properly and they fail. I think its the same reason Dodge Challenger differentials fail so often. Lube looks good on paper, but real world its too thick to get in and do the job. And yes I do use 10w-30 motor oil in my diffs for years without issue, it may not work out for you.

coryc85

240k is getting to where I would want to change those rear axle bearings for peace of mind, not saying that is your issue here. You can drop the diff end of the rear drive shaft and check for any play in the companion flange, maybe your pinion nut can be tightened a bit. I guess wearing of bearings plus maybe fatigue on the crush sleeve can cause some slop there, and a loose pinion would probably whine. That's a quick check that might let you drive it for a bit longer if you can eliminate the whine, while you save up the cash to really get in there and replace bearings. I replaced the axle bearings on my 88 4Runner myself (purchased a tool from ebay) because the dealer price was ridiculous and the independent shops were not much better. If I were going to pull the axle shafts, well I'd just go ahead and pull the diff out as well at that time and do it all at once.

mlkovacs

Oh ya, I'm definitely getting it fixed. This 4Runner has been amazing for 19 years. This is our only vehicle, so either I drop it off at Toyota and pay the big bucks, or rent a car for a day, and pull the diff off and take it in. I'm definitely not a mechanic, but I think I'm half decent...I've already replaced the timing belt twice, and replaced the front left CV.

akwheeler

For the price of "taking it in" if you pull the axles and differential out yourself you may as well price out a complete 3rd member ready to bolt in. Get a quote from the shop for just bearing replacement and for a complete rebuild with ring and pinion if you drop off the diff. Compare that to what a new 3rd member would cost you.
I would also recommend that you replace the wheel bearings and axle seals while you have them out, but if you don't know what you are doing either study up a lot on this forum or take it to a shop that knows Toyota.
for now, like coryc mentioned, check for play in the pinion and if you find some tighten the pinion nut just until the play is gone and order up the parts.

wyoming9

iTrader: (1)

This is one of those things it might stay together for another 100,000 miles or explode the next trip.

I had one made so much noise I waited for it to explode every day .

After 50,000 miles I sold it like it was.Not like you could miss the screaming !!

I guess Gear oil is one of those things for years I used 85/140 in everything no problems I was aware of .

Because I am cheap and a 55 gallon drum seems to last for years

Malcolm99

I agree using the correct oil will make these things last longer, I use 75W90 Synthetic in all my 4R's and in a 2012 Tacoma front centre and rear diff, thicker is not better in these little diffs.

dropzone

iTrader: (6)

you are not gonna get it back from the dealer in a day..3 days best case and my guess is that they would sent it out to have some one set up the third. Gear set up is sort of an art form in my opnion.

Getting a new third is a good idea.
Find a flat spot to park
chock the front wheels
place rear axle on jack stands
remove tires/wheels
remove brake lines
undo driveshaft
undo the 4 14mm bolts on the backing plate
pull each axle--Do not let them rest on the axle seals--that being said now would be a good time to have new axle bearings pressed on to your axles
remove the rear third

reinstall new diff and repeat the process,
I unfortunately have done this so many times in the 30+ years I have had toyota trucks I can pull a third in about an hour