Qyota

I've asked this question on T4R.org, but I know there are knowledgeable folks here that don't visit that site. So...

I have a '99 Limited 4x4 with OEM e-locker. 161K miles.

In drive, as I accelerate beyond about 23mph, I start to hear a low-pitch whine or whir coming from somewhere in the driveline. I have not been able to pin-point it. To me, it sounds like the rear end, but other times, it sounds like it's coming from all over the place. Details:

1. Happens on acceleration AND deceleration, and I can hear it during deceleration all the way until I stop, whereas it only starts to make noise after about 23mph on acceleration.

2. If I take the truck out of gear, the noise persists...even with the truck completely turned off, coasting down a hill.

3. Going around corners or braking has zero effect on the noise.

4. I liken the noise to a low-pitch Jetson's car...kind of a fluttery whine/whir. It's not really a grinding noise, and it's not a clunk or click.

It has been suggested that it's the rear diff. I recently changed the diff fluid, and it's in good shape with little or no bits of metal on the magnet. This wasn't always the case...the previous gear oil change showed some mush and some bits of metal on the magnet...but still not a lot. This truck is babied...never really taken off road, and driven nicely...is it likely that the rear diff bearings are shot?

What else could it be? Rear wheel bearings? Transfer case? (4wd or 2wd doesn't seem to matter).

Since it makes the noise just coasting in neutral as well, does that mean anything?

Thanks for your help.

Qyota

Also - could too much grease in the drive shaft zerks cause tension and a noise like this? That's the only other thing I can think of...and I'm planning to remove the zerk near the slip yoke to see if grease comes shooting out.

J2F42C

Does outside temperature have any effect on it?

When bearings head south, mine became much more pronounced during colder weather. With the engine not under load, I would guess it is more of a driveline issue. Ujoint, yoke perhaps? Jack up the rear, put it in N, chock the front tires and spin the rear by hand. Maybe you will hear something.

Qyota

It does seem a bit louder now that the temps have dropped.

I have spun the rear wheels with the rear end in the air, and the only noise was a little scraping from the brake drums. I know those need to be serviced because both bell cranks are frozen.

Haven't tried putting it in gear whilst jacked up yet.

J2F42C

Also have someone else drive the 4runner (scary to say) and see if you can pinpoint the sound from being able to move about freely.

It could be diff chatter since there is a locker, but since I have never torn into one, I don't want to make any broad assumptions.

If you know the drums are scraping, I'd start with a fix of the bellcranks, replace the pads if need be, and go from there. Somewhere there was a bellcrank repair PDF that originated from Tundra solutions.

Qyota

Yeah, I've been meaning to overhaul those suckers...just been putting it off. I do have the PDF of which you speak.

This noise seems to be "unusual"...which makes me think it isn't in the differential. Also, when in neutral, there is no lateral play (at all) in the driveshaft. Which I know is one way to test pinion bearing and U-joint looseness. There IS about 3/8" of rotational play though...is that too much backlash?

J2F42C

I want to say no, it is just I have not gotten dirty with my runner's driveshaft, so without that hands on knowledge, I am going to sit on the fence per se on this one.

I will be curious what the state the grease is in when you pull the zerk(s). I take it you have had the clunk and had to grease up the driveshaft.

Qyota

Removed zerk at slip yoke, and nothing came out. There is a little "old" grease where the inner and outer shafts meet, which I think it normal. Will be doing the brake job this weekend, hopefully.

James Woods

iTrader: (1)

You need to put it in gear while the rear is in the air, it is the only way you will be able to tell for sure, the noise you talk about sounds like a bearing to me, somewhere in the axle assembly being either the rear carrier bearings for the diff or the rear axle bearings, possibly front wheel bearings and maybe the sound is resonating making it sound like the rear.