Rear diff noise 99 LTD

[dradeka]

Hoping someone might be able to give me some guidance here. I've searched the threads but haven't found this specific complaint. We have a 99 Limited automatic with the locker. It has 170K miles and has been in our family since new so we have all the service records and driving history. It is probably a 60/40 mix of highway/local with very limited towing and very limited light off road use. When we put the truck in gear (D or R) and with the brake still applied (sitting still) I can hear a kind of vibrating/clunking noise.

When I crawl around outside the truck listening (with my son at the wheel taking care of shifting from N),the clunky noise is clearly coming from the rear diff. There is no such noise once driving (or at least we can't hear anything). About 20K miles ago my mechanic told me that there was "increased hum" from the rear diff and that it may be "on the way out." At that point (right or wrong) I decided to just keep doing rear diff fluid changes once a year and keep driving it; the mechanic agreed.

So now I'm wondering what to do next. I'll probably swing by the shop tomorrow to have my guy listen to it.

Am I in for a diff replacement? Should we keep driving it until it goes? My son currently uses the truck mostly locally to get back and forth to work here in town so it is only getting maybe 100 miles a week of use right now.

Thanks in advance for any insights.

 

[99problems]

Not sure, I just wanted to point out that you've been a member since 2003 and have only posted 13 times. That's an average of 1 post every 16 months. Not a negative, just interesting. Sorry I can't provide actual help, but it does sound to me like you've got a dif swap or rebuild in your future.
:cheers:

 

[dradeka]

I really don't know what to make of your comment. I moderate a technical forum that has to do with the restoration and maintenance of a particular class of sailboat, where because of my experience I am very active and constantly answering questions for years.

Some of those people might also come in once every 18 months or so with a question, which I answer without questioning their motives, because it is the right thing to do.

I'm not that knowledgeable about cars; I'm just looking for some help from those that are more knowledgeable than me.

 

[99problems]

Does it make a consistent grinding noise when you're rolling? My first thought is that your pinion bearings are shot. You may have to get the rear end up on jack stands to test this since it isn't the loudest noise and might not be something you can hear from the drivers seat. Here is a video from a Tacoma diff rebuild that shows what that sounds like (at ~ the 1:05 mark in the video): https://www.youtube.com/watch?v=sltHP4jQY8I

Edit: actually the more I think about it the pinion bearing would get louder with speed most likely, so you'd probably notice it at speed. Perhaps your backlash is out-of-whack on your 3rd member? I would normally question if there was enough grease in it, but since you mentioned that you've been doing regular fluid changes that's unlikely to be the cause.

 

[Devbot]

^^^ I was about to recommend pinion bearing, they're usually the first to go and will typically clunk a little. Would also explain the hum. You can google how to check it manually, but the long and skinny is removing the prop rod and trying to wiggle where it connects to on the 3rd member (the pinion face I believe it's called), feeling and listening for play as you do - there doesn't have to be much to cause noise so be paying attention (though if it's clunking I bet it's somewhat significant.)
Off the top of my head I know East Coast Gear Supply sells replacement 3rd members for only $700 or so, fwiw

 

[Cree]

^^^ I was about to recommend pinion bearing, they're usually the first to go and will typically clunk a little. Would also explain the hum. You can google how to check it manually, but the long and skinny is removing the prop rod and trying to wiggle where it connects to on the 3rd member (the pinion face I believe it's called), feeling and listening for play as you do - there doesn't have to be much to cause noise so be paying attention (though if it's clunking I bet it's somewhat significant.)
Off the top of my head I know East Coast Gear Supply sells replacement 3rd members for only $700 or so, fwiw

I couldn't diagnose with the wiggle method, but while the rear shaft is out it's pretty easy to toss it in 4WD and go for a spin. If he doesn't hear the noise, it's likely pinon related. Still there? It's further into the diff. My pinon was SILENT with no rear shaft. Deafening at speed with the shaft installed. YMMV.

 

[dradeka]

Ok my son is taking my runner to work today; so I'll have a little time during lunch to take this one for a spin and see what else I can hear. Thanks for the tip regarding the supplier; I wasn't even sure where to start. Google is not your friend here as you get a zillion hits when you type out "99 4runner rear differential."

Thank you for the advice; I'll let you all know...

 

[3bears]

agree it could be the pinion bearing. I had one go out with little noise, just vibration that I thought at first was drive shaft related.

but just a wild guess....thought....question.....

since its a locker.....how often do you engage the locker....could the locker mechanism be making noise.....like sticking....or holding something half in and half out
I siad that was a wild idea.....but I would try the locker a few times....why not try it ? My last one that had a locker I would click it on and off at least one time a month in summer, in winter I tested it often. ( I get lots of snow and ice, got 4 inches yesterday)

how about wheel bearings and/or excess spressure, is the breather functioning correctly ?

another out there idea.....what kind of fluid are you running. My son had an older taco that had a slight rear end howl, but no vibration. He changed fluid ( to look for metal shavings) and replaced with synthetic and after a short time .....few days....the howl went away, could have been just coincidence. However he did sell about 2 months later to get a newer one so dont know if that was a "real" fix.

best of luck

 

[phattyduck]

If you can be without the truck for a bit (couple weeks, maybe?) and can DIY the diff removal/install, Zuk does a great job with diff rebuilds:

Toyota Gear Install Harrop

He did the 6.7" in my Alltrac, but mostly does truck diffs.

-Charlie

 

[jlaho]

I can't recall if the drain plugs on our diffs come with a magnet or not. If they do, great. If they don't, I would suggest removing the rear diff fill and drain plugs and adding a small neodymium magnet in the recess on the plugs

Install the plugs, drive as you normally would for 500kms or so. Pull the plugs and look for any ferrous debris. Any bearing or gear failure will produce wear metals that will collect on the magnets. A thin layer of fine metal on the magnet is normal for any decent length of service. Large amounts of metal paste or large flakes will confirm you have an internal failure and will need a replacement soon. This is a method is commonly used in industry.

Sounds like your mechanic already diagnosed a potential failing diff due to a hum. If you are hearing new (worse) noises, I would suspect they might be on the right track. If you do the test I mentioned above and confirm your mechanic's diagnosis, then replacing the diff would be best for the truck. A failing diff could leave you stranded and damage your upper powertrain.

Best of luck!

 

[dradeka]

Ok so this has been a bit of a mystery for several days and has turned out to be really stupid and simple.

To answer a few of the questions, yes the locker has been engaged occasionally in some deep snow situations and also a couple of times when my son was offroading. It worked well and there was no "sticking" or noise.

In terms of fluid we have had the diff fluid changed out with a synthetic (I don't remember the spec).

So the klunking noise did not reappear for a day or two, and then reappeared sporadically, but we isolated the pattern to when the truck was warm.

A bunch of crawling around underneath revealed that the damn exhaust hanger is loose and when it is warm the exhaust sags just enough when the trans is in drive, for it to touch and vibrate on the frame member above the diff.

What a stupid PITA this was!


So we're going to tighten that up, continue driving it and just keep an eye on the diff hum, which is still not great.

I appreciate the questions and tips; I will keep this stuff in mind.

 

[3bears]

good to hear it ight be as simple as that. Noise can travel and sound like it is coming from someplace else or a vibration can sound like a hum.