rear diff droning sound?

[98_Q_silver]

I am new to this site. I just bought a 98Q and we love it. It's got 144,000 miles on it and it looks and drives like new. It has been very well cared for and was driven by and older couple.

I get this low droning sound going down the road. I kind of think it's the tires but I hear it from 10 mph on up. Around 40 mph the sound is really noticeable. The pitch doesn't seem to change under acceleration or coasting. I maintained speed and shifted the trans out of overdrive and even down to second. The sound frequency stayed the same. Maybe a u-joint? Worn out diff? I changed the diff oil last week and the noise is the same. I did notice that the magnet on the drain plug was covered with something kind of gray in color, I suspect that the oil had never been changed. I don't know. I know it has not been abused or driven hard. Could it be a rear wheel bearing?

[Infinitiguy19]

When you say "grey stuff" do you mean metal particles?

Was all of the oil black or just the a little bit of it that came out?

[98_Q_silver]

The oil was pretty dark. Not black like really old motor oil but dark. It didn't have any burnt smell to it. I drained out the old then pumped a quart of 80/90 valvoline in and then spun the tires around by hand for a bit then drained it out and filled it up with new valvoline 80/90. The grey stuff was stuck to the magnet but came off easy with a rag. I am not sure if they were metal particles or not. Maybe clutch material?

[qship96]

If diff. fluid has not been changed at 25,000-30,000 mile intervals FROM DAY ONE, 144,000 miles is a long life and noise is to be expected, and will slowly get worse as the miles pile on......changing fluid now will not un-do the damage done.Might want to try going to a thicker gear oil to mask the noise from the slop in the gears due to the wear....try 80w-140 FULL synthetic gear oil{ Redline,Amsoil,Mobil1}
Modified by qship96 at 7:27 PM 9/12/2008

[98_Q_silver]

thanks. I will give it a try. I guess I better plan on a new diff soon huh?

[maxnix]

Or a low mileage take out, which is always a gamble.

[SteveTheTech]

The black stuff is pretty common actually I have seen that in most Infiniti rears when people change them at 60K, as most people do. Since it's magnetic it sounds like gear wear, the black stuff is usually a little clutch material.

I would also check the rear wheel bearings, spin the rear wheels while they are off the ground and hold the spring and listen. While turning the wheel you should not feel any vibrations in the spring and/or hear a faint noise from the wheel area if the bearing are good. If the bearing is not good you will feel a rolling almost clicking in the spring and hear a rolling metal on metal noise.

A wheel bearing is much cheaper than a rear pumpkin. It's worth checking out.

[98_Q_silver]

You did mean spin the tire by hand right? I am half wondering if it's the tires. It sounds almost like tire noise. Almost as if I had Goodyear gatorbacks on it.I even get a little vibration through the steering wheel at slow speed.

I will try the wheel bearing check and also replace the gear oil with a heavier grade. If it is the diff, then the sound should change with different oil.

Thans for the input. I will keep you posted.

[SteveTheTech]

I should have phrased that better. Yes you are right spin the wheels by hand.

What type of tires and what conditions are they in?

Tire pics?

[SteveTheTech]

A heavier weight oil will work for short term (my father used to use this on his Ford) to suppress the noise slightly. It's no guarantee but it may be worth a shot if the bearing check out. But since you have a vibration issue it may be tires/alignment.

[98_Q_silver]

The tires are crappy Bridgestone Insignia SE200. I would guess about 10,000 - 15,000 miles. Never rotated but in fair condition. The fronts had some slight cupping going on so I rotated them. Now that I think of it, the noise is somewhat worse than before I rotated them.

Check this link from the Tire Rack for a review of this tire.

http://www.tirerack.com/tires/...SE200

[SteveTheTech]

I can understand why you would get those tires but they do not have the best reviews. These tires have a soft tread compound and small contact patch so they are very susceptible to wear especially when they are not rotated.Knowing this I would change my previous statement to tires being the issue. Almost enough to bet the farm on.

[maxnix]

The black stuff is pretty common actually I have seen that in most Infiniti rears when people change them at 60K, as most people do. Since it's magnetic it sounds like gear wear, the black stuff is usually a little clutch material.

Why 30K is the correct interval, or sooner. Never any color in my lubricant other than original.

Do any Infiniti differentials have clutches?
Modified by maxnix at 11:14 PM 9/17/2008

[98_Q_silver]

I just bought this car a couple weeks ago. The tires were already on it. My pick would have been the BFG Traction T/A T 235/55R16. They are an inch wider but the same diameter and way better ratings. Cheep too. I have been buying from the Tire Rack since 1985 since I grew up in South Bend IN where they started up in an old gas station.

http://www.tirerack.com/tires/...2FA+T

[98_Q_silver]

Not sure what is in the Infinity diff as this is my 1st Infinity. I would guess that there is some sort of clutch mechanism since it's a viscous limited slip diff.. The color of the stuff on the magnet plug was not black. It was a grey color and it wiped right off. The oil was a little darker than the new oil but not too bad.

[SteveTheTech]

Why 30K is the correct intermal, or sooner. Never any color in my lubricant other than original.

Do any Infiniti differentials have clutches?

They use a viscous coupler. I was not sure so I did some quick reading.

I just bought this car a couple weeks ago. The tires were already on it. My pick would have been the BFG Traction T/A T 235/55R16. They are an inch wider but the same diameter and way better ratings. Cheep too. I have been buying from the Tire Rack since 1985 since I grew up in South Bend IN where they started up in an old gas station.

http://www.tirerack.com/tires/...2FA+T

Those are ok, Personally I like these as they can be cross rotated to ensure proper wear. I don't like the way those BFGs wear and ride. It's just my 0.02 http://www.tirerack.com/tires/...ace=7

[SteveTheTech]

It has probably been replaced then.

There are other things that are usually recommended and many people over look differentials. I don't know why. I always recommend things based on visible driving wear,smell, color and mileage.

[98_Q_silver]

I was just looking for that online. I wonder what's in the coupling?

[SteveTheTech]

Ill be honest with you I don't know, I am now on a mission to find out. I have not been with the company long enough to ever rebuild one. It's just not really done anymore it's just not cost effective for anyone in these days.

[98_Q_silver]

Avid T4's were my 1st choice but they suck in the snow and we get our fair share here in Indiana.

I will try to get those two tests done tomorrow and post it up for ya.

[maxnix]

My pick would have been the BFG Traction T/A T 235/55R16. They are an inch wider but the same diameter and way better ratings. Cheep too.

That last sentence should be a big red flag, unless you are getting advice from Tweety Pie.

The coupling is filled with silicone fluid. You guys need to read some of the old posts. Thoroughly discussed how they work and fail. I don't think the coupling is available sepatately, but maybe Steve can tell us.

When I asked the dealer here if they cahnged the differential fluid at 30K, he said "No, we look at it to see if it is good or not." To which I said, "Isn't it a little too late then?" Other than maybe engine oil, you want to regualrly replace all fluids before degradation is evident for maximum performance.
Modified by maxnix at 9:16 AM 9/13/2008

[SteveTheTech]

Ill be honest I suck at searching the forum for anything relevant to this topic. The ESM doesn't list the operation characteristics of the viscous coupling. I could take a shot in the dark but I have never had one apart.It's a shame though and I would really like to get my hands on an old one to take apart and study. I have studied the removal and installation process for the ASE tests and my personal knowledge, but being one of the "young" guys I am from the new school in which it is much more cost efficient to replace the whole unit rather than rebuilding the unit. Most shop do not even have the correct tools to do this job correctly.

The more I read this forum the more I like it there is a wealth of knowledge out there and I have learned a bunch from owners experience.

There are a few reasons that differential services are overlooked by many people and not on some shop maintenance schedules.

If I can get my hands on one of these older diffs I will be sure to take it apart and post pics of it.

[maxnix]

I'd still be interested to know if the unit is available by itself.

[SteveTheTech]

The viscous coupler or the whole pumpkin?

Off the top of my head I think a QX4 rear is a grand with preload and pinion depth already set. I'll call my parts manager and see if he knows.

[maxnix]

No, just the coupler. Seems like that would not be too difficult to replace.

[SteveTheTech]

Disassembly of the unit seems pretty straight forward. Having to measure preload and turning torque is time consuming and requires many costly specialty tools. I am sure you can find people to do it out there, if you were to go to the dealer the labor charges would be more expensive than a new unit. With a new unit you don't have to worry as much about backlash and preload.

Setting up a rear end is a dying art form. I have seen it done a few times but only on personal cars never a customers.

[98_Q_silver]

Just an update to let you know that there is no update due to Ike dropping quite a bit of rain here the past couple days. I am not a fan ov working under cars in the rain.

Could I have a driveshaft u-joint going out. I noticed that there aren't any grease zerks on them. How a bout CV joint going bad. It does have 144,000 miles. The boots look good though.

Side note: What model NGK spark plugs should I use?

[maxnix]

Side note: What model NGK spark plugs should I use?

RTFSM!

zeroforum?id=24

[98_Q_silver]

I know I am new here so what does RTFSM! mean??

Read The Factory Service Manual??

[maxnix]

Yes! Easy to tell, but better to learn!