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Do I need to fix a noisy differential? My mechanic says 'no.'

I have a 2004 Acura MDX with about 115K miles on it. I recently heard a slight grinding sound as the car accelerated, and I took it to the dealer for a check. The mechanic there recommended replacing the Torque Converter - a $4000 job, more or less.

Not wanting to spend that much unless it was necessary, I took it to my local mechanic. He says the torque converter is fine - that I would feel serious shaking and problems shifting if it needed replacement. And he said the grinding sound is normal for a car with so many miles on it. He says the differential gets noisy as the mileage goes up.

Who’s right? And if the problem is the differential, can I just keep driving it - as long as the noise doesn’t bother me?

Is this vehicle FWD, RWD or AWD?

A noisey differential isn’t “normal”. It would be an expensive fix so the mechanic is telling you to live with it. But, that noise isn’t good. If it is coming from the differential is means gears are wearing. Once the gears wear through the hardened surface areas they can wear and fail quickly. As the noise gets louder the time to failure gets closer.

Perhaps the gear oil in the differential has never been changed, or it got too low. There is some kind of problem. For now make sure there is good fluid in the differental. Change the gear oil every 20 or 30K miles and or every year or two. Hopefully it will last until you sell the car. Treat the differential well from now on and it might last for you is what I think you mechanic is trying to tell you.

Have you used this vehicle for towing something? Grinding isn’t a good sound. If it is a limited slip differential it is worn plates inside and isn’t good.

Thanks for the responses.

UncleTurbo - is it reasonable to think that I can drive the car for 40 or 50 thousand more miles without a failure that disables the car? To answer your question, it has never been used for towing. I may have to look more closely at my maintenance records to see if we have done anything with the gear oil.

To answer your question Caddyman, the car has Acura’s VTM-4. According to Wikipedia, that means:

“The vehicle features an automatic four wheel drive system (named VTM-4) that engages during off the line acceleration as well as when wheel slippage is detected. Additionally, the system offers a lock mode which can be activated and operated at low speeds and provides permanent 4wd and the equivalent of a locked rear differential; designed for climbing steep hills and getting out of stuck situations. To reduce drivetrain noise and increase fuel efficiency, the system runs as front wheel drive during normal cruising.”

Impossible to answer about 40 or 50K more miles because we really don’t know the source of the noise. You have a complicated drive system with 2 differentials, some kind of transfer case, and the transmission itself. A grinding noise isn’t good and it would be best to know exactly where it is coming from. Your transfer case might be locking into AWD mode inappropriately?

So far you didn’t think much of the dealer’s diagnosis. You aren’t sure what to make of the mechanic’s comments. I guess you need to find an Acura knowledgeable mechanic, take him for a drive and do whatever you do to make the car make the noise and see if you can get a firm diagnosis.

I ignored a noisy differential ONCE…Then while traveling down the highway I saw my rear drivers side tire inching farther and farther out…It was a good thing that I actually saw it and quickly got off the highway.

When complex AWD systems start making “Grinding Sounds”, repairs tend to be complicated and expensive and beyond the abilities of most mechanics…Before you lay out four or five grand on this, be SURE the shop guarantees their repair will cure the problem…

In the true American tradition, maybe now is the time to consider trading it in on another vehicle…

The comment by MikeinNH reminded me of a differential story. I was driving a Buick Century circa 1980. It was a rear wheel drive V6 midsize GM mobile. The car had about 12K miles on it and a bad rear seal. I had just picked it up as a new driver of this company car and was heading down the expressway at about 65 mph when the rear end completely locked up both wheels. There was a big bump and thump just prior to the lock up but otherwise no warning. Controlling the car was tense but I was able to guide it to the shoulder. The tire marks were pretty impressive and the car had to be towed out of there.

When a differential lets go it isn’t pretty! That’s the moral of that story. The dealer diagnosed the bad rear seal from the evidence on the inside wall of the rear tire. The fluid had been long gone, so the differential went awhile with no fluid before finally giving out.

Many people describe MDX torque converter problems as a shuddering feeling or a feeling of driving over rumble strips, often in the 40 MPH range, for what that’s worth. It sounds like you’re describing a different noise here.

If it does turn out to be the torque converter, though, you might be able to get some goodwill assistance from Acura (such as half of the cost) if you ask nicely, especially if you’ve been using the dealer for your maintenance. I’ve heard of a number of other people getting assistance of some sort due to all of the transmission and torque converter problems they’ve had. Of course, this assumes your transmission has been maintained according to the manual; if it hasn’t, don’t even bother asking.

You might be able to get more information over at

Thanks, all.

Lion9car - that is definitely NOT what I am encountering. No shuddering or anything, just a low, intermittent grinding sound, that comes from the front end (I think).

I don’t necessarily think the dealer is wrong, but I don’t want to make a costly repair if it’s not needed. We have gone reliably to the dealer for service for 7 years, and always did what was recommended. On our last visit, we were suddenly told we were due for a costly service - one we thought we had done. Then when this sound popped up, they recommended about $5000 - $6000 of work - with this at the top of the list. When we asked for a call from the manager to explain why we were suddenly getting recommendations for costly work, we never got a call back.

A few months ago, we would have trusted the dealer. Now we are more skeptical.

I think you best move might be to start shopping for a new car and trade this one in. You have an '04 high end car and when things go wrong the repair bills are very high. If you keep it, you have to start getting used to some big repair bills that haven’t been needed up to this point. Older fancy luxury cars, get very expensive to repair. Your '04 is 7 to 8 years old now and getting into “mega repair bill” time in its life cycle.

A third opinion might be helpful, so then who do you believe. 2 out of 3 wins.