Hi,

I have a 2010 S40 T5 AWD R Design with 120k miles. I've been searching online and have seen a lot of forum threads with people discussing their rear differentials and the humming noises they're making. All seem to say the same thing, that if it needs to be replaced it's expensive. I don't know the first thing about cars so all the technical talk doesn't do me any good.

Back in early spring I noticed a noise of what I thought was a prop plane flying over my car. I looked online and research indicated wheel bearings so I took it to the dealer. They replaced both front wheel bearings which took care of the noise that I was hearing and cost me about $1,200. They continued to inform me that the rear differential in the car is going as they see metal pieces in the fluid. They said that this would cost $6k brand new and about $3,500 used. I don't really have any interest in spending that kind of money with the mileage I have on the car. Ideally I'd like to keep it until it dies and purchase a new Grand Cherokee as a second vehicle.

Long story short, my question is has anyone had experience with this issue and not fixing it? I'm wondering how long I can get out of the car before it isn't drivable any longer. The dealer says the differential will just get louder and louder until I can't bear the sound any longer. Having no knowledge of cars my fear is that I'm driving down the highway at 75 MPH and the back end of the car just falls off.

Any thoughts are appreciated.

 

I've never heard of a differential (or transmission for that matter) just falling off :-)

I've had both fail on different cars over the years - in one case (a BMW 2002 (1973 model) the rear end failed by "opening up" ie a main gear was spinning on its shaft. No noise, just boom, no power to the wheels. If you have a locking differential between front/rear, you should be able to limp home... I had a tranmission bearing fail on another car and it just started to scream, but I was able to make it home (about 75 miles), so I agree with your mechanic's assessment that it will just get noisier giving you fair warning. What you may want to try inspecting the bushings to make sure you're not getting extra noises due to a broken mount, and consider drain/fill the differential with top shelf synthetic gear oil. I'd also check for leaky seals etc. That may get you a bit more usage while you monitor the noise level. I'd be curious about your driving habits that would put stress on the differential - ie lots of ice and snow etc?

If you want to price a used replacement, check out Car-Part.com--Used Auto Parts Market

 

Typical driving habits in New Jersey. Most of the 120k miles are highway in typical New Jersey traffic. So it isn't any extreme snow ice. When the dealer first brought it up he said there wasn't anything that he could point to that would be the direct cause of the issue. Said that he had replaced 3 rear differentials recently.

Ideally for me I'd get another couple of years out of the car without any major issues. If I can get up near 200k miles I'd be very pleased and then if I do go out and purchase a Grand Cherokee i'll be splitting miles between the two which will help prolong both vehicles.