"Thunk" sound from rear wheels

[maxwax]

I've had an intermittent problem with my 2014 CX-5 (AWD, Touring) for several months.

The symptom is an audible "thunk" sound accompanied by a slight vibration both of which appear to come from the rear tire or tires.

I first noticed this when I'd leave work. My car would be parked in such a way that I could normally pull forward and to the right before straightening out to leave the parking lot.

While turning, the right rear tire would slip a bit as though for a second there was something underneath it like an acorn or something. Imagine the wheel suddenly being able to spin for an inch or two then getting traction again. That sound and slip then grip is what my symptom sounds like.

Unfortunately, I can't reproduce this easily. I talked to the dealer but they hadn't heard anything like this before. I've been waiting for the problem to get worse so I can bring it in and more easily get it fixed under warranty.

This problem almost always happens when I'm turning. On the highway or city roads at 5-90MPH there are zero problems with the operation of the car. I'm always starting from 0 or < 5 MPH and accelerating forward while turning. After the first thunk, I normally don't hear it again on that trip. Let the car sit for a while, then head out again and I might hear it.

Any ideas?

AFAIK, this is a problem with my individual CX-5 and I don't expect many others to have it also. I'm just fishing for someone who might have had this or something like it so I can investigate further.

Thanks,

 

[Bopper]

I would remove that rear wheel, inspect the lug bolts for anything unussual and reinstall that rear wheel, just to confirm it is really on there corrrectly. It sounds as though you are feeling some sort of shift occurring.

 

[Bladecutter]

Does it only happen while going forward, or while backing up?
Do you always set your parking brake?

It could be one of two things:

Brake pad that was slightly stuck, has freed up, or the ABS self test.

You should have a friend or family member drive your car in the spot that it always makes the noise, exactly how you drive it when it happens, while you stand outside, and listen for the noise.
If you are able to reproduce the noise every time you make the same maneuver from your parking spot (lets say you did it 4 times back to back), then it would be something I would pull the wheels and look at.
If it only does it the first time, but then the next three times is silent, then it most likely one of the things I mentioned.

BC.

 

[GAXIBM]

If you are setting the parking brake it may help to grease the rear caliper slide pins so they don't stick with the pads engaged. The sound may be the pads breaking loose...

 

[pjensen641]

....

This problem almost always happens when I'm turning. On the highway or city roads at 5-90MPH there are zero problems with the operation of the car. ...

Damn! Don't even know how long it would take my '13 little 2 liter to get to 90

I agree with the lug nuts thing. In addition, jack up the rear wheels, grab the top and bottom of the wheel and try to rock it up and down. You are checking for loose suspension components etc. There should be no play at all. One more thing to think about is that many times during the winter, you will actually have water free up between the disk and brake pads. When you start moving, you will get a loud clunk when the ice breaks.

 

[TreyP]

I would agree with the parking brake guess, if you are indeed setting it while at work. It could be a rusting cable and/or mechanism that is releasing all at once to produce the intitial clunk which wouldn't be heard again until the brake was set again.

 

[xtrailman]

I can hear the brake pads sometimes clunk as I set off, i've had this with other cars, especially if the car is parked with wet disks.

Try parking without applying the handbrake, use wheel chocks if necessary, I always leave the brake of if I park it in the garage wet, or after just washing the car.

 

[CX5Dude]

My rear brake pads were seizing in the holders. the dealer had to cut the pads away and repaired under warranty as I was still under 20,000kms. Mazda has not yet admitted this is a problem but areas that use liquid de-icer on the freeways increase the problem.

 

[TreyP]

I was thinking about this on the way in this morning and I came up with 2 more possible causes.

1) As we all know, sometimes ice, snow and salt will combine to cause a huge buildup in the wheel wells. Although I generally knock this off for safety reasons, I have noticed that some days when I come out of work, this mass of frozen sludge that I haven't cleared yet will have loosened and fallen onto either the ground or gotten loosely wedged between the tire and the wheel well. So, perhaps you are driving over this frozen mass which is causing the clunk/shudder as the ice breaks beneath the weight of the car.

2) Depending on temperature patterns, sometimes the tires get frozen to the ground and you are feeling the car break free from this condition.

 

[maxwax]

Hi, everybody. Thanks for the all the comments. I never considered the brakes and the dealer only inspected the area around the differential with no talk of the breaks. So when I go in for an oil change this week I'll discuss that with them.

This isn't a winter thing as it definitely has happened during the summer and fall.

The one time I've really heard this rather loudly is when I park it in the garage. I back in slowly, then stop, put it in park and set the brake. When I leave, I lower the brake, put it in drive and slowly go forward. When doing this I've heard some fairly loud thunks. A brake that won't release until force is applied certainly sounds like something I should look into. It also definitely seems like its the rear passenger side more than anything else.

I'm going to try to reproduce this tomorrow, but I don't think I'll be able to. IF it is the brakes, you can understand why just going through this procedure might not do anything. But park it, let it sit, then move forward.. That would give the breaks some time to stick and expose the problem.

I really don't want to give up my car for a few days to investigate this, but I want to make sure this is resolved while it's still in its first year of warranty.

Thanks, again!

 

[maxwax]

Just before my CX-5 reached its 1 year anniversary, I took it in to the dealer to investigate this issue.

They ended up replacing the entire rear differential -- under warranty! -- and this has completely fixed my issue.

While investigating they changed the diff fluid and found it to be dark colored with metal shavings.

I didn't do this earlier because the symptoms described were very intermittent for the first few months, then they got worse. Recently, I moved into the mountains west of Boulder, CO and my daily commute home included a couple miles of windy incline switchback. I'd hear the thunk noise on nearly every turn and definitely every day.

Now, no noise at all, just like everyone else

Sil-Ter Har motors in Westminster Colorado did a great job investigating, contacting Mazda for approval and once the parts arrived, I had a fixed car within 24 hours. Really happy with them right now.

 

[Chris_Top_Her]

Just before my CX-5 reached its 1 year anniversary, I took it in to the dealer to investigate this issue.

They ended up replacing the entire rear differential -- under warranty! -- and this has completely fixed my issue.

While investigating they changed the diff fluid and found it to be dark colored with metal shavings.

I didn't do this earlier because the symptoms described were very intermittent for the first few months, then they got worse. Recently, I moved into the mountains west of Boulder, CO and my daily commute home included a couple miles of windy incline switchback. I'd hear the thunk noise on nearly every turn and definitely every day.

Now, no noise at all, just like everyone else

Sil-Ter Har motors in Westminster Colorado did a great job investigating, contacting Mazda for approval and once the parts arrived, I had a fixed car within 24 hours. Really happy with them right now.

I had my fluid changed at 35k front and rear. They didn't say anything so I'm guessing it didn't look bad.

 

[MikeM.]

Thanks for the update. It's always good to know you have a dealer that will take care of you.