Drivetrain Grinding Noise

[johrt]

Hope you guys can help out here.

95 318i, Automatic, 186Kmiles. New tires, new brakes.

Driving back from IL. last Sunday (500mi round trip). No problems, car humming at 80mph, gas mileage at 30mpg. Pulled off interstate and noticed when slowing down the car started making a grinding noise.
- Sounds as if coming from Passengers side.
- Almost sounds like a worn set of brake pads.
- Car made the noise from about 40mph until stopped.
- Will start making the noise again up to about 30mph and then disappears.
- Makes the same noise regardless of if the brakes are applied or not.
- Makes the same noise when coasting in neutral.
- Makes the same noise if the e-brake is on or off.

Does not do it around town, speeds kept under 30 - 40mph.

Put the car up in the air and could not locate the noise with the car in gear at speeds of up to 60mph.

Pulled the rear tires. Found nothing amiss with the rear brakes or rear wheel bearings.

Inspected the rear diff. A bit greasy. Checked fluid levels. A bit low, so changed and refilled. Same problem.

Unable to inspect the drive shaft carrier bearing. Buried under the exhaust and heat shields. Inspected the front drive shaft flex coupling. Appears to be brand new. No wear, nice and glossy (new rubber look) black.

Also rotated front tire. Bearing appears to be ok. Plenty of pad life left.

I am at a loss. Almost ready to pull the "Carrier Bearing" trigger and replace it. But just pulling the exhaust could be a major undertaking. Hate to do so if the problem lies elsewhere.

[Pirate_copy]

Sounds more like a wheel bearing mate...

[johrt]

An update.

Had 2 passengers in the car last night. Problem started as we were leaving the driveway. My youngest son asked if the sound we were hearing was the problem. I asked for his opinion from where it was coming from. I said right side. He said left side. My rear seat passenger said middle of the car, between the front seats.

Based on this I think I will pull the trigger on the support bearing.

I will let everyone know how this turns out. Keep the suggestions coming!!!

I will also take another look at the wheel bearings as well.

[motorwerks]

If you get it in the air you can just spin the wheels, and you should easily be able to tell if it's a wheel bearing or not. The support bearing is a common wear item, so I wouldn't be surprised. The should be changed every 100k based on their normal rate of failure according the BMW techs I use to work with.

[carlos244]

What is the most economical and effective way to check wheel bearing for the humming noise?

[motorwerks]

What is the most economical and effective way to check wheel bearing for the humming noise?

Bad wheel bearings often cause excessive play in the wheel. If you put the car up on jack stands you can grab the wheel from the 6, and 12 o'clock positions and try to shake it back, and forth. You should also take the opportunity to spin the wheel, and listen for any grinding or knocking.

Sadly the above method doesn't always work, because the wheel bearing isn't always bad enough to cause the wheel to rock, and the grinding will sometimes cease when there is no load on the wheels. This takes us to the next method.

Often times with a passenger you can detect wheel bearing noise by just driving, and listening. I recommend with a passenger because they can usually better detect where the noise is coming from. Drive at the speeds that you usually detect the grinding/knocking sound, and see if you and your passenger can determine where the noise is coming from. If you can find an empty parking lot, use it to rapidly steer left, and right. You should get a significant increase in noise when the vehicle load shifts to the wheel with the bad bearing.

[funbmws]

What is the most economical and effective way to check wheel bearing for the humming noise?

I wondering how many miles you have on your car. I have a 330i 2001 with about 85K
and seems like I have the same humming particularly when going to stop.

thanks

[johrt]

Just finished up with the car. Here is what I found.

Performed a 2nd visual inspection. Found that part of the floor insulation had come loose and was rubbing against the front drive shaft flex coupling. Does not explain the noise, but does explain the rubber smell when parking the car.

Pulled the cat back portion of the exhaust. Be prepared to replace a lot of broken rusted bolts. Then removed the aluminum heat shield. Some gentle prying of the exhaust gave enough room to remove it.

Next up was the rear heat shield / drive shaft loop.

With all of this out of the way it was time to pull the drive shaft. 1st marked the drive shaft, and flanges to insure that all went back into the same orientation. Pulled the bolts, and then the shaft. The center support bearing spun freely, but was a bit noisy. A quick R&R of the bearing and reassembly.

The test drive was perfect. The noise was completely gone, including some of the existing background noise. The car is really quiet now.....

I would like to thank everyone for all of their help and suggestions!!! Overall, it was a 5 hour on your back type of job. Sure wish I had a 2 or 4 post lift!!!!

[johrt]

BTW 186K miles on the car and still going strong!

[BMR_LVR]

Congrats on your repair. :thumbup:

Feels great to fix something yourself doesn't it.

Thanks for letting us know what the problem was. May have to use your post in the future to refer to.

[tmoritz]

You wrote:

"- Sounds as if coming from Passengers side.
- Almost sounds like a worn set of brake pads.
- Car made the noise from about 40mph until stopped.
- Will start making the noise again up to about 30mph and then disappears.
- Makes the same noise regardless of if the brakes are applied or not.
- Makes the same noise when coasting in neutral."

I had the exact same symptom, though it got loader and loader over a couple of days. Had the center bearing replaced (it was done). Overall cost at Auto Edge: Just under $500. :cry: Noise has gone and I'm happy despite the cost. ;)

[N:CR41G]

Could it be a tailshaft bearing? I had this same problem on my e30!?

[BMR_LVR]

If the OP had taken a test drive after removing the insulation that had fallen down, he likely would have found that the noise was gone. I had the same issue and all it took to get rid of the noise was to remove the offending insulation. If interested, see the link to my post:

http://www.bimmerfest.com/forums/showthread.php?t=341143&highlight=

I would have never thought in a million years that just a peice of insulation could have caused the noise, but it did.