Cracked Flex Plate?

[ElNormo]

I've got a funny rattle coming from, what sounds like, under the middle passenger seat area. About where the hump covers the drive shaft. It's noticeable after driving for a little while, when letting go of the gas pedal or when braking. When applying the gas pedal, the sound goes away. It sounds like someone put playing cards in the spoke of a bicycle. The rattle slows as the car decelerates. Obviously tied to the speed of the engine and/or wheels.

While I normally take the car to an independent BMW mechanic, I decided to save a little time and drop by the corner shop. They listened to the car on the road, then reproduced the sound with the car in the air. They believe the sound is coming from the transmission. When standing under the car, you can hear the sound, faintly, coming from the small grill in the bottom of the transmission. While they're not familiar with the specifics of the transmission, they said it sounded like a cracked flex plate.

This is well beyond my transmission knowledge. Does a cracked flex plate make sense? I'm assuming any fix would involve dropping out the transmission, which would be costly.

Thoughts?

Thanks!!

Norman

[ArnZ!]

Does it sound like this? http://www.youtube.com/watch?v=_D1Z9tbKdxA

[SnakeyesTx]

Sounds more like your guibo came apart and the nylon threads are slapping against the transmission tunnel.

If you had a cracked flexplate, you'd have a sound incredibly similar to a thrown rod, and it would only make that noise for a few days before it broke free from the flange and freewheel the engine.... ask me how I know ;)

[Ross]

Could it be described it as a ratcheting sound?
I doubt it's a flexplate. Maybe a torque converter.

[ElNormo]

Thank you all for the responses. I agree that it doesn't seem to be coming from the transmission. The sound is coming from rear of where the transmission would be. It really sounds like it's coming from the hump over the driveshaft in the rear seat footwell. I'm going to take my wife out for a drive and have her sit there and listen.

Also, I'm working on getting a recording. I thought I had one, but it didn't come out. I'll put that online tomorrow.

It definitely sounds like something plastic-y slapping against the outside of, well, whatever it's in :-)

Thanks, I'll post an audio clip tomorrow. Or maybe even tonight.

Norman

[ElNormo]

Okay, thanks to my understanding wife, we have an audio recording:

http://wnelto.people.wm.edu/rattle.wav

This is the sound of me coming to a stop, fairly abruptly. In order for this to start happening, we have to drive on the interstate for 10-15 minutes to get the car "warmed up", so I think temperature obviously has something to do with it.

After a while, the sound happens any time I let up on the gas pedal, and gets noticeably louder when applying the brakes.

We're both convinced the sound is coming from right under the driveshaft "hump" in the rear seat.

Thoughts?

Thanks!!

Norman

[SnakeyesTx]

I still think it's the guibo, but then again that sounds quite a bit more "frictional" than mine did. Get her up on a lift and look for the "clean" spot where it rubbed.

[genphreak]

Be sure to post back with the exact problem ElNormo, this'll help people in future if you can verify the precise cause.

[adrian.j]

The flex plate or guibo.... Mine went and at first it made a card in the spokes sound but after not knowing what it was and being lazy about seeing what it was, it eventually fell apart all the way and the bolts on the output shaft and the drive shaft got bent. So fix it before you need to replace these parts. New output flange= 350$ new drive shaft=75 new flex plate=50$ new knowledge= priceless

[Mordan]

Does it sound like this? http://www.youtube.com/watch?v=_D1Z9tbKdxA

what was that?

[rockin1978TA]

My wifes 89 535 made the same exact noise. It is the driveshaft center support bearing. What happened to mine is the front u joint hooked to the transmission locked up, causing no flex in the driveshaft. This wears out the rubber bearing support in the middle of the driveshaft. What your hearing is the bearing or the bracket holding it banging on the heat sheild between the floor board and drive shaft. I ordered a new bearing from BMA and installed it, but since at the time I didn't realise the ujoint was locked, it ony lasted about a month. This is a job you only want to do once, so if you replace the bearing, also ha ve the u joints looked at. If you go with another drive shaft, make sure it is the same year, as I found out a 89 and 92 use different diameter front shafts, which needs a matching heatsheild.

[genphreak]

... New output flange= 350$ new drive shaft=75 new flex plate=50$ new knowledge= pricelessLOL!

Yea, if it has to come out due to a noise, the other parts in the chain need to be carefully inspected. Bank on a new quibo, uni and centre bearing- plus new grease where the rear of the tailshaft links to the diff (final drive).