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740 "Whirring" sound

colgate41

Active member
Joined
Jul 31, 2008
Location
New York
1991 740 Turbo, auto with 190K. Car is not my daily and has been sitting with occasional starts and drives around the block.

I've noticed this audible "whirring" sound coming from under the car around the transmission tunnel when driving.

It seems to start around 10-15 mph and gets louder as speed increases. If I shift the car into neutral as I'm driving, the sound is still there. The automatic transmission seems to **** fine and as it should. Overdrive button/relay work fine.

The best I can describe the sound as is a whirring that increases in volume as I go faster and decreases as I slow. When the car is idling at a stand still the sound is gone.

Can't remember the last time I changed the tranny fluid and like I said, this car is not a daily anymore. This whirring problem happens when the car is hot or cold. Spring or winter. Light research seems to bring me to a clogged or dirty transmission filter? Any ideas? Thanks!

I recorded a video of the sound;

https://drive.google.com/file/d/1-hPI83Jr3t6bdwHw-0aSmK0-KqhUrMmh/view?usp=sharing
 
If sound increases linearly with vehicle speed, cause is from OUTPUT of the trans back to the driven rear end. Most likely driveshaft center bearing, but could also be trans rear bearing (long shot). U joints another possibility but less likely still.

Sound correlates with vehicle speed; IF you have access, put the front on ramps & the rear axle on jackstands..... and have someone engage the gears whilst you listen/video what's happening around the driveshaft(s).
 
If sound increases linearly with vehicle speed, cause is from OUTPUT of the trans back to the driven rear end. Most likely driveshaft center bearing, but could also be trans rear bearing (long shot). U joints another possibility but less likely still.

Sound correlates with vehicle speed; IF you have access, put the front on ramps & the rear axle on jackstands..... and have someone engage the gears whilst you listen/video what's happening around the driveshaft(s).

Thanks. I'll check it out!
 
I had a loud high pitched noise that I passed off as a wheel bearing...until my center u joint froze cause the center bearing to basically seize... I put the car on stands and tried to locate the noise. I could not still. I had to remove driveshaft and physically move the u joints around. The center bearing was crusty and no good also
 
My 91 240 would make that same noise, sometimes with a scratching sound I figured it was the trans, but it always worked fine so I didn't worry about it
 
Just wanted to update this thread.

As I've worked on other parts of the car, I've been driving it more and more to shake it out and stretch it's legs. I haven't gotten under and inspected the driveshaft and carrier bearing area yet but I do suspect (hope) that's my issue. I was able to take a short video and capture the sound the car is making. If anyone has had this problem and found an answer, just let me know and let me know if it's something else.

Yes, I know I'm missing a bolt for my passenger seat!

Here is the link;

https://www.youtube.com/watch?v=bs0M_IwXR5Y
 
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