Rear wheels spinning in neutral?

dschultz · 11-14-2016, 01:50 PM

I had my baby up on jackstands with the wheels off. With the engine idling in neutral the rear hubs were spinning slowly. Easy to stop just by holding the hub by hand, but I've never noticed this before. Of course, I rarely run the engine while the car is in the air. Is this normal? An indication of clutch wear? Should I be worried?

pungo · 11-14-2016, 05:06 PM

Since all the gears in the trans are spinning, yes the the wheels can turn from oil drag on the output shaft of the trans. I've seen it with other cars, though I never tried it on my Z4.

The HACK · 11-14-2016, 05:12 PM

Normal. All manuals will do this.

If my understanding of manual transmissions is correct, while in neutral the driveshaft is disconnected to the input shaft, but the entire clutch/pressure plate assembly is spinning freely while immersed in transmission fluid. That motion influences the output shaft and cause it to spin despite the two shafts not physically being connected.

While on the ground that motion is easily overcome by the friction of the tires vs. surface. When up in the air, enough energy gets transferred over to cause free hanging wheels to spin.

EDIT: What Pungo said.

dschultz · 11-15-2016, 10:44 AM

Got it. Thanks for setting my mind at ease!

thrak410 · 11-16-2016, 12:28 PM

Quote:

Originally Posted by The HACK

but the entire clutch/pressure plate assembly is spinning freely while immersed in transmission fluid.

I agree that its 'fluid friction' but I dont believe this car (or any car that I know of) runs a wet clutch setup.

pal · 11-20-2016, 11:14 AM

Quote:

Originally Posted by thrak410

Quote:

Originally Posted by The HACK

but the entire clutch/pressure plate assembly is spinning freely while immersed in transmission fluid.

I agree that its 'fluid friction' but I dont believe this car (or any car that I know of) runs a wet clutch setup.

Agreed on theory, but our clutches are dry and sit outside the "transmission" so to speak. And, I have observed the same on my car when on stands.

thrak410 · 11-20-2016, 02:41 PM

Thats what i said... ?

pal · 11-21-2016, 12:16 AM

Quote:

Originally Posted by thrak410

Thats what i said... ?

Yes

I guess there was some redundancy in my post.

11-14-2016, 01:50 PM	#1
dschultz Private First Class 26 Rep 195 Posts Drives: 07 Z4MC Join Date: Sep 2012 Location: Bay Area iTrader: (2)	Rear wheels spinning in neutral? I had my baby up on jackstands with the wheels off. With the engine idling in neutral the rear hubs were spinning slowly. Easy to stop just by holding the hub by hand, but I've never noticed this before. Of course, I rarely run the engine while the car is in the air. Is this normal? An indication of clutch wear? Should I be worried?
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11-14-2016, 05:06 PM	#2
pungo Colonel 877 Rep 2,544 Posts Drives: Z4MC-X3-35i-525i, Corrado G60 Join Date: Nov 2007 Location: MD iTrader: (5) Garage List 2011 BMW X3 x35i [0.00] 2001 BMW 525i [0.00] 2007 BMW Z4 M Coupe [8.76]	Since all the gears in the trans are spinning, yes the the wheels can turn from oil drag on the output shaft of the trans. I've seen it with other cars, though I never tried it on my Z4.
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11-14-2016, 05:12 PM	#3
The HACK Midlife Crises Racing Silent but Deadly Class 1821 Rep 5,337 Posts Drives: 2006 MZ4C, 2021 Tesla Model 3 Join Date: Oct 2007 Location: Welcome to Jamaica have a nice day iTrader: (1)	Normal. All manuals will do this. If my understanding of manual transmissions is correct, while in neutral the driveshaft is disconnected to the input shaft, but the entire clutch/pressure plate assembly is spinning freely while immersed in transmission fluid. That motion influences the output shaft and cause it to spin despite the two shafts not physically being connected. While on the ground that motion is easily overcome by the friction of the tires vs. surface. When up in the air, enough energy gets transferred over to cause free hanging wheels to spin. EDIT: What Pungo said. __________________ Sitting on a beat-up office chair in front of a 5 year old computer in a basement floor, sipping on stale coffee watching a bunch of meaningless numbers scrolling aimlessly on a dimly lit 19” monitor.
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11-15-2016, 10:44 AM	#4
dschultz Private First Class 26 Rep 195 Posts Drives: 07 Z4MC Join Date: Sep 2012 Location: Bay Area iTrader: (2)	Got it. Thanks for setting my mind at ease!
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11-20-2016, 02:41 PM	#7
thrak410 Private First Class 86 Rep 166 Posts Drives: 2004 Z4 Roadster Join Date: Jun 2016 Location: Canton, GA iTrader: (0)	Thats what i said... ?
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