So the Touareg started chattering/chirping at idle. Of course, this happened about 700 miles outside the Carvana 4000 mile warranty so no free repairs for me.
It sounded exactly like a failing bearing. I've heard 100s of them. My first guess is the alternator. They tend to sound different than a water pump or idler. Put the redneck stethoscope on it, and sure enough, it was the alternator. Hop on the interwebs and HOLY E36 M3!!! The alternator is $800. Have these people lost their minds?
Do some more digging and Rockauto has one for $300. That's better. I ordered it and a new belt. I'll put new bearings in the OEM alternator and throw it on the shelf in case the Chinese copy dies.
Changing it wasn't too bad. A couple of intercooler pipes needed to be removed. 30 minutes and the old one was on the bench. I spin the pulley to see how the bearings feel and the pulley slips on the shaft but the bearings feel perfect. WTF? Spin the new one and it does the same thing. WTF!!
Back on the interwebs to read about overrun pulleys and bearings. Apparently, the pulley one-way bearing is a common failure. I could have replaced it for $100.
So the moral of the story, sometimes what you know to be true, isn't. And Germans build complicated stuff, not because it's better, but because it's in their nature.
Unfortunately its not a German thing. I've seen a Toyota with overrun pulleys in the alternator.
Yeah pretty common. Nissan started this in 2002
Yeah, it's apparently pretty common on the overseas stuff and some of the newer US stuff.
My question is why? What advantage does it provide?
In reply to Toyman! :
Fuel economy. Probably around .0000001%.
Slippery said:
In reply to Toyman! :
Fuel economy. Probably around .0000001%.
That's not the joke you think it is. It's basically accurate. OEM's track things that can affect fuel economy like friction to thousands of an mpg.
ShawnG
MegaDork
11/8/22 10:09 a.m.
Damn that efficiency!
Our 2019 Silverado shuts the alternator down once the battery is fully charged, then brings it online again when the charge drops.
You can watch the voltmeter cycle while you drive. Freaky until you get used to it.
I've heard that BMW was doing this electrically since maybe the mid-2000s - they would shut off the alternator at times to save power, most notably at full throttle in lower gears to improve acceleration. No power for the electrical field and it's just a free-spinning bit of metal. I wonder why other manufacturers went with a clutch instead, did BMW patent it perhaps?
ShawnG
MegaDork
11/8/22 10:39 a.m.
In reply to GameboyRMH :
I see no clutch on our Chevy, I think they just depower the field.
02Pilot
UberDork
11/8/22 10:59 a.m.
BMW also does it to optimize the battery charge, which is why you have to register a new battery (including its CCA) when you install it, so the computer can adjust the charging strategy.
TGMF
HalfDork
11/8/22 12:00 p.m.
Fuel economy. Probably around .0000001%.
In reply to Slippery :
Idiots. They could have just clamped some magnets on the fuel line and gained 10%.
GameboyRMH said:
I've heard that BMW was doing this electrically since maybe the mid-2000s - they would shut off the alternator at times to save power, most notably at full throttle in lower gears to improve acceleration. No power for the electrical field and it's just a free-spinning bit of metal. I wonder why other manufacturers went with a clutch instead, did BMW patent it perhaps?
Probably not. Honda did almost the exact same thing in the 1990s.
A one way clutch (that's not electrically engaged) isn't for fuel economy. It's to be nicer to the belt drive and alternator bearings. That way the alternator can spin down gently when the engine RPM drops quickly on a high RPM shift, rather than the heavy spinning internals of the alternator being forced to quickly slow down (I've actually seen this cause a noticeable belt chirp on shift on some engines).
Toyman! said:
Yeah, it's apparently pretty common on the overseas stuff and some of the newer US stuff.
My question is why? What advantage does it provide?
NVH. The crankshaft speed oscillates with every cylinder firing, this means the belt is also speeding up/slowing down X times per revolution. The overrunning clutch allows the heavy, fast-spinning alternator to maintain its speed.
From observation, they are able to reduce belt tension significantly. When the clutch seizes, the serpentine belt will flap and make all sorts of noise. Belts also last a lot longer now, 100k from a serpentine belt is common. And I cannot remember the last time I replaced an accessory due to a failed bearing, so accessory life has also improved. (Remember when 3800 water pumps lasted 30k miles?)
In other words, you get a whole lot of complementary benefits.
In reply to Pete. (l33t FS) :
So instead of tearing up a $75 alternator and a $12 belt every 150k, it eats a $100 pulley at 99K and an alternator is $300?
That makes perfectly German sense to me.
Yeah. If you consider the stress on the drive of spinning a high amperage alternator, forcing it to slow down on every shift is not great.
rslifkin said:
A one way clutch (that's not electrically engaged) isn't for fuel economy. It's to be nicer to the belt drive and alternator bearings. That way the alternator can spin down gently when the engine RPM drops quickly on a high RPM shift, rather than the heavy spinning internals of the alternator being forced to quickly slow down (I've actually seen this cause a noticeable belt chirp on shift on some engines).
Is this similar to what the BOM guys did with the repair on Project Binky?
Toyman! said:
In reply to Pete. (l33t FS) :
So instead of tearing up a $75 alternator and a $12 belt every 150k, it eats a $100 pulley at 99K and an alternator is $300?
That makes perfectly German sense to me.
I cannot remember the last time a serpentine belt was $12 or an alternator was $75. Hell my cost for the Volvo was like $80 for the belt and $200 for the alternator. And you are forgetting the power steering pump, the A/C hub, the water pump, the idler, the tensioner...
And as noted before, the Japanese makes did it first 
Part of it, too, is the more widespread adoption of fewer cylinders and higher output alternators. A 200a alternator will have a lot more rotating mass than a 80a one, that mass is what puts hell on the accessory drive.
eastpark said:
rslifkin said:
A one way clutch (that's not electrically engaged) isn't for fuel economy. It's to be nicer to the belt drive and alternator bearings. That way the alternator can spin down gently when the engine RPM drops quickly on a high RPM shift, rather than the heavy spinning internals of the alternator being forced to quickly slow down (I've actually seen this cause a noticeable belt chirp on shift on some engines).
Is this similar to what the BOM guys did with the repair on Project Binky?
Yes and for the exact same reason. And I still think the flexishaft will fail because it sees all the crank harmonics.
I wish my '91 Honda Civic Si would have had an rpm activated clutch on the A/C compressor. I don't know how many compressors I replaced because I forgot to turn off the A/C when I was doing a lot of high rev driving.
In reply to Purple Frog (Forum Supporter) :
Different thing.... the clutch is a one way clutch/overrunning clutch so the alternator can spin faster than the belt.
When they go bad and seize up, it is AMAZING how much the belt will flap around between the crank and alternator. It will almost sound like a rod knock at idle!
In reply to Purple Frog (Forum Supporter) :
Seriously- I thought they did.
It was a dealer installed unit. 
Not even sure you could get an Si with factory air in '91.
Purple Frog (Forum Supporter) said:
It was a dealer installed unit. Not even sure you could get an Si with factory air in '91.
You could. My mom had one I wish she kept it.
I thought they were all shipped to the US without air conditioning and got it installed at the port or at the dealership. Apparently it only took about a half hour to swap in. I'm sure having the condensor next to the radiator instead of in front of it sped things along a lot!
I'm a little surprised that there was no WOT cutout, most cars with fuel injection had that.
