Alternator pulleys and other Alt. rant

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So, this never used to be a thing. My wife's current and previous car both had alternator pulley failures in less than 4 years 45K. Both of these were Bosch alternators with the sprag clutch in the pulley failing.

Her current BMW just had the replacement alternator replaced because a bearing went out in the alternator and it screeched and seized - taking out the belt. It's not a big deal as the original alternator was replaced under the new car warranty and her dealership warrants any replaced parts for life. Last time the pulley went out they replaced the alternator, the belt and the idler pulley. Now at 85K all those items are covered due to the lifetime warranty from the original alternator replacement. But two mechanical alternator failures in one '08 car with less than 90K on it? Evenly spaced at around 40K per alternator? She still has the OE brake pads with a good bit of meat left!

If you include her audi which also went 40K on an alternator, she has had 3 new alternators each live ~40K miles on cars that were new in the last 10 years.

I like the idea of the clutched pulley, but it would appear a failure point has been added. Her previous car was an '04 Audi, her current car is an '08 BMW (which has really been low maintenance compared to the horror stories and the Audi).

Previously my wife has had alternators fail in other new vehicles. The ones that come to mind were her Oldsmobile and 2 Nissans ago.

I have never had an alternator fail in one of my vehicles. I live in Florida, so the A/C is always on. My road is dangerous, so I always have the headlights on and I typically have an oversize stereo in whatever vehicle I drive. As my daughter says, she knows the radio is up too loud when it makes the car wiggle.

I typically put 200K on a car without any alternator issues, my wife has rarely made it to 80K without an alternator failure. She drives very sedately. Her commute to work is a perfect 70-80MPH, 20 miles each way with a few miles of 45mph at the end. I drive in a lower gear usually, zing to redline whenever possible and my ride to work is 25 miles of highway with multiple stop lights and 2 actual stops (where I have to turn off and restart the car) each way.

Is it just luck? Is it because she spends all her time at low RPM and I am always 3K+ (more airflow?) Is it car design? Is it Bosch? To my logic, I should be wearing out alternators and she should never have any issue. In both of my cars the alternators are low and behind the radiator. In her current and previous cars the alternators are up pretty high and behind the radiator. Maybe mine get cooler air?

To be fair, I have spent more money on brakes in the last 10 years of my car than what it would cost me to replace her alternator with OE parts twice, but I just don't understand why, in this day and age, alternators fail. I can understand when highly stressed, complex engines and transmissions, abused suspension components and even power window mechanisms fail. But alternators should last hundreds of K miles - as should water pumps.

I'm just amazed that this is a thing. Anyway, I just wanted to rant and don't know where else to do it.
 
alternators have much higher output these days, but didn't grow as much physically. I'm not surprised they get pushed harder as cooling is concerned. short trips seem to be the killer, the alternator has a lot of work to do after starting and gets warm. if you stop the car before the alternator charge and temperature has reduced, that heat will get to the parts that are lubricated or to the electronics.

We had a customer with a "powered everything" diesel engined SUV who ran very short commutes (no more than 2 minutes). we changed or repaired his alternator at least 5 times in 50k miles.

He traded that car in and got another SUV from us. we haven't seen him back with electrical issues. We sold his SUV on and haven't seen that back either bar for maintenance.

one was a hyundai santa fe, the other a mitsubishi outlander.
 
My understanding is that the sprag/damper pulleys are mainly to extend *belt* life, because the belt doesn't have to absorb the swap in tension when the engine decelerates and the alternator's rotor tries to keep spinning (most alternators turn at between 2x and 3x crankshaft speed, too, so its a pretty good slug of kinetic energy.)

So they've engineered it so the serpentine belt system can now last 100k miles... and also so the alternator pulley no longer lasts indefinitely
frown.gif
Also the belt/tensioner people (Gates, Dayco, and so on) have bought in big-time because they now sell an integrated kit with the tensioner, belt, and a new alternator damper pulley and make noises about denying warranty on the belt if you don't replace all 3 at once. Alternator replacements and repairs had gotten to be a very rare thing for me after the 70s- our 93 Chrysler went 250k on one alternator, my daughter's XJ is still going on its original at about 165k (knock wood). But those both had solid pulleys. Not quite sure what to expect from the SRT and WK2 with the new fancy-pants damped sprag pulleys. I have seen that at least one cottage industry got started supplying parts to replace the damper pulleys on later CVPIs with solid pulleys for police departments because they were having unacceptable failure rates.
 
Makes me think of the 1960's and 1970's cars, every few years many would need a rebuilt alternator installed (in addition to a rebuilt starter).
 
Research BMW efficient dynamic charging system & you'll see how the way the way alternator disengages on acceleration. This constant on/off beats the pulley clutch to death. The Denso system on Toyota/Lexus works much better
 
Originally Posted By: cat843
New wife


New? It's just like car parts; you can get on the internet and order one from Taiwan that's perfectly fine for a few years
grin.gif
 
The engineeering credo ought to be "add "simplicity" but it's not. Lots of alternators used to be changed when the problem was just worn brushes.
 
Last edited:
Originally Posted By: 440Magnum
My understanding is that the sprag/damper pulleys are mainly to extend *belt* life, because the belt doesn't have to absorb the swap in tension when the engine decelerates and the alternator's rotor tries to keep spinning (most alternators turn at between 2x and 3x crankshaft speed, too, so its a pretty good slug of kinetic energy.)


This ^^^

Just imagine while driving how long a clutch would last if four or five times a minute you depressed clutch, revved engine to/near red line then dumped it...

For most part I've had little to no alt issues, but I've never owned a vehicle with said clutch pulley... My Marauder had one but had been removed when supercharger was installed..
 
When I first saw them, I thought they were a good idea.

When I saw a 100% failure rate in my applications I reconsidered.

My Wife, though, she's a keeper.
 
Originally Posted By: TFB1
Originally Posted By: 440Magnum
My understanding is that the sprag/damper pulleys are mainly to extend *belt* life, because the belt doesn't have to absorb the swap in tension when the engine decelerates and the alternator's rotor tries to keep spinning (most alternators turn at between 2x and 3x crankshaft speed, too, so its a pretty good slug of kinetic energy.)


This ^^^

Just imagine while driving how long a clutch would last if four or five times a minute you depressed clutch, revved engine to/near red line then dumped it...


Well, its not necessarily that bad. Whenever the alternator clutch disengages, it means that the engine is slowing down rapidly (say, shifting gears). The alternator rotor itself will spin down a little more gradually, and as its rpm gets close to the pulley RPM (determined by the engine) the sprag clutch just re-engages smoothly when the RPMs match, and there's a spring mechanism to damp out the initial engagement. There's never a situation where the clutch is dis-engaged and bangs into engagement and has to rapidly accelerate the alternator rotor. Well, unless its a stick and you miss a shift, maybe... ;-)
 
there's another couple aspects to this--- the belt tension is controlled by a spring-loaded idler in many cars -- and if you have something like the alternator with a lot of stored momentum yank the belt if the engine suddenly decelerates like at a downshift, the alt can yank the belt, pull the tensioner, and the backup of extra belt elsewhere pops off.... and now no belt.

they also keep the tensioner pulley tension lighter to extend belt and accessory bearing life.

I bought the little tooklit from amazon to swap the overrun clutch on the chrysler alternator. Made it pretty easy to do. Depending on the orientation, could be done in the car, and it's far cheaper than a new alt.

While it's a lttle more complex, the 3.8 engine plant is one I really like. it's quiet, the belts do actually last, and aside from those clutches I have yet to see an accessory fail on any of the later model chrsyler products in the family. (other things break, small electronics, knobs and switchgear.... they have their problems just not where we're speaking).

-m
 
Originally Posted By: Miller88
Torque converter clutches operate in a similar fashion. They lock and unlock all the time. AC Compressor clutches too.


Clutch life largely depends on the surface area, the loads and the frequency of engage/disengage action.

If you notice an alternator pulley does not provide much in terms of the surface area for the clutch material to take up the load. Also, alternators produce quite a parasitic load when providing full current. So if the ECU programming allows for cycling the alternator pulley clutch when high current loads are needed, it stands to reason that such an action would have a detrimental effect on clutch life.

Also, TC lock clutches, AC clutches and gearbox clutches are considered wear items and they do wear out, so having a clutch on the alternator simply adds another wear item.
 
Originally Posted By: Ethan1
Originally Posted By: cat843
New wife


New? It's just like car parts; you can get on the internet and order one from Taiwan that's perfectly fine for a few years
grin.gif



Isn't it cheaper just to get them rebuilt??
smile.gif
 
Originally Posted By: KrisZ
So if the ECU programming allows for cycling the alternator pulley clutch when high current loads are needed, it stands to reason that such an action would have a detrimental effect on clutch life.


I think there's some confusion here. Most (I won't go so far as to say 'all') of these alternator clutches are PASSIVE devices. They don't engage/disengage under any sort of control, they just let the alternator spin down at its own rate when the engine speed drops suddenly. That way you don't get a big tension reversal in the belt system with the inertia of the alternator rotor trying to keep the belt moving, rather than the belt driving the alternator.
 
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