Replaced My Alternator And Had A Pleasant Surprise

[old guy]

I replaced my alternator today as a preventive maintenance. I figured that at 230K+ miles it was time. I really don't like being stranded on the road. The alternator on the CC VR6 went out at an inopportune time with just over 235K miles on it and it ended up costing a little over $1K to get it back on the road (Long story, but the best option at the time).

I know..... I could have ordered a new regulator pack for around $50 and replaced it. But that could mean also replacing the slip rings and maybe a bearing or two. Plus additional down time. I'm not into down time.

For $130 I picked up a rebuilt 150 amp Bosch alternator. The core charge was $70 so I figured I would dissect the OEM alternator and see if I wanted to refurbish it as a spare or just return it for the core charge.

It took a leisurely 1.5 hours start to finish. Pretty easy job. As soon as I started the engine I noticed a difference. The idle sounded smoother and felt smoother! What the hell??? So I went back and closely examined the OEM alternator and sure enough, the overrun pulley was completely locked up. I had no idea that it could make that much of a difference. 4 bangers inherently have strong pulsations at idle. Apparently by engaging/disengaging the alternator between pulses it makes a very noticeable difference.

I'm happy

[A4orce84]

Nicely done sir! I had to grab a refurb Valeo unit from Autozone last year, as mine went out during a semi-inopportune time.

Way to be pro-active on the maintenance side! =)


Thanks,
Asif

[DarkoNova]

Overrun pulley?

Never heard of that on an alternator. I'm guessing it's to limit output at higher rpms?

[old guy]

It's simply a one way clutch. So if the engine speed slows down the alternator can continue to spin freely. It reduces the on/off alternator load on the drive belt. Here's some good info on how they work: Clicky click®

[5ktq]

Yeah, I never tested mine yet but I am convinced it is has sized, due to the amount of tensioner flop. Fixed shaft makes the tensioner pick up the slack. (Something about.. angular velocity not being even)

On mkiv golf, TDI had them and gas doesn't, I guess the effect is exaggerated with diesel's lower idle and stronger strokes. It's also relevant during shifting, and having the clutch run will make life easier for the belt and tensioner.

I guess the AWP (1.8T in GTI) might have been able to get away with the fixed pulley due to having a .. 90A/120A alt, but our 150A is bigger and more rotating mass, I'd guess

[DarkoNova]

Interesting. How do you test it?

[Chemmie]

My 1.8's serpentine belt tensioner oscillates at idle as though the belt is rapidly gaining and releasing tension. After reading this I'm thinking it's the alt pulley clutch rather than the tensioner itself.

[EuroxS4]

One way clutch pulley on the alternator is expensive as shit.You can probably buy 1 or 2 alternators for the price of the pulley.Most go to a pulley that doesnt have the clutch in it.Clutch is there to put less drag on the motor when its not needed.

[5ktq]

they're only $40 for INA, plan on ordering one myself

[Kevin C]

Good tip!

[Matt Devo]

the alternator is one of my few original parts left, and like yours has 235K+ miles on it; will have to keep an eye out for one

[old guy]

the alternator is one of my few original parts left, and like yours has 235K+ miles on it; will have to keep an eye out for one

I did partially dismantle my OEM alternator and it was in better shape than I had expected. The slip rings were in great shape. The brushes were worn down maybe 60→70% so they probably could have made it to 300K. The bearings felt smooth when spinning by hand. The overrun pulley was the only thing that needed immediate replacement.

Oh well…One less thing to worry about.

[BumblebVR6]

When the pulleys go bad, they'll start to "chirp" as the belt jumps on them when they lock up. Mine went bad at around 100k miles. Ordered the pulley thru my VW parts dept. (when I was working there), the spline tool to remove the pulley from the Cornwell truck and swapped it out. Has been good to go ever since. Picked up a spare INA pulley as well that I keep in the toolbox for next time (if) it happens.