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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old February 17th, 2008, 12:40   #1
Veteran Member
Join Date: Jul 2006
Location: Parkton, Maryland
Default Alternator, Replace voltage regulator or rebuild/buy rebuilt alternator?

I have a 1997 Passat TDI with 230,000 on the odometer and the original alternator. It was draining a new battery (2 months old) until the battery light came on intermittently, then over an hour period of time to full on. I checked across the battery terminals with the engine on and only got 12 DC volts with the engine at idle (903 RPM). With the engine off, I got 13.2 volts across the terminals. I immediately suspected the alternator, since I have been fastidious checking and cleaning all grounds, including the hard to reach ones. After realizing I could not get the back of the voltage regulator off on the engine due to the tension spring adjuster for the serpentine belt adjuster wheel, I bit the bullet and pulled the alternator off. Brushes are 3 and 4 millimeter (mm) long with minimum spec at 5 mm. I sanded the ends of the brushes a bit, pulled them out some more carefully, then cleaned all the dust/dirt up and went over all connections to be sure they are clean and bright, including where the alternator connects to the mounting bracket and inside where the bolts go through the supports to be sure the alternator is well grounded as I wanted to eliminate the ground as a problem. There was corrosion from age on all connections and enough to maybe reduce voltage charge to the battery, but did not know for sure. Got it all back together (man getting that bottom bolt to line up so it goes into the threads is a mighty unpleasant task!!!), charged the battery up all evening and night and the voltage is now 14.2 volts across the battery terminals with the engine at idle (903 RPM). Battery light is now off and over a 20 mile drive has stayed off.

Question to those down this road before me is this: Do I just replace the voltage regulator or do I just rebuild this alternator or get a rebuilt Bosch alternator? Does the voltage regulator contain the rectifiers as well as the brushes or just the brushes? The windings, etc. all seem in good shape as the Bosch 120 amp alternator seems to be well built. When I spin the pulley, it is tight with no real noise to it. Money is very tight right now, but I don't want to be penny wise and pound foolish, but the extra $130 is golden right now.
This board has been the best, so what say everyone?
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Old February 17th, 2008, 13:05   #2
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Join Date: Sep 1997
Location: Illinois
Fuel Economy: 50 MPG

Simply replace the voltage regulator.


Brian, 2015 Passat SE TDI 6MT
Kathy, 2014 Passat SE 2.5
Chris, 2015 Passat SEL TDI

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Old February 19th, 2008, 16:37   #3
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Location: Parkton, Maryland
Default Votage Regulator It Is!

I ordered a new voltage regulator from World Impex yesterday and it is in late this afternoon. I will let everyone know how it goes. My battery light has been off as well as my CEL light after a couple start/stop cycles. My CEL has been off and on for about 8 months and nearly always on before the massive amount of work I did to get it up to snuff! This board is the best, thanks BK!
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