Alternator Voltage Regulator Replacement - Diagnosis Help Needed

Some of you have probably been following my problems on this thread:

http://forums.tdiclub.com/showthread.php?t=131275

While trying to replace my voltage regulator today it was clear that it was bad:



However the grooves in which the brushes sit looked equally bad, if not worse. One of the wheels appears warped or bent, and there is considerable carbon build-up inside the housing.





After all the work to get the VR cover off and the VR itself out, do I actually just need a whole new alternator? I'm loathe to put the thing back together to find out it doesn't work.

Rotor Slip Rings?

Are these photos of the two copper slip rings on the rotor shaft of the alternator (the slip rings that the brushes ride on)? It that is the rotor shaft, you will need a new or rebuilt alternator because the entire rotor is shot. The next question is how did the slip rings get that way? Diesel fuel contamination?

Yes, yes, and yes. Diesel fuel contamination, and I was afraid of that...

This is a Bosch alternator in a 2001 Jetta TDI. Anybody happen to know what the part number for this is? Did they put multiple output rating alternators in this series of cars? Can I find out which version it is BEFORE I pull it out of the car?

Okay, I got the part number (028 903 028 E, 120A 14V) and Impex has one for $255.00. Looks like I can take the old one out by removing the serpentine belt and just a few screws. Will the alternator slide past the AC compressor or do I have to manuever it out the top past the coolant hoses? I don't have to take the AC compressor off, do I (typing this from work, so haven't tried anything yet...)?

http://forums.tdiclub.com/showthread.php?p=932019

Check this thread on R & R of the alternator if you haven't already...looks like the AC compressor does have to come out first.

Nice link, thanks!

I finally got all the parts together to put the new alternator in. My next question:

How much torque is required when attaching the pulley to the new alternator shaft?

Answered my own question again with a search of the Bentley: 80Nm torque on the pulley.

15 Nm on the alternator wire connection nut.

25 Nm on the bolts that hold the alternator on the car.

45 Nm on the bolts that hold the AC compressor on the car.

Can't see MITBets'a pictures any more. I seem to be having a similar problem...

Been having a fuel leak (drip) for about a year now. First, my coolant hose had to be replaced last december. This past 4th of July I had to replace the voltage regulator due to wear on the brushes.

The generator light went on again recently, so I check out the regulator and found that one of the brushes was extremely worn. So I bought a new one and replaced it. All was good for a couple of days. Then the light came on again.

Thankfully, I found the new post on replacing the seal on the fuel injection pump recently (Thanks dieselgeek!) and replaced the seal. No more leak, but the alternator is not any better.

Here's a picture of the slip rings.

Does anyone I think I need to replace the alternator? I've seen the how-to, and I'm not sure I'm up for the task. So if there is anything else I should be looking at, let me know.

Slip Ring condition

Yes, the photo indicates an alternator replacement will be necessary. It might be possible to disassemble the alternator and clean the slip rings. However, the bad threading on one of the slip rings does not look good.

Dick_Larimore said:

Yes, the photo indicates an alternator replacement will be necessary. It might be possible to disassemble the alternator and clean the slip rings. However, the bad threading on one of the slip rings does not look good.

Click to expand...

Dick, can you help us learn what you mean in the bold?

The surface of the two copper slip rings on the rotor must be very round and concentric with the centerline of the rotor shaft within 1 or 2 thousandths of on inch. This is necessary because of the very high surface speed under the brushes and the fact that the brush spring force is low. Spring force is low to maximize brush life.

Run out on the slip rings coupled with low spring force will make the brushes bounce off the slip ring surface limiting current flow in the rotor. This in turn reduces the maximum output current from the alternator. Brush life will be shortened. This becomes important because the slip rings clearly need to be "resurfaced" after all the contamination that can be seen in the photo. Diesel fuel and/or coolant contamination cause rapid brush wear. The upper slip ring in the photo has severe threading. Threading describes the rather deep "record" grooves that run around the slip ring. The brass or bronze color change indicates that the slip ring surface has got a little hot. All the brush debris and "gunk" must be cleaned from both rings. You may be able to knock down some of the high spots of the threading and remove some of the heavy filming from the slip rings using sand paper. But you have to do this evenly around the slip rings to maintain roundness.

The surface finish of a good slip ring should have a smooth and satin finish. All film should be removed revealing the original copper color. Clean, new brushes will apply a thin film to the ring surfaces shortly after the alternator is placed back into service to maintain good brush life. This light filming is not to be confused with the crud now on the rings due to the fuel or coolant.

Thanks, Dick. This probably explains why I have occasionally seen the alternator light go off while driving over the last couple of weeks, especially at high rpms or after I've taken the regulator off and blown out the gunk.

Now that the fip leak is fixed, I can focus on the alternator. Luckily, I can put the car on a charger while I'm at home and at work, so I think I can drive like this until I get a new alternator in.

This would also explain why the regulator I had in there before replacing it was worn a lot more on the upper (alt. side) brush.

Does anyone have a picture of what a new slip ring surface looks like? If not, I will take pictures and post after I get my new one.

By the way, I haven't tried, but can a person turn the rotor on the alternator by hand while it is still in the car? Or do I have to remove the serpentine belt to do that (which is what I am assuming)?

Without Heman strength, you'll need to remove the serp belt to turn the alternator by hand, which is not a hard task. Follow the instructions in this link to replace the alternator: http://forums.tdiclub.com/showthread.php?p=932019 Very good instructions, I did this recently and it took about an hour off, an hour on.

Yeah, I've seen that and figured as much. If I'm going to get underneath and start messing with it to check it, I may as well go ahead and replace it.

OK, so this thread got me tinking about the Alternator in my Dead '98 Beetle.

Since my camera is dead right now, I cant take pictures, but it looks very different than this one. There is a plastic cover on the back, then the brush assembly with the black Bosch button thingie attached to it screws off.

I took off the brushes and one brush is about .100 shorter than the other one and that slip ring is worn in about .020 where the longer brush is worn in maybe .005.

So, Dick, if I keep the car, do yo uthink I should have the slip rings replaced?

Alternator Slip Ring Wear

The alternator slip rings consist of two copper rings that are over-molded on a hollow steel core. The assembly is pressed on the end of the alternator rotor shaft. Once pressed on the rotor shaft, the shaft is spun on its center and the slip rings are lathe cut to insure concentricity to the shaft. The slip ring assembly is not a serviceable part and if the slip rings are damaged, the entire rotor must be replaced. The rotor is typically not sold as a separate part.

As long as the slip rings are round, reasonably smooth, and are not covered with contamination, they will be OK. If the wear you have on the slip rings and the brushes developed over many thousands of miles, the wear rates are quite low and the alternator still has a lot of life. New brushes placed on an old or worn-in slip ring surface initially wear at an accelerated rate until they conform to the mating surface and the wear rate will diminish. I would not be too concerned about a difference in the wear rate of the two brushes in your alternator. Remember that the current flow in the brushes is always in the same direction and the wear rate on the positive most brush is typically higher than the negative (it's an anode/cathode thing).

Thanks, Dick. I look at mine and cringe. BUt part of that is ignorance since I have never looked at these before so I don't know what to expect. I'll probably just wait and see how things shake out with this engine.

It almost looks like the slip ring is gone on a portion of mine above. I've got a new alternator coming this week. Now I just have to decide if I'm going to change it or if I have someone do it for me. I don't have a heck of a lot of time these days, but it'll probably take just as long to drop off my car and find a way to work as it would to change out the alternator.

With all parts in hand it's a 2 hour job. With basic tools and little/no expierence, I can't see why it would take more than 3-4 hours max.

Yup, took me and a helper about 3 hours all told. We hadn't gathered all the right tools and needed an extension for the 16mm wrench in order to get the new belt on (I decided to replace the belt while I had it apart, since it was showing some cracking). Turns out the slip rings were worn right through to the steel shaft. Must have been due to the constant drip of the FIP leak.

Thanks for the help and advice!