Alternator Rebuild
 

At 144,000 miles on my ’88 Carrera, the original alternator bearings are occasionally making noise, as confirmed via stethoscope with engine idling. Removing the belt and spinning the fan by hand, a slight “tinkling” noise can be heard and the fan/shaft spins and coasts quite freely, indicative of dry bearings. There is no axial nor radial play in the shaft – a good sign. Belt tension is always adjusted correctly and is not too tight and proper torque is applied to the retaining nut. I’m not sure what brand of alternator my engine is equipped with, but it either has to be the Bosch or the French-made equivalent.

I feel I can finish up this year’s driving season without problems but I’d like to rebuild the alternator this winter when the car is out of service. Would like to do this job myself but searching the “How To” articles and forum postings, I’m unable to find anything – seems most folks just take their alternator to a specialty shop. It would seem that a general refurbishment would consist of replacing both bearings, new brushes, polishing the slip rings and a thorough internal cleaning. Obtaining new sealed ball bearings would not be a problem but I’ve not seen brushes offered by our host, or any other supplier for that matter. So, for any of those that have rebuilt their own alternators, my questions are as follows:

1) Where can brushes be obtained for these alternators?
2) Are there any unforeseen “surprises” that might be encountered, requiring
special tools, etc.?

Thanks guys – appreciate any advice and suggestions.

Yea, the search "engine" here is hopeless. So check out this thread.

http://forums.pelicanparts.com/porsche-911-technical-forum/941604-alternator-bearings-again.html

This is not for the faint of heart. I would not attempt this yourself unless you have some experience with motors/generators. BTW, the parts are available.

You may want to find a shop that specializes in alternator rebuilds.

Fixed it for yah :D

Dave,
never done it, and not sure how much parts will cost you, but usually local rebuild shops will charge between $100-$120. In case you want to know.

This is not hard, and can be very rewarding. European manufacturers use several standard sizes for bearings and brushes. Searching the net will provide you with sources. Napa stores are also a good source. Measure the cross section of your old brushes to find replacements. If I remember correctly your brushes are soldered to the voltage regulator, and an easy replacement. Rob

I had a local auto electric shop do a complete rebuild of my alternator three years ago and it was $175. I was hesitant to take it to that shop even though I had used them several time for Detroit irons.

However, I walked through the door carrying the alternator, and even before I got to the counter, the guy says, "Oh, an air cooled 911." That certainly calmed all my anxiety.

Thank you gentlemen - all the info I requested was supplied...much appreciated!

Our local shop does it for $75-125 depending on the parts needed.

My local auto electrics shop does a rebuild for about $100. The thing about going to a good local re builder shop is they will replace the diodes, bearings, and anything else needed, then return it
looking like new.
A rebuild from a FLAPS is a crapshoot as most industrial rebuilders
have to deal with crappy cores and their products are very hit and miss.
At least with a local shop rebuild you know you are starting with a known good core, yours!
I used to rebuild my own, but now I let the pros do it.

Agreed. I will, sometime soon, take my alternator and two starters to the local rebuild shop. They do a complete job at a fair price. The guys I will take them to are old (they know what they are doing). When they are gone, I suspect this may no longer be an option.

By and large, brushes are replaced when the VR craps out. Or you just get a new VR, with its new brushed attached (they all come that way).

If you have a lathe, you might be able to turn the commutator (that brass segmented thing the brushes contact if I have my terminology right). I don't know that using sand paper is going to clean a worn one up suitably.

Which is why going to a specialty shop is the path of least resistance for most of us, even frugal DIY guys like me (though I don't have a lathe anyway). They are all set up for everything, can test output to start with, and then after they are done.

I've rebuilt several alternators myself, including the one for my 911.

IMO, it's really easy to do, not sure I'd ever pay a shop to do it unless I couldn't source the parts myself. (Some of the parts, like the rectifier, can be difficult to purchase retail -- at least for these alternators)

On mine, I replaced the worn brushes and bearings, then polished up the commutator with a bit of sandpaper. My car is similar mileage to yours and the commutator still looked to have plenty of life in it.

Of course, this isn't a ground-up rebuild, but I find that those are rarely necessary, unless you're dealing with voltage issues from the alt. And if that's the case, it's usually an issue of a bad rectifier (low voltage, excess AC voltage in the system) or voltage regulator (high voltage or sporadic charging).

To replace the brushes, you can either solder new ones into the VR (easy, basic soldering), or get a whole new VR unit with fresh brushes (VR replacement is super-easy). I got the brushes for like $7 on ebay. (dimensions are 4.5mm T x 6.5mm W x 14mm L x 46mm). Replacing just the brushes saves money and means you keep using a known working VR.

I used a shop press to drive out the front bearing on my alternator, but I bet it's possible using a socket and hammer. I was able to get new bearings from McMaster by just entering the codes on the old bearings, cost me less than $20 for both.

If you do it yourself, be careful with the little plastic cup that holds the rear bearing in.

If your alternator is putting out correct voltage, I wouldn't worry about replacing the rectifier. And at that mileage I'd be surprised if the commutator is worn beyond use.

Honestly, I think the hardest part is just getting the alternator out of the car itself. John Walker had a great tip about separating the alt from the fan housing. (http://forums.pelicanparts.com/porsche-911-technical-forum/454747-can-not-seperate-alternator-fan-housing.html)

So, yeah, taking it to a rebuild shop is probably the easiest, but I'd say that rebuilding it yourself is pretty low-difficulty if you're fairly handy.

Replacing bearings is easy, and you can buy much better quality than a local rebuilder will use...

But where can you buy a commutator? Someone posted a source but can find it. Would be easy to press a new one on...

I have bought some carbon brushing from internet and sand them down to the correct dimension. Just making sure you buy those carbon brushing that have spring similar to your original one and longer or fatter so you can sand them down to correct dimension.

Pretty sure Wagner Alternators has this part, and I found it on a couple other sites. The problem was that they do not sell to retail customers -- ran against this obstacle with a few places that stock alternator parts.

The alt in my '86 is a Valeo design, apparently, so you can find parts by looking under that alternator type. Pretty much everything you'd need is available -- commutator, stator coil, rectifiers. Just not retail.

Kind of a bummer, since the parts themselves weren't particularly expensive. I suppose you could try to buy the part from an alternator shop.

Alternator is the only thing that ever left me stranded... right before a 7 mile long tunnel (!) was leaving Geneva. Far from home I had the common traveller problems : choices, time and tools
were nonexistent so I had a local guy do it. It's the ONLY time my car has been to a mechanic in 45,000 miles of ownership .. I think the bill was VERY expensive. I could've bought a watch!

Surprises?
1) Brushes stick in holder and don’t slide freely,
2) Hold down spring cracked and doesn’t provide necessary pressure
3) Solder on diodes is old. Not something easily visible but allows diodes to easily pull out. Resolder the diodes.

I experienced the first two during the same rebuild.

What a wealth of great information! Thank you all for your contributions. I'd like to do the job myself just for the satisfaction of doing it. But the specialty shop is attractive also, especially if they could handle it for around $130.00.

Respectfully, I have watched a guy rebuild alternators and starters and he had the text equipment and expertise. He tested the various circuits within the windings, for example. You mentioned parts availability which is important, as you say. If a winding were leaking, he might have a source for that. Maybe no, but he might.

This is my choice. But then again, I am 62 and should retire but I haven't, and that means there are demands on my time. Plus cooking and gardening and music and guys and relatives and friends and..... If I cannot not get my alternator rebuilt (and my starter, likely this winter) I might just get a new one. But I'd likely be less confident of the new one than a locally rebuilt one. The guys in Tacoma know what they are doing. They will retire soon.

Alternator Rebuild
 

I'm glad I took the advice of those on this forum to have my alternator rebuilt by a professional shop. At 144,000 miles on my '88 Carrera, the alternator bearings were making that dry "rustling" sound and so this Spring, when the garage was warm enough to work in, I removed it. Took it to a local auto electrical rebuilder and got it back in 7 days.

http://forums.pelicanparts.com/uploa...1586883178.jpg
http://forums.pelicanparts.com/uploa...1586883268.jpg

This is the 90 Amp Paris-Rhone alternator which is common on my vintage Porsche. I instructed the shop to go through it thoroughly, clean, replace bearings with non-Chinese - made parts, and replace anything suspicious. They found quite a bit of parts that were worn out.

http://forums.pelicanparts.com/uploa...1586883344.jpg

The slip-rings were severely worn (actually worn through in one spot) and these were replaced:

http://forums.pelicanparts.com/uploa...1586883431.jpg

The brushes are non-replaceable as separate parts and the whole brush holder and regulator is replaced as an assembly. Brushes were right at the end of their travel:

http://forums.pelicanparts.com/uploa...1586883501.jpg

New bearings are Japanese-made NTN brand, which are very high quality.

I feel that this alternator was severely worn out and caught in the nick of time. Thus, my recommendation is for others with 3.2 L engines with 100,000 miles, you might want to have your alternator serviced.

Getting caught up on maintenance items now that the coronavirus has me housebound. Since most Spring PCA events are cancelled, it's a good time for a detailed and extended maintenance program.