Need Recommendations on Alternator Replacement
 

It's almost Spring and time to tackle a reasonably big job.

I'm convinced that my alternator (unknown brand) has some fatal problems as I've been down the alternator-light-won't-go-out road for about a year. Changing the external regulator didn't help. Tightening the belt to 1/4" slack didn't either. The alternator puts out about 15.6v at 3000 rpm under load.

Our sponsor sells quite a variety of brands, rebuilt and new. My engine is a 2.7L '75S or Carrera, same specs.

If you were in my shoes which brand/condition alternator and external regulator would you purchase, bearing in mind that both must be from same manufacture? Any other surprises that I should be aware of?

Thanks in advance,

Tom

Absolutely, positively rebuild the old alternator, and in parallel take advice from this Board on what you might replace it with. Why? Just read the tales of folks trying to get rid of their Paris Rhone or ? unit and find themselves having to further tweak other areas to make the new unit work.

Bottom Line: Unless it never worked well, your rebuilt unit 1) will go right in, no worries and/or 2) will provide a nice unit to sell to another "S" owner should you and this Board come up with a satisfactory (and quite possible) better alternator for your car.

I agree, rebuild the old one. So many of the new replacements are just not the quality of the factory OEM.

The one sold as direct replacement by Pelican is Valeo with internal regulator. You can find external VR models for sale on Ebay for less than $200. I was stuck by the side of the road when I replaced mine in a motel room in Butte, so I had little time to shop around. The replacement with the Valeo unit is relatively easy. The thin black wire is left disconnected and the other three wires go where you think they should. The external regulator is disconnected. You need to cut the air deflector about half a centimeter along one edge to accommodate the internal regulator profile. I used a Swiss Army knife to cut mine but were I at home I would have used a Dremel tool. Why is your alt. light on when running? Have you figured that one out? 15.6 volts is high but it indicates your alternator is working. The voltage regulator is supposed to lower the exciter voltage to compensate which makes me wonder if you have a bad connection somewhere, maybe the blue wire at the 14 pin connector, pin 11. Good luck.

Targalid asks: I really don't know the answer but when we replaced the VR during a Porsche Trek last May it seemed to help for a while. By the time of our August Trek it was staying on and the voltage began to climb across the rpm spectrum. I keep reading in related posts that the diodes on the alternator frequently "burn out" and I am presuming that that is related to my problem.

I guess our sponsor doesn't rebuild alternators but we have a reputable auto electric guy in Missoula that probably could do the job.

Thanks for your suggestions, all, so far.

Tom

Rebuild the old unit. Take it to a reputable shop. They will analysis your, old one rebuild it ,to as good as, if not better than new. for half the cost of new. The old units are probably better built than the new of today.

Though most modern alternators have internal voltage regulators, I find it much easier to replace the external voltage regulator if it starts to go bad. Having done this on my 911 and 914-6, it's not one of my favorite jobs to tackle.

I have a '75 911S and went through this several years ago. Replacing the voltage regulator did not do any good. The original alternator seemed to be ok, but the light would stay on and especially at night with the headlights operating. I ended up replacing it with the Valeo offered by Pelican, and all has been fine since.

However, when the new alternator is installed and the old external regulator is disconnected, I believe this also disconnects the radio noise supressor next to it. I have often wondered if the noise supressor was causing the problems with my car.

1975 was a transitional year with the fan housing. The original alternator, at least in the early models that year, had the smaller housing. However the fan housing was designed for use with the later longer alternator. Porsche installed a spacer to allow the use of the smaller alternator in this housing. You will not need this spacer if you convert to the new alternator, or if you decide to find a later 911SC externally regulated alternator which had a higher output.

If you use a new alternator, there was a bulletin by Porsche which explained the wiring change. You will also have to cut a notch in the plastic vane behind the alternator to allow room for the internal regulator. Also, the fan pulley nut is a different size than original, so you will need to find a spare wrench of the proper size to keep in the car in case of a fan belt issue on the road.

Yep - First choice is rebuild with a quality shop.

While you have things apart and waiting for the rebuild, go through the engine wiring harness and verify that your wiring/connections are sound and that you have a good ground strap connection.

Always have your original rebuilt.

If you do decide to purchase a factory rebuilt make sure that you save the original. Twenty years from now those numbers are going to be a huge deal.

Richard Newton

rebuild as there are 2 sizes for the alternators depths and it took me a couple times to figure it out. Luckily I had the original and it rebuilt locally.
i also use an adjustable external voltage regulator.

Alt rebuild
 

Just in case you have any problems.Send it to me I have an Alt ,Starter rebuild shop in Ohio.Would be happy to rebuild and help anyone here .... Thanks

Russ Adams
Sagle Auto Electric
200 W.Monroe St.
Zanesville,Ohio 43701

Thanks guys. You all are the best.

My auto-electric shop in Missoula says he can handle it. I'll give him a chance in a couple of weeks. It just turned cold again here so will wait for the sun.

Tom

Turbo 951.

PM Sent

Tom

Is there no better replacement than rebuilding? I can see a 90A alternator getting pushed very hard with some lighting upgrades, heat/AC blasting, and an aftermarket stereo.

Maybe a modern replacement for the voltage regulator? Seems like that's a part that shouldn't be failing in the 21st century. On vintage motorcycles, we'd throw modern SCR series switching regulators from modern bikes, but that's for stators, not alternators...

I'm surprised nobody has rigged a cheap/good Chevy alternator up where the AC compressor bracket is...

Woo Hoo -- I have a lot of questions about alternators.

First one is what do you do about worn slip rings in an 88 (I think it is a Valeo) alternator


Sorry if this is a hijack