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Alternator Troubleshooting and Replacement
 
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Pelican Technical Article:

Alternator Troubleshooting and Replacement

Time:

4 hr

Tab:

$65 to $300

Talent:

**

Tools:

Hex key set, wrenches, 911 pulley tool

Applicable Models:

Porsche 911 (1965-89)
Porsche 930 Turbo (1976-89)

Parts Required:

New alternator brushes or a rebuilt alternator, new alternator belt

Hot Tip:

Replace the brushes and check the electrical grounds before you replace the alternator

Performance Gain:

Higher charging output

Complementary Modification:

Clean/Paint the fan, Upgrade the fan to 11 blade type
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

One of the nice things about the configuration of the 911 engine is the relative ease with which you can replace the alternator. The alternator is located directly in front of the fan: a great location because of the amount of cooling air it receives. The replacement and repair process is straightforward, and should take you about an afternoon to complete.

The first thing that you need to do is to make sure that your alternator is indeed the cause of the problems with your charging system. Sometimes bizarre electrical problems can be caused by a number of faults other than the alternator. It's important to troubleshoot the system prior to replacing your alternator.

The first thing to check is the fan belt. Is it tight and amply turning the fan? If not, then retighten it, according to the procedures outlined in Pelican Technical Article: Fan Belt Replacement. Modern fan belts rarely break, but they get brittle and glazed with age, and can slip on their pulleys. Replace it with a new one.

The next item to check is the voltage at the battery. This should read a little more than 12 volts with the engine off. When the car is running, the voltage should read at in the range of 13.5 to 14.5 volts with the engine at 2000 rpm. If your battery appears to be leaking, then your voltage regulator has probably failed. The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 16 or 17 volts, then the regulator is probably bad. If your battery has boiled over and has acid overflowing out the top, make sure that you clean up any spilled acid immediately. Dousing the area with a water and baking soda solution should help considerably to neutralize the acid, and prevent it from eating away at the metal.

The following guidelines are useful for troubleshooting your alternator:

  • Alternator indicator lamp is on with the ignition key off.
  • Alternator has failed, and diodes have shorted out. Replace alternator and in the meantime, disconnect battery to prevent it from becoming completely drained.
  • Alternator indicator lamp does not light when ignition key is turned on.
  • Alternator bulb has burned out.
  • Regulator has failed
  • DF wire is disconnected or broken from alternator
  • Alternator has failed, and internal windings are open
  • Indicator lamp remains on after engine is started and running above 2000 rpm
  • Regulator has failed
  • Battery lead to alternator has been disconnected
  • Alternator is not firmly grounded
  • Alternator internal bushings are dirty or worn
  • Alternator is bad
  • Indicator lamp is dim after starting, and gets brighter as engine rpm increases.
  • Battery lead to alternator loose or bad
  • Ground connections are bad
  • Battery is bad
  • Alternator is bad due to open diode failure
  • Indicator lamp is dim after startup, but eventually gets dimmer and goes out when engine RPM increase.
  • Low charged battery
  • Poor connections to battery
  • Indicator lamp is dim after startup, and gets dimmer as rpm increases, but never goes out.
  • Regulator has failed
  • Alternator is failing

An important item to check on your car is the transmission ground strap. The engine is electrically isolated from the chassis by rubber motor mounts. If the transmission ground strap is missing or disconnected, then you might have a whole bunch of problems, including electrical system malfunctions and difficultly turning over the starter. See Project 87 for the exact location of the transmission ground strap.

All 911s up to 1981 had external regulators and from 1982-on, the alternators had built-in ones. If you've determined the regulator to be working properly, then you should probably remove the alternator for testing and inspection. Before starting any work, make sure that you disconnect the battery. The positive battery terminal is directly connected to the alternator, and it can be dangerous to work on if it's live.

The first step is to remove the fan belt. Refer to Project 3 for detailed instructions on the fan belt removal. Removing the fan housing itself is a very easy process. The entire assembly is affixed to the engine case by a metal band that is tightened around the fan. Loosen this band by removing the one or two large cap screws that secures it. There should also be two nuts that secure the coil, and a few fiberglass shroud screws that need to be removed. Once the assembly is loose, the fan can be pulled away from the engine far enough to access the nuts and electrical connections in the rear. Be careful not to pull too hard, because the wires that are connected to the alternator are not very long.

Once you have access to the rear of the fan, remove the plastic air flow guide that surrounds the alternator. You should now have enough access to disconnect and remove the wires from the rear of the alternator. Make sure that you mark them, and/or take a picture of the entire assembly so that you know where each wire goes when it's time to reconnect them. You can destroy your alternator, and portions of your car's electrical system if you hook the connections up improperly. Also make sure that the alternator was properly grounded to the engine, as this can cause it to malfunction. The ground strap is a thick copper cable that connects the housing of the alternator to the engine case. Disconnect this ground strap before attempting to remove the alternator.

After the alternator is disconnected electrically, you should be able to remove it along with the fan assembly from the car. The fan is pressed onto the alternator (ultimately held on with the pulley nut) and the alternator is bolted into the fan housing. If you are planning on replacing just the brushes on the alternator, then you can remove them now without removing the alternator from the housing. On a side note, almost every Porsche parts diagram has the brushes mislabeled as a 'support.' There must have been something lost in the translation from German!

Remove the brushes by unscrewing the small assembly from the back of the alternator, and inspect them to see if they are significantly worn. If so, then replace them (they typically cost about $50). If you think that you need to replace your entire alternator, then gently tap it out of the housing with a soft hammer. The fan is pressed onto the shaft of the alternator, and needs to be gently removed. Don't bang on the alternator shaft too heavily, as this may damage the bearings inside.

The installation of the new alternator is simply the reverse of the removal process. Make sure that you reconnect all of the wires to their proper terminals when you are done.

In 1975, Porsche implemented a five-blade fan instead of the normal 11-blade one on all the 911 motors. The purpose of this fan was to provide less cooling to the engine, forcing it to run hotter. This was accomplished solely for the task of meeting emissions requirements. The hotter the engine, the better the gases burned, and fewer emissions were produced. However, this didn't help the longevity of the engine. These engines overheated easier, and generally lasted significantly less than their predecessors. One upgrade that should be performed on every 2.7 liter motor is the replacement of the original five blade fan with an eleven blade one. The two fans are interchangeable, and can be switched when replacing or removing the alternator. The only other part that may need to be replaced is the pulley half - it must be matched specifically to the size of the fan. Also, different sized fans and pulleys used different length belts: make sure that you get the one that's appropriate for your setup.

The alternator is attached to the fan and the fan housing.
Figure 1

The alternator is attached to the fan and the fan housing. The housing is strapped to the engine case using a long metal strip that needs to be loosened and disconnected before the housing can be removed. Remove the coil and the few select screws that attach the fiberglass engine shroud to the fan assembly. The long metal strap does not need to be completely disconnected from the case: leave it attached to the case at the bottom.

Once the housing is disconnected from the engine, remove the rear cream colored plastic air guide that surrounds the rear of the alternator.
Figure 2

Once the housing is disconnected from the engine, remove the rear cream colored plastic air guide that surrounds the rear of the alternator. This piece is held on with nuts that are attached to studs located on the alternator. Be careful not to crack this piece when you are reinstalling it. Using too much torque on the nuts can easily damage the air guide upon reinstallation.

Carefully label and disconnect the connections to the alternator.
Figure 3

Carefully label and disconnect the connections to the alternator. Remove the large, thick ground strap as well. Be aware that the wires are quite old, are subject to heat from the engine, and may be more brittle than you would think. Try to avoid moving them around or bending them too much. Inspect the connectors carefully, and replace any that look damaged or rusted. Double check the wires upon reinstallation. It's very important not to confuse and mix up the terminals to which the wires are connected.

The alternator should slide out of the housing.
Figure 4

The alternator should slide out of the housing. It may need some gentle coaxing, but be careful not to damage the studs that mount it to the housing. Some light taps with a soft hammer should force it loose from the housing. Try to tap evenly around all of the studs: it's easy for the alternator to get jammed inside the fan housing.

The fan is pressed onto the alternator shaft, and requires a bit of effort to remove.
Figure 5

The fan is pressed onto the alternator shaft, and requires a bit of effort to remove. Don't use too much force in prying the fan off, or the bearings inside the alternator may become damaged. If you have any doubts, take the fan to your local machine shop and have them use a press to remove it. Now would be a good time to upgrade to the 11 blade fan if yours doesn't have one already installed.

Some of the 911 alternators have brushes in the rear that can be easily removed and replaced.
Figure 6

Some of the 911 alternators have brushes in the rear that can be easily removed and replaced. Remove the brushes and inspect them carefully if your alternator is not working well. If the contacts are as short in length as they are in the photo (shown by arrow), then they are worn and need to be replaced. If they are long, then you probably have some other internal problem with the alternator that is causing it to malfunction.

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Comments and Suggestions:
spagbol23 Comments: Hi. I have a shroud from year 1984-86 casting number 930.106.102.3R. It had an SEV Motorola alternator which i am presuming is not original part due to external regulator which i want to replace. What alternators with internal regulators will fit that shroud? OEM number would be helpful.
November 9, 2016
  Followup from the Pelican Staff:

I’m not the best with part numbers and do not PET.


Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.


- Nick at Pelican Parts
 
malcolm Comments: I successfully replaced the Valeo voltage regulator & brushes from the rear of an alternator on a 1989 Porsche 911 Carrera without completely removing the alternator or wires. However, I cant engage the mounting strap the space between the strap ends is too large for the cap screw to engage. I think the alternator is not seating properly and is sitting too high, maybe about 0.5 inches. How can I seat the alternator so the strap ends come closer together?
June 22, 2016
  Followup from the Pelican Staff: Try rotating the alternator to get it to drop in further. It's possible it is out of alignment from your repair. Worse case,remove the alternator and reset the installed position.- Nick at Pelican Parts  
orlando Comments: good day , my 81 911 sc up to 2000 rpm no noise but above some steady noise likely from alternator bearing...is possible ??? thanks for help
March 22, 2016
  Followup from the Pelican Staff: Yes, very possible. Take the belt off, then check if the noise is present when spinning the alternator by hand. - Nick at Pelican Parts  
Travelin Man Comments: Nick, It had 5 shims in the box.
December 7, 2015
  Followup from the Pelican Staff: The shims go with the belt pulley to add or remove tension to the belt. - Nick at Pelican Parts  
Travelin Man Comments: Working on a 1970 911T
December 7, 2015
  Followup from the Pelican Staff: Thanks. - Nick at Pelican Parts  
Travelin Man Comments: MY question is about the brass shims that where on the alternator. The engine was all apart when I got it and these brass shims where in a box with the alternator and I see no logical place for them. Any info on this?
December 3, 2015
  Followup from the Pelican Staff: What vehicle are you working on? - Nick at Pelican Parts  
Bizdoc6 Comments: I have a '79 911 sc. no where do I see in the articles what to do with the old outside regulator? Do I take it out or does wrapping up the old black connector disconnect the old regulator completely. Thanks Donaldspent 2 yrs re-doing my 911 and don't want to ruin the wiring
July 28, 2015
  Followup from the Pelican Staff: If using an alternator with an internal regulator, the external is removed. I don't think we have a procedure for that right now. I looked around for it. - Nick at Pelican Parts  
doug996 Comments: Hi Nick, further to your discussion with 'tonybuono' regarding reconfiguring the wiring from the older type alternator to the Valeo, I was hoping you could clarify something here. I have a 1980 911sc and I am currently replacing the older style alternator with a new Valeo. The wiring removed from my old alternator was Red B+, Blue +61, Brown spiral to D-, brown D- there are two connections marked 'D-'and black to the spade contact on brushes. My question is, what happens to the brown and brown spiral wires, do the both connect to the D- as shown on the technical bulletin supplied by Pelican?
June 30, 2015
  Followup from the Pelican Staff: Looks like they go to D-.

See attached. - Nick at Pelican Parts
Frank Comments: '89 911 3.2 liter. Voltage is REEEALLLY low! Cant believe car even starts. Battery shows 10.8v when car off, 10.0 when car on and accessories on. Revving even to 3000rpm does not increase voltage at all. Battery light flickers on and off. Battery is 3.5 years old, Alternator is 17 years old. Time to replace alternator, I assume? What's the right part # for this car?
February 26, 2015
  Followup from the Pelican Staff: http://www.pelicanparts.com/catalog/SuperCat/0826/POR_0826_ELCHRG_pg1.htm #item0

This link is for alternator choices for the 3.2L Carrera, don't forget to buy a belt while you're at it!! Make sure you inspect the fan housing mounting points VERY closely for deterioration and cracks. If the housing is cracked replacement is recommended. Another sign of bad fan housing is scratches inside the fan housing from the fan/alternator assembly scraping the fan housing. - Casey at Pelican Parts
 
Buke Comments: Correction, I have NOT removed the ALT,yet. My 964 has 107K miles on it. All equipment is original. Thanks again.
August 27, 2014
  Followup from the Pelican Staff: Got it,. thanks. - Nick at Pelican Parts  
Buke Comments: Hello everybody!
Looking for thoughts, suggestions, or past experience, "Oh yeah I know what that is..."
My 1990 964 has an audible tone going on, beeping that is. Alternator light is not on. Battery load test is good. The battery is at full charge. With the engine running at 2.0KRPM, VDC measured at the battery is 13.5VDC or lower with no load, with load VDC is less. I have removed the ALT or have checked grounds. I have cleaned battery posts. Just looking to cut to the chase, so to speak,
Thanks in advance.
August 27, 2014
  Followup from the Pelican Staff: You could have high A/C voltage from the alternator. I would check it. No more than 0.5 volts a/c. - Nick at Pelican Parts  
tonybuono Comments: Excuse me. The brown wire goes to the terminal shown in the upper left of the photo.
August 21, 2014
  Followup from the Pelican Staff: Thanks - Nick at Pelican Parts  
tonybuono Comments: I sent this into to Valeo Services:
With the info you sent, which is a similar configuration although flipped from right to left, I successfully installed the alternator. The part is Valeo 101822, 55Amp w/internal regulator, Porsche part 901 603 120 06.

As you can see from the photo of the Valeo alternator, only three wires are connected. The black wire to the spade connector on the old alternator brushes is eliminated. The red 12V goes to the B30+ terminal upper right of photo. The brown ground goes to the terminal in the upper right of the photo unmarked but the D- terminal non-the-less. The terminal 61/D+ is the terminal in the bottom right of the photo. In most cases and according to the 911 wiring diagram a red wire leads to the external regulator, which has a blue wire to the tach. Disconnecting the red wire in my case it is a light tan wire with a spiral marker because of being rewired from a 912 to a 911 in 1970 from the external regulator and ensuring it is connected to the blue wire to the tach will provide the proper connection for the Valeo internal regulator to the tachometer.
August 20, 2014
  Followup from the Pelican Staff: Thanks for sharing this with us. How did the final set up work out? - Nick at Pelican Parts  
tonybuono Comments: Second photo on the same issue. The Valeo alternator.
August 19, 2014
  Followup from the Pelican Staff: Thanks, got it. - Nick at Pelican Parts  
tonybuono Comments: I'm replacing the alternator with external regulator in a 1969 911 with a Valeo with internal regulator. The wires, red B+, brown D-, light tan with spiral stripe D+/61, and black to the brushes. On the Valeo, the red goes to B+. Does the brown go before or after the black flat capacitor? I understand the black wire to the brushes should be terminated.? What about the light tan spiral striped wire the goes to the external regulator? How do I by-pass. One photo is attached. The second photo follows in my next comment.
August 19, 2014
  Followup from the Pelican Staff: Sounds like you go tit worked out before i got to your question. Here is your reply, I am sure it will help someone in the future: With the info you sent, which is a similar configuration although flipped from right to left, I successfully installed the alternator. The part is Valeo 101822, 55Amp w/internal regulator, Porsche part 901 603 120 06.

As you can see from the photo of the Valeo alternator, only three wires are connected. The black wire to the spade connector on the old alternator brushes is eliminated. The red 12V goes to the B30+ terminal upper right of photo. The brown ground goes to the terminal in the upper right of the photo unmarked but the D- terminal non-the-less. The terminal 61/D+ is the terminal in the bottom right of the photo. In most cases and according to the 911 wiring diagram a red wire leads to the external regulator, which has a blue wire to the tach. Disconnecting the red wire in my case it is a light tan wire with a spiral marker because of being rewired from a 912 to a 911 in 1970 from the external regulator and ensuring it is connected to the blue wire to the tach will provide the proper connection for the Valeo internal regulator to the tachometer.
- Nick at Pelican Parts
 
tonybuono Comments: I'm trying to replace my alternator 1969 911with a Valeo. As others on the forum, my wiring is different. I have a red wire to B+, a tan spiral striped wire to D+/61 to the external regulator, a brown wire to D-, and black wire to the brushes. From what I've read, the black connection should be cut. On the Valeo, the red wire goes to the + terminal. Should the brown wire go to the ground before or after the capacitor? Where does the tan spiral stripped wire go it was on D+/61? In other words, how do I by-pass the external regulator?

August 19, 2014
  Followup from the Pelican Staff: Sounds like you go tit worked out before i got to your question. Here is your reply, I am sure it will help someone in the future: With the info you sent, which is a similar configuration although flipped from right to left, I successfully installed the alternator. The part is Valeo 101822, 55Amp w/internal regulator, Porsche part 901 603 120 06.

As you can see from the photo of the Valeo alternator, only three wires are connected. The black wire to the spade connector on the old alternator brushes is eliminated. The red 12V goes to the B30+ terminal upper right of photo. The brown ground goes to the terminal in the upper right of the photo unmarked but the D- terminal non-the-less. The terminal 61/D+ is the terminal in the bottom right of the photo. In most cases and according to the 911 wiring diagram a red wire leads to the external regulator, which has a blue wire to the tach. Disconnecting the red wire in my case it is a light tan wire with a spiral marker because of being rewired from a 912 to a 911 in 1970 from the external regulator and ensuring it is connected to the blue wire to the tach will provide the proper connection for the Valeo internal regulator to the tachometer.
- Nick at Pelican Parts
 
kremer#2 Comments: Forgot where the third brown grpund strap goes. Two go on the alternator, and a third short strap goes ???
July 27, 2014
  Followup from the Pelican Staff: What vehicle are you working on? - Nick at Pelican Parts  
William D Comments: My 1969 912 generator just lost a copper contact and broke the brush on the bottom. It threw the contact into the bottom cover and it was hot enough that it melted into the plastic. The next contact after the ripped out one was bent. Things looked melted inside. What could have caused this?
February 20, 2014
  Followup from the Pelican Staff: Wear and tear along with time. The parts may have failed from use. I would replace what is broken. Then once running, inspect the generator to be sure everything is OK. - Nick at Pelican Parts  
BJ Comments: My alternator lamp is intermittent in my 1980 SC. The alternator lamp will go out after starting or might come on dim and get dimmer with RPM increase however my battery has never gone dead and the alternator is charging....????
I have an external regulator. Help!
January 27, 2014
  Followup from the Pelican Staff: Sounds like the alternator or the regulator is beginning to fail. Perform a charging system test to determine if that is the case. - Nick at Pelican Parts  
Rich Comments: 1974 911S Charging Problems

Alternator light on? Only showing 12 volts at the battery? Pulled the alternator 5 times only to have all the shops tell you its OK? Everyone wants you to replace the alt with an internal regulator type? Try this 1st: I assume you've done all the things in all the other articles like, cleaning, check the belt and connections, try another voltage reg. etc... use just the stock bulb without the socket, bend the little wire leads away from the glass bulb and connect to car wiring using small clip leads...my alternator then charged fine. If you don't have mini clip leads you can rig a temporary test with any 2-4 watt 12v test lamp. I had tried 2 other socket/bulb combos from my car but they didn't help. Then began a 2 year ordeal. I gave another socket a good cleaning and it's been charging ok. I can't believe I had several dirty sockets yet all the bulbs were operating ok, and no charge, very weird. Been fine for months now even after long sits. The "small bulb" sockets that Pelican sells 999-632-009-10-OEM are not for the "all glass" 1.2 watt bulbs Pelican 900-631-132-90-M97 in the older cars I found out the hard way these are for the push and twist bulb which is a better set up any way, and that is what I am now using. You can get the bulbs at any parts store. They are Wagner 11009 or a #3898 @ 2 watt/.17 amps 12Volts X Amps = Watts.
November 29, 2013
  Followup from the Pelican Staff: Thanks for the Info. We appreciate it. - Nick at Pelican Parts  
Mysterrob Comments: Need help with wire placement for my 83 911 with a Bosch alternator. Lost my diagram for reinstallation.
October 24, 2013
  Followup from the Pelican Staff: Red goes to B+

Brown goes to D-

Blue D+ - Nick at Pelican Parts
 
NYNick Comments: My belts keep breaking, although the alternator 'sounds' ok when spun with the belts off. We used OEM belts, twice, in 100 miles. Bearings bad, but no noise?
September 7, 2013
  Followup from the Pelican Staff: The alternator could be siezing or binding during operation. Check if the fan blades look like they are coming in contact with the shroud. If they are not, the belt may be too tight. - Nick at Pelican Parts  
frannyB Comments: Hi There,

Is it possible to remove and replace the bearings? My alternator seems to charge just fine, but the bearings feel rough.

Thanks, Franny
March 22, 2013
  Followup from the Pelican Staff: I would suggest replacing the laternator. If the bearings are worn, other parts of the alternator are likely work as well. Witht hat said, once the bearings are removed, you can replace them with the same size and specification sealed bearings. - Nick at Pelican Parts  

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