Alternator / Charging Question

[JShep]

84 944 n/a, 5 speed

started the car this morning and noticed that the charge warning light did not come on before I started.
Shut the car off and repeated the start - same thing, no charge warning light when the ignition was in the "on" position.

Car was running fine, so, of course, drove it to work.

About 1 mile from work, the engine started to die and the mpg meter went full scale to 40+ mpg.

As the car finally gave its last gasp, I was rolling into a parking place (yes, at work), it would not restart, all indications were that the battery was dead.
Windows would not go up.

Measured the voltage across the battery about 30 minutes later, and it was at 11.9v.
Was able to get the passenger window up at that time.
Charge light would again not come on in when the ignition was in the "on" position.

So the question is: Do I need the new diode / brushes pack and / or the "Condenser".

I did a quick search for previous threads on pelican and checked Clarke's, but was not able to accurately determine if others issues duplicated the symptoms that I have.

Any experience would be appreciated.

Thanks

[hpservertech]

By condensor you mean alternator right?

Have you checked to see if the belt is even still there? Dumb I know, but it has happened before.

Get the alternator checked by a place like autozone and go from there.

[ColoradoSteve]

The belt may still be there but it could be loose, I had a very similar experience. In my case the bolt was missing from the rear of the AC compressor ( 3rd pulley) which caused the belt to slip. These cars will not run without a full charge from the alternator and if you do have a bad alternator they're not that expensive and easy to replace.

[John_AZ]

Hello JShep,
I had the same experience last year. I switched batteries and got home. I took out the regulator on the alternator and saw the brushes were short-they need to be 5/16 inch or longer.
Check your regulator. Remove the air box and unscrew 2 screws that hold the regulator to the alt. If your brushes are short get a new one and replace. You should also "dress" or smooth the brush contacts/ring inside the alt.
If you want a really good DIY on alt rebuilding see:
http://forums.rennlist.com/rennforums/showthread.php?t=330417&highlight=alternator+rebuild

John_AZ
1988 924S + 1987 924S

[JShep]

Thanks for the input all.

Hope I can get home tonight, will not use the fan even though it is very hot here today!

Forgot to mention that the battery has given signs of being worked hard - it has vented some liquid on the battery area, so I plumbed the vent to a plastic bottle. Sure enough after the drive this morning, there was some liquid in this catch bottle.

Yes, I will remove and check the brushes, after I get home tonight.

Appreciate the help! Will provide a root cause when it is fully understood.

[hpservertech]

Your battery is venting out???????????

Get rid of the battery and get a new one.

[JShep]

Purchased a new brush diode unit, installed, still no charge system light when the key is turned on. Battery voltage when running - 11.3v - not good!
Removed gauger cluster and tested the charge indicator bulb - bulb was functional (hard to review the schematics from the Porsche shop manual)
Did a brief check of the ground points - no major issues uncovered.

Removed alternator, went to Autozone to have is tested (with the new diode pack) - all systems failed. (this test was for free - a great service!)

This led me to believe that there is an "open" in the windings of the alternator itself.

Purchased a used alternator (from a 924S) - great deal - $20. + shipping.

Installed the alternator, reconnected the battery, turned key to "on" position - bingo - charge light illuminated, YES!!!

Started the car - battery voltage is 13.4v with and without lights on, when fans are running it is down to about 13.1, still acceptable.

Learning from this adventure - any "open" in the charge system will cause the charge light not illuminating - means that the system is not functional and your running on just battery power - only for short distances, shorter when lights and fans are on.

I also had the battery tested at autozone also - this check out fine according to their tester.

Hope this helps others with similar issues.

[John_AZ]

JShep,
Nice work. Since you did buy the brush/diode for your original alternator, why don't you put it in the used one? Is brush/diode the same as what I called the voltage regulator? Clean the contacts as I suggested.
Now you have a spare voltage regulator and a fancy paperweight.

Thanks for the update.

John_AZ

[JShep]

John -

I like your ideas, and will be able to keep the brushes as a spare. The intent was to be able to ensure that the alternator windings was indeed the component that was problematic.

I had done a bunch of reading about these types of issues - one suggestion was to remove the ground strap from the battery, while the car was running, if it continues to run, the charge system is working, if not, the car is operating under battery power only.
In additional reading (as always, after the test was run), it was said that this test may ruin the diodes. So I was hesitant to put in the new brushes after this test. After all was done, in my case, since I believe that the windings of the alternator were "open" theree was no chance that the brushes / diode saw any electricity, thereeofre, they should be a good spare / quick replacement item.

Car is running well at this point! I did take the opportunity to change the timing and cam belt. There is a little belt whine, so I'll back off the balance belt next week.

Your comment about being able to turn the water pump by hand, when the cam belt is properly tensioned was interesting. I perofrmed this test out of sheer curiosity and ofund it easier than I thought. I didn't think too much about it at the time. My thoughts were that it was strange that the water pump is driven by the flat side of the cam belt only, but rationalized the design in my mind as that once the engine is running, there should be more force around the water pump pulley.

Have monitored cooling temperatures - no changes in function from before the belt replacement and no squealing. (water pump turned freely by hand with no belt)


Appreciate your insights - they have been very helpful.


Thanks

[John_AZ]

JShep
It is interesting that you were able to easily turn the WP pulley after the tension. I can do it with my thumb and two fingers but it is not easy-I need clean fingers and a bit of muscle.
I was corrected on the amount of aluminum expansion earlier. I have the spring loaded tensioner on both cars.

Information provided by:
DaveBoettcher

Whilst undeniably true, my 1980 copy of Machinerys Handbook gives the coefficient of linear expansion of pure aluminum as 0.00001244 per degree F. So if the block heats by, say, 80 C from rest to hot, this would give a linear expansion of 0.0017914, or about 20 thou in a foot. I don't think this is really significant, and would probably be less in aluminum alloy as used in engine blocks.

With this information, I prefer my tension to be slightly/cannot definitively measure/ tighter, but not so much that once the engine is hot the belt pressure will cause premature WP front bearing failure.

When finished, I take a palm branch and mumble a few words to the Porsche designers. I change my belts every 2 years. No matter what the mileage. $12 piece of mind.

Have a good weekend.

John_AZ