Alternator - power

Sonic dB · Sonic dB's Garage

Hi, I have some questions about alternators.

In Leffingwell's book (Porsche 911 Buyers Guide), he indicates that the alternators in the Carreras tend to die at an early age (40-70K miles). Im pretty sure that mine is original, and the car is at 77 K.

The tachometer has been bouncing since I purchased the car, which was 14K miles ago.... The car runs perfectly and seems to have plenty of juice. Im about to install some audio equipment into the car, including at least one mega-watt power amp.

Do alternators give any "signs" before they fail...or do they just tend to fail all together?

Would the bouncing-tach issue be most likely related to the alternator...and could this be a sign of potential failure?

Are there any steps or preventative measures to take, which would eliminate being stranded in the middle of nowhere with dead alternator and no way to get car running?

Thanks very much for your advice/opinions.

yelcab1 · 12-24-2003, 08:56 AM

no signs necessary

GrindingGears · 12-24-2003, 09:23 AM

"Do alternators give any "signs" before they fail...or do they just tend to fail all together?"

I have the same question...

ubiquity0 · 12-24-2003, 09:28 AM

Sonic- did you ever find the cause of your perceived lack of power, or was it a non-issue. Hardly related, just curious.

Do the headlights dim when revs drop? Other than that you should check voltage across the battery- plenty of posts about that.

rudy sanchez · 12-24-2003, 09:32 AM

mine was going slowly. it still provided some charge and I was never left w/ a dead battery.

my alt light would glow bright at idle and would go off at higher rpms. then it started to have a slight glow at higher rpm and I had it replaced before it failed. this is on a 71 911e, had the stock alt but on a fully rebuilt and modded 2.7.

it still had the old alt housing from the 2.2 so we had it machined to accept the larger output alt w/ internal regulator.

paul schuster
santa cruz

Sonic dB · Sonic dB's Garage

Quote:

Sonic- did you ever find the cause of your perceived lack of power, or was it a non-issue. Hardly related, just curious.

No...Im still not completely satsified with the acceleration. However the car was weighed down with my sales stuff when I did those "tests". Im thinking about getting one of those G-Force things to see if its more accurate.

On a related note, the car did run erratically last month....just before the DME relay died. So, it was giving me signals that it was going, then died all of a sudden.

Right now, everything is good...but my instincts tell me that the next failure will be the alternator...and Im concerned about possibly overtaxing it with the addition of the audio power amps.

RoninLB · 12-24-2003, 09:51 AM

Quote:

Originally posted by Sonic dB

alternators in the Carreras tend to die at an early age (40-70K miles).

Do alternators give any "signs" before they fail...or do they just tend to fail all together?

Are there any steps or preventative measures to take,

from reading Loren & John Cramer, it's the heat that cooks the internal reg. External reg are more reliable.

you may get a foreboding. I think it could be tach problems, but don't have hard info close for that.
I installed a volt gauge.

and I just changed a good internal regulator for a brand new one because I was in that area for other stuff. I'll keep the good 40k mile used one in the luggage comp.

ubiquity0 · 12-24-2003, 09:57 AM

Quote:

Originally posted by Sonic dB
No...Im still not completely satsified with the acceleration. However the car was weighed down with my sales stuff when I did those "tests".

What do you sell? Acme anvils?

When I get my SC's warm running issues somewhat sorted I'm going to dyno it. Just HAVE to know that the car is running at its potential.

singpilot · 12-24-2003, 09:58 AM

My bouncing alternator was the ign wires 'telegraphing' the light show that was occurring in the engine compartment. Replaced the wires, no more prob.

nostatic · nostatic's Garage

my lights will pulse, with voltages swinging between 13 to 15V. I think my alternator is going, as I replaced the (external) VR. It bench tested OK, and only happens when first starting the car. I'm taking it as a sign...

singpilot · 12-24-2003, 10:11 AM

You want to know if your SC is running at it's full potential??????

Come on a fun run here in SoCal. By the end of the run, you'll know.

I got 2 Ferrari passes in the same day.

Merry Christmas everyone!

nostatic · nostatic's Garage

Quote:

Originally posted by singpilot

I got 2 Ferrari passes in the same day.

Yeah, but wasn't that just Wayne? Kinda like kissing your sister

singpilot · 12-24-2003, 10:18 AM

But if still felt good.. haha.

Actually, it is a pretty good guage of how yours is doing. Find another SC and stay with him, or him with you. You'll get a feel.

BTW, mine does as advertised. I am really happy with the front brake cooling ducts, I had noticebly less fade in the fast part of the canyon this year.

Sonic dB · Sonic dB's Garage

Its not the ignition wires, I put new Magnecores on there this summer and the tach still bounces.

Maybe its a problem with the tach itself?.... it actually looks like it is NOT the original tach, as the black inside the glass is slightly faded and the tach obviously has been removed before because it is not seated into the hole very well and can be pulled out easily....hmmmmmmmm

RoninLB · 12-24-2003, 10:28 AM

Quote:

Originally posted by Sonic dB

Maybe its a problem with the tach itself?....

I don't know much about the DME but,
in days of old, the CD box has a tach output from a seperate circuit.. so I would figure that any current feed interference for the CD box would interfere with the tach signal....

911SC Pilot · 12-24-2003, 10:45 AM

I dont have the listed above problems.,.,.,.,.,but I do have a problem myself. Ive noticed latly, that when I tun my lights on, I hear a winding type sound. Only happens when I turn the headlights on. If I just have the parking lights, or no lights, there is no winding sound. Would this be a alt problem on my end.

Also, my speedo has a thing about not working until A: I get passed 40mph, or, if I tap the glass, it works.,.,.., whats the cause ?

TerryBPP · 12-24-2003, 10:56 AM

Sign that your alternator is going:

1. Surging headlights and interior lights. Also could be VR.
2. Low voltage reading between posts on battery. Should be around 14.5V. Mine was at 9V when it finally died.
3. Obviously a repeated dead battery.

Consult John Cramer, he help me out tremendously.

Steve W · Steve W's Garage

Sonic, those alternators in the Carreras typically fail around 75k miles or so most often due to the brushes being worn out to the point that they no longer contact the commutator. When they no longer contact, the battery doesn't get charged either, and you keep driving until you run your batter out and wondered what happened. This has happened to me quite a few times over the course of two Carrera's I've owned over the past 19 years. The solution was simple. Take the alternator out and drop it off at a local starter/alternator rebuilder. They replace the brushes and turn the commutator, and everything is as good as new. Total cost: about $55

Sonic dB · Sonic dB's Garage

Good info, thanks Steve W.

In preparation or preventative maintanance....would it make sense to carry a spare battery up front to use in case the alternator fails and battery drains down when Im on the road far from home?

RoninLB · 12-24-2003, 01:49 PM

Quote:

Originally posted by Sonic dB
In preparation or preventative maintanance....would it make sense to carry a spare battery up front to use in case the alternator fails and battery drains down when Im on the road far from home?

from above,
"I installed a volt gauge."