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alternator replacement

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Hello. When I start the engine the volt meter shows about 10 volts during cranking and 14 volts just after the engine starts. Within minutes the voltage slowly drops to 13 volts then more slowly to below 12 volts (after, say 15 minutes). I thought the battery may have had a bad cell. However, installation of another, sound, battery shows the same symptoms. Thus, I plan to replace the alternator.

The NAPA Auto Parts website lists several alternators for my model (2002 C2, 6-speed). I can eliminate those for automatic transmissions. The remaining units have either the 6-rib pulley or the 6-rib clutch pully. My car has the clutch pulley.

Can the clutch pully slip causing the alternator to rotate more slowly and generate less voltage? Can the clutch pulley be replaced by itself? Can the clutch pulley be locked or pinned? What is the purpose of the clutch pulley?

Any advice will be appreciated.



Edited by cyclocross
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Check out this thread regarding the pully.

Check out this thead regarding the low voltage situation.

In short, if the battery is fine - remove the alternator and have it bench tested at Napa before replacing it. It could be a bad voltage regulator, the alternator could indeed be bad, or you could have corroded wire somewhere given the age of the vehicle in question.

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logray, thank you for the links. I have inspected all of the cables except the ones connected to the alternator. I have even loosened their nuts and wiggled their clips to obtain a better metal-to-metal connection. All the connections look good with no corrosion. It is interesting that the clutch pulley manufacturer states that the pulley should be replaced at 90,000 kM (per RFM's post in the first link).

Tonight I'll check if there is any slippage with the clutch pulley (my last gasp before removing the alternator).

Have any of you folks experienced a pulley failure or replaced it?

Thank again.

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Excessive current over time can cause internal resistance which you can't see but can only measure. As these vehicles age we are starting to see more problems with the positive and grounding circuits.

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Dan, I assume that when you are checking the voltage with the engine running, you are spinning the engine above 1500 rpm. The alternator will not give out a decent charge @ 800 rpm idle speed.... If the voltage is still low I would replace the alternator as your cars electonics rely heavily on a healthy charging system..

Regarding the clutch pulley. My 2001 Boxster S (74,000 km) had a rumbling noise at idle, this was about 2000 km after fitting the Raby underspeed pulley and new belt. I removed the belt and ran the engine quickly without it - the noise disapeared. I got out my trusty medical stethoscope and located the rumble coming from the upper belt pulley, so I removed all the pulleys and replaced the bearings, bolted everything back up - and the noise was still there !!!! ****......

So it could only be either the alternator or the power steering pump, and as the alternator was easier to remove, I took it out and checked the shaft bearings - all looked OK but I took it to my Bosch agent who diagnosed immediately a semi siezed clutch pulley. You need a special tool to remove the pulley from the alternator shaft, but it only takes a minute. Once a new pulley was installed the noise has completely gone, The Bosch agent says these clutch pulleys seem to always sieze rather than slip and cannot be repared.

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Well troops, it was the alternator. I installed a new (refurb.) unit last night and all is well. The voltmeter registers just under 14 V. It is probably my imagination but the car seems to run better (and the sky is bluer, the grass is greener, etc.) I followed Loren's DIY which was indispensable.

One comment on the DIY. Step 7 states gentle tapping on the right side bolt to push back the threaded insert. Gentle tapping - HAH. This was the hardest part of the installation. It must have taken me 45+ minutes of whacking the bolt or the insert and using penetrating oil to get the insert to move. Once the insert had moved about 1/16" the old alternator came out as easy as could be. The new unit had a slightly greater space between the two right side lugs and it practically walked itself into position.

All-in-all I was very satisfied in the repair. When one first looks at the alternator one asks how on earth can it be removed. However, once the air filter box is removed there is now plenty of room for the repair - just mind the little hoses and the o-ring as Loren cautions.

Enjoy the 4th!

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  • 3 weeks later...
  • 5 months later...

Hi folks,

Well, for the first time in years my porker gave me some trouble this weekend. Noticed the amp/volt meter randomly dropping and picking up and then finally it dropped out. All sorts of lights came up on the dash. It was nighttime and I had to limp home on the battery power but eventually even that gave up. So I had to get the AA to flatbed me home. The AA tested my battery and said it was good. He also did some tests on the alternator. Said it was reading about 13.7 at about 1500 revs. Said it was not marvelous but still should not be a problem. I am fairly convinced its the alternator but there are some oddities:

* I noticed when the alternator faied, if I revved the engine hard with a quick kick, the alternator kicked back in but then failed again later.

* I also thought I saw the alternator fail and kick back in when I hit bumps in the road.

* This is the first time I have taken the car out this winter after hibernating for 4 months. The battery was dead, I boost started it and drove 40 miles thinking I could charge it. Was this enough time to charge?

So anyway, me thinks I may have a faulty or corroded connection somewhere.

Anyway, I took the car to my local Porsche service center. They want, get this, £975, plus 20% VAT to fit a new alternator. Sheesh! So I am seriously thinking of doing the job myself with Lauren's DIY instructions.

My Question, for a lowly computer geek who can be dangerous with a few spanners (wrenches), is this really a DIY job or should I just cough up mullah to have it done professionally?

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Sounds like you have a failed brush in the regulator which can explain the intermittent charging. It's an easy DIY and be sure to use a battery charger to fully charge the battery and not let your new alternator try and do the job.

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Sounds like you have a failed brush in the regulator which can explain the intermittent charging. It's an easy DIY and be sure to use a battery charger to fully charge the battery and not let your new alternator try and do the job.

Got the alternator out following Loren's "fair to moderate" DIY. Sorry Loren but it isn't clear from the instructs which bits are what. The diagrams have arrows to bits but no explanations as to where they are exactly . To the home DIYer it would be helpful to know which is the belt drive pully, vacuum switchover valve, etc. I did figure it out in the end but to be honest I would have had the alternator removed in literally 15 minutes if I hadn't had to scout around to figure which bits are which in the instructs. Just a bit of constructive feedback Loren. Anyway, in the end it took me about 45 minutes. I didnt have an alerminium mallet so I used a piece of hardwood and jammed it between the holding arm and alternator and prized it apart extremely easy. Also, I dd manage to fairly easily get the alternator off the holding arm COUNTERCLOCKWISE. The instructions say the alternator must be removed by turning it clockwise towards the crank case but it just would not move that way. The wood prizing took it the opposite way extremely easily then I simply pushed the alternator back, turned it so that the left attachment arm was free of its fixing and pulled the unit out. It is extremely tight but it is possible and personally I think easier this way.

OK, so now I have it out, are there any instructions on how to inspect the brushes. I turn the spindle and it seems extremely silent. I dont hear any brushes at all. Based on the fault, this is what I am suspecting.


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