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Alternator Repair or repalcement

 
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pmcaya2  



Joined: 24 Nov 2005
Posts: 181
Location: Scio, NY USA

PostPosted: Wed Oct 25, 2017 12:09 am    Post subject: Alternator Repair or repalcement Reply with quote

Looks like I need to replace or repair the alternator on my '82 924 NA after around around 198 K miles. Gave it a new battery and had to jump start it, etc. Some questions:

1) any fuses or breakers I should check
2) is voltage regulator part of the alternator
3) will probably bench test at auto store
4) is it repairable with new brushes/diodes if coils and bearings are OK
5) any recommendations on OEM replacement or a compatible after-market off the shelf alternator?

I'm putting it in the garage for the winter, but I'd like to work the problem now. I owe it some TLC in the spring.
Thanks in advance for your response - Peter
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Eric P  



Joined: 21 Jun 2017
Posts: 94
Location: NY, USA

PostPosted: Thu Oct 26, 2017 12:16 am    Post subject: Reply with quote

1) any fuses or breakers I should check

There are no fuses or breakers on the charging system. Check your ground strap though! They have a bad habit of corroding or breaking.

2) is voltage regulator part of the alternator

The alternator I bought came with the voltage regulator. I believe it's part of the brush assembly. Note that there is a noise reducing capacitor on the back of your alternator. Most new alternators don't come with this. Save your old one.

3) will probably bench test at auto store

This isn't a bad idea. My local auto parts stores require the car to be running and the alternator to be installed in order to test it.

4) is it repairable with new brushes/diodes if coils and bearings are OK

Possibly? It depends on what exactly is wrong with it.

5) any recommendations on OEM replacement or a compatible after-market off the shelf alternator?

When I replaced mine earlier this year, I bought a rebuilt Bosch alternator. My local auto parts store had a 75A alternator for $64. You need to save the pulley, noise reduction capacitor (looks like an ignition condenser on the back of the alternator), the cooling shroud, and all the mounting hardware. Note that the original alternator mounts are rubber. If you're removing the alternator, replace the mounts. I believe Porsche updated their part to a plastic bit as the rubber was failing over time. Mine were rubber and had the consistency of chewing gum. I skipped a step and turned a couple aluminum bushings on my lathe so I'll never have to worry about it again.

While you're in there, there are a few other parts to replace. Replace the belt. You have it off already. It's easier to just do it now. Replace your ground strap. Due to those pesky rubber bushings, the alternator doesn't ground to the alternator mount. I think my alternator failed due to a broken ground strap. Inspect your power wires, replace as necessary. Also inspect your engine mount damper. It's bolted to the engine block behind the alternator. Mine had snapped and took my alternator ground strap with it. I ended up making a new damper mount.

Some people upgrade their alternators while they're in there. Bosch makes a 90A alternator that I believe bolts right in and I've seen people make new alternator mounts to put in huge GM alternators. I stuck with the stock 75A because it was cheap, easy, and I've never found the 75A to be too small... maybe upgrade it if you have a big amp or something? For me, it wasn't worth the $40 cost difference.

I will note that even with a rebuilt stock alternator, the voltage regular was slightly larger and didn't fit under the shroud on the back of the alternator. I used some "gentle persuasion" with a ball peen hammer to make the original shroud fit over the new voltage regulator. Once I made a small dent in the shroud, it bolted together without further issue.I wouldn't recommend ditching the cooling shroud like some people have. If your alternator is pulling hot air from the exhaust area, it won't live very long. The factory shroud pulls cool air from behind the bumper at the front of the engine bay to cool the alternator.
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1980 924 NA, US model
1987 924S, US model
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pmcaya2  



Joined: 24 Nov 2005
Posts: 181
Location: Scio, NY USA

PostPosted: Thu Oct 26, 2017 12:17 pm    Post subject: Reply with quote

Thanks Eric - Looks like our cars are similar color/type. I will spend some "quality time" under the car to check the ground as you suggested. Also will have the alternator checked by autozone.

I'll be taking it off the road for winter, but I want to have a plan for spring. I owe it some TLC - I've driven it for 17 years and its likes to run. The 924's been pissed ever since I brought home a BMW Z3 roadster and I must make amends. I like the 924 more - it takes tight corners with less fuss.

And this forum is simply the best.

Any more suggestions on replacement alternators?
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jacobroufa  



Joined: 18 Nov 2016
Posts: 60
Location: Rockford, IL

PostPosted: Thu Oct 26, 2017 12:32 pm    Post subject: Reply with quote

If your current alternator benches good, your belt tension is a likely suspect. When I picked up my '81 last year, I had to replace the rubber bushings and the belt in order to get proper tension enough so that it would charge. With so many miles, it's likely that your bushings are squished to garbage and don't allow the system to keep enough tension.
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pmcaya2  



Joined: 24 Nov 2005
Posts: 181
Location: Scio, NY USA

PostPosted: Thu Oct 26, 2017 3:23 pm    Post subject: Reply with quote

Thanks Jaco - I replaced the belt this summer and tension seems good As you and Eric suggested, I'll replace the bushings. Thanks. Peter
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Eric P  



Joined: 21 Jun 2017
Posts: 94
Location: NY, USA

PostPosted: Fri Oct 27, 2017 2:06 am    Post subject: Reply with quote

pmcaya2 wrote:
Thanks Eric - Looks like our cars are similar color/type. I will spend some "quality time" under the car to check the ground as you suggested. Also will have the alternator checked by autozone.


You can easily rule out a bad ground strap by running a nice thick wire from the alternator housing to the engine block. If that's the issue, your alternator should start charging. When I did mine, the engine damper bracket had snapped and taken the ground strap with it. I didn't find the broken ground wire until I already had the alternator off... and for $65, I assumed I was better off replacing the alternator while I had the old one off. There's nothing worse than installing old parts only to find out that they're junk. That bolt at the top of the alternator was a pain to get a nut onto from the back side. I didn't want to do it twice if I didn't have to.

I still have my old alternator. One of these days I'll bench test it. It may still be good. If not, I believe they're fairly easy to rebuild with new brushes.
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1980 924 NA, US model
1987 924S, US model
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