Alternator options

[MrGreenJeans]

Hi all!

My 78 is currently has a Bosch alternator that is only putting out 12.4 volts once at running temp, and there’s no way to add the cooling hose. It’s mostly problematic in traffic on a hot day with the ac on.

In looking at different alternator choices the 90 amp Valeo seems to be the oem option. There’s a high output upgrade that’s really expensive. Then theres the 1988 V6 Camaro model that fits and is stronger (130 I think) but requires some slight modification to the wiring as I understand it.

Anyone ever gone the route of the GM unit? Any naysayers?

[dr bob]

Varying reports from the GM conversion efforts. There's also a closer fit with a Ford/Autolite alternator than was original in the Contour and others in that class. All require some modifications, plus some shimming to keep the belt lined up, and some demand mods to the original mounting and tensioner brackets. All are relative hacks, none particularly interesting at least to me.

Early cars came with either Bosch or sometimes P-R alternators. The Bosch is particularly easy to get rebuilt vs. the P-R. If you are in a major market, some sleuthing might find a rebuilder who can handle the job for you for a lot less than a retailer might, um, charge.

----

I was chasing a charging issue on my S4, and was in denial about the alternator as being a possible cause. Charging and system voltage appeared to be fine, but once in a while it would really struggle to crank. I had meters and test leads strung through the car, trying to figure out whey the battery wasn't holding charge. New Bosch alternator finally when I thought I'd exhausted all options, and... same symptom. Group advice suggested that the battery ground strap might be the problem. I'd driven with a meter across that, looking for voltage drop in the ground strap, and that testing said it wasn't the problem. Of course it was. Inside the insulating sleeve, the copper braid was corroded/rotted from charging fumes. I'd plumbed the battery vent outside the box, but apparently it still suffered. I ended up replacing it, and in the process bought a box of 2ga tined-copper marine-grade straps to share. A bit of heat-shrink, a couple charging port conductors in there too, charging problem magically solved. All those straps are installed in cars now, and the vendor (Waytek) no longer sells them last time I looked. Can't be too hard to find.

For your car, I can suggest that you find an appropriate ground strap and add an insulating sleeve so it will work passing out of the battery box. Your car demands a larger battery (Group 49 IIRC) than my S4 with a Group 48/H6, and therefore a different ground strap length. The ground for the engine underneath is also an exposed-copper cable to the frame rail, and certainly deserves a hard look or just replace it.

---

I ended up refreshing my original while I had it out, and swapped it back in soon after so it's all back to the original parts. New is on the spares shelf, should I ever need it, and it will go with the car when it moves on after my stewardship. I was able to easily find brushes and bearings, the only real wear parts in there. Full cleaning, diodes tested, baked to get it all dried out, then reassembled before it went back in. The voltage regulator is the brush holder, making that part way too easy. Had I needed more, like a rewind or maybe slip-rings replaced, I had shopped a local rebuilder near us above Los Angeles at the time. Anyway, it was a relatively easy actual recovery once the community convinced me to look at the right place.

[Petethepug]

If you’re referring to BNR parts for alternator rebuilds in LA, I’ve been using them for decades.

https://www.ebay.com/str/bnrpartsalternatorsandstarters

All the Bosch rebuilds for my ‘90 Corrado were losing bearings every two years. The guy @ BNR verified his rebuilt 90 to 140amp Bosch alternator would work. He offered to find a cherry picked core for me, add SKF bearings, better fan and stated I’d never have another problem.

That was 10-15 years ago. I still have the extra one I purchased because no one else builds them like them.

[MrGreenJeans]

Thanks for all that! This is my first time dealing with an alternator, so I’m searching out best options.

My car charges fine but I have voltage drops when at idle and the car is hot. Lights dim and hvac fan slows, which I’m assuming also happens at the cooling fan. I have a new engine ground from 928intl. Mark did not have a battery ground strap that would work with a 78, so I found one at autozone that fit though I realize might not be the best choice. I still have my old one.

I’m in Charleston, which isn’t small but it’s not a big city either. According to my records the alternator was replaced not long ago by the PO, but it doesn’t seem to be cutting it. Would this still be a case for a rebuild?

[dr bob]

Voltage drop is pretty normal for alternators. For later cars with auto gearboxes, Porsche spec'd a larger drive pulley on the crank, since they generally run at lower RPM's and need the help. Heat is another derate. Have you taken the alternator to be tested? A better local parts vendor can help you pass/fail the alternator itself. Plus the R&R gives you a chance to inspect/clean the cable connections. Do the primary connections at the starter solenoid and the battery posts. Then the jump post and the FOE cable from the alternator and connections.

I've become a connection-cleaning fanatic. I can't point to it actually saving me, but doing it feels good and has kept problems at bay. Except that battery ground strap, which took me a while to diagnose and I didn't really do that -- the community gets the credit. Hence the box of cables for others in the L.A. clinic family. Pay it forward, right?

[Petethepug]

Over a 15 years ago BNR used upgraded components in a stock Bosch housing for my 90 Corrado g60 that was eating alternator bearings every 2 years. They rebuilt with SKF bearings and took the 90a OEM unit to 140. I’m still running that alternator 15 years later. They found a way to up the amps to 200 now in the same shell.

My recommendation would be to do as previously requested of me when ordering. In the comment section on eBay add “Pls use SKF bearings”. They may charge a little more but 15+ years of longevity is worth it. The quick recharge of a depleted battery from storage or a battery on the fritz via 200amp is what’s needed on a classic to get you and the car off the road safely.

IMG_3758.jpeg (506.8 KiB) Viewed 1167 times

[dr bob]

The voltage regulator includes the brushes and holders. The front bearing is pretty generic. I'd shop locally for a name-brand bearing, like SKF, Fafnir, Timken. The rear bearing is really a bushing, and generally needs just cleaning and new grease. If the alternator is charging now, the diode pack is working. A quick look on eBay finds these kits for under $40 with new Bosch or Hella regulator. No name listed for the bearing. Comes with new rear bushing.

If the little slip rings on your current armature, the copper rings that those brushes contact, this repair kit and an hour of cleaning will give you pretty much the same product that bargain rebuilders offer for $hundreds.

Just sayin'...

[Petethepug]

Yea but, we’re Porsche owners. Capital is never an issue.

[blueline]

Yea but, we’re Porsche owners. Capital is never an issue.

[dr bob]

Yeah... The car generates lots of interest too if that helps... The capitol is just a few hours drive west over the mountains from here, if I run low.

I confess that in my frustration over not solving my own erratic charging issue drove me to actually purchase a new Bosch alternator. All my diagnostics said is wasn't the alternator, but I was running out of straws to grasp so click-ding-brown-truck. And..... No Change. Then new wearing parts ordered for the old one, disassemble, clean, test, reassemble with the known-good pieces, generate new properly-patina'd original Porsche factory part number labels to replace the tired original one (serious overkill right?) to go back into the car, and for the new spare for the shelf.

----

As a part of my spare-time retirement consulting gig tinkering with power plant automation software, I end up doing a serious amount of circuit testing and troubleshooting. Techs are sure the problems are software since they are sure their work is perfect. I'm not always so sure. Anyway, theory and practice usually come together easily for me, even in low-voltage DC stuff. The corrosion problem in the battery ground strap eluded me though.

So my advice steps are to clean and check every connection from battery to jump post, and on to at least the 30 buss in the CE panel. I tested my ground straps half a dozen different ways and times, and now just recommend replacing them if they aren't new. If the alternator charges normally at any time, you are searching for what causes it to droop.

You can still buy the OE cooling shroud for the early alternator, as well as the flex duct that feeds it cooling air. The ducts get oil soaked from dripping PS and sometime engine oil cooler hoses. The ducts get broken and then trashed as the tiring front springs allow the asphalt to get closer. 928 International shows them, as does Pelican and other 928 parts suppliers. The regulator in the alternator has temperature compensation built in to protect the battery. But the 928 battery is in the rear, and the alternator needs extra cooling for itself but particularly to fool the temp compensation. In my experience and education, manufactures tend to avoid adding parts that aren't needed. So I'd be looking to restore the cooling shroud and duct, regardless of other issues you might find.


My strategy starts with "Everything worked fine until X happened. " then solve for X.