'78 SC, alternators interchangeable?

GC 53 · GC 53's Garage

I need an alternator for my '78 SC and found that Porsche used more than one manufacturer that yr.So are they interchangeable, or do you have to stay with the same one you pull off the car?
Thanks.
Sandy

subdewd · subdewd's Garage

I can tell you that the one in my 83 didn't match
with what is listed in the catalog.

304065 · 07-15-2003, 06:21 AM

there are three types: motorola, bosch and valeo.

All three are interchangable. But you must use the same brand voltage regulator as alternator according to the factory manuals. The Bosch are cheaper, even if you have to change the reg, if you are buying new, but for a rebuild, why not just have the existing one rebuilt if you have isolated the fault to the alternator.

MotoSook · 07-15-2003, 06:27 AM

Just buy a new one with an onboard VR. A Valeo is about 300 bucks. I went through my ALT issues recently and in the end, it's best to just get a new ALT with the undated VR situ.

304065 · 07-15-2003, 06:43 AM

I respectfully disagree, the factory didn't go to internally regulated alternators until 1982, and the internal regulator is subjected to tremendous engine heat. I would recommend sticking with the remote mounted voltage regulator, this will also not require rewiring.

Hetmann · 07-15-2003, 06:54 AM

I believe my 78 had an alternator made by Marchal in France. It looks different than the Bosch. Make sure whatever you get will fit your fan housing.

GC 53 · GC 53's Garage

The problem showed up by the indicator lamp remaining on after engine is started and car is being driven. Car had refused to start when wife came out of store.I took the battery out of my 911 and put it in place of the other dead battery, got the car home (about 4 miles at night) Turned the car off, tried to restart it again and nothing.
Put the battery back in my 911 the next morning, it struggled a bit, but started and hasn't been a problem since.I was guessing it might be her alternator as the car has 144,000 on it.
Any input would be appreciated.

jmohn · jmohn's Garage

Get your existing alternator rebuilt, it's the most cost effective solution, and removes the possibility of getting the wrong unit as well as the need for re-wiring.

Jerry M
'78 SC

GC 53 · GC 53's Garage

Jerry,
Any rcommendations on where to send it for rebuild?
Gary C.

targa80 · targa80's Garage

First, I would try a different V/R They are about $60 bucks and if it doesn't fix it you will always have a spare. Next, pull the alternator and have it tested at a good electric repair/rebuild shop. Or if you are handy and have the knowledge of how the alternator charging circuit works in the car then test and rebuild it yourself. The cheapest is to do the rebuild yourself, next would be the repair shop route or a swap with a refurb. The most costly would be to buy a new one. Each would have a different level of hassle and work involved. I would stay away from the upgrade to the internal V/R due to the reasons in previous posts. Also if the V/R goes out in the internal unit you would have to pull the alternator again. In the old system you disconnect a plug and one screw to remove the V/R. Do a search in the archive there is a lot of info on the alternators and some reasons for failure with cheap fixes.

Hetmann · 07-15-2003, 08:38 AM

While I was having my engine rebuilt I did a cleanup of the alternator and fan assembly. I blew compressed air thru the alt and about a pound of dust came out. Maybe all yours needs a good cleaning out and some new brushes to bring it back.

MotoSook · 07-15-2003, 09:59 AM

Upgrading to the onboard VR does not require any rewiring. You snipe one wire and that's pretty much it. And the alternator sits behind the fan, so anytime the motor is running, the cooler air is rushing over it or is "shielding" the alt from the heat. When the engine is turned off, the heat is the worst, but not much worst than what the external VR sees in the engine bay.

I will admit that having an external VR makes it nice to replace a VR should it fail. It's a matter of preference really, so go with your gut. If you rebuild make sure it is done right, so if anything fails next, it'll be the VR.

Instead of buying a new VR to replace my failed VR, I just opted for a new alt and VR....now I know everything is new..I'm warm an fuzzy now.

I would have always wonder when my rebuild unit will give out next.