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99 Forester Alternator & 98 Forester donor


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6 replies to this topic

#1 hohieu

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Posted 15 November 2011 - 07:14 PM

'99 Forester with 170K miles, original alternator

So I guess I'm in it for the long haul: just replaced the clutch and ball joints and will be doing the struts after the winter.

I'll be doing some long road trips for the holidays and was thinking about taking apart the alternator and perhaps swapping in some parts from a donor low-mileage unit off a '98 forester. They're not interchangeable. The 98' DOHC alt. has a 2 spade rectangular plug while the '99 SOHC alt. has a 3-spade oval plug. I suppose I could also splice in another pigtail to accommodate the '98 alternator.

In any case, the bearings and rotor are easy enough to replace, but some soldering is required to remove and test the regulator and rectifier and to replace the brush. Are there any parts that are more prone to failure? I'd rather not have to disassemble the whole thing.

I'd appreciate your advice and guidance. Thanks.

#2 Fairtax4me

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Posted 15 November 2011 - 11:16 PM

I literally JUST did this last week. Just cut the pigtail off the 98 and stick it on the 99. The wire colors even match, although even if you didn't have the right colors it isn't hard to figure out. Then swap the whole alternator, or go to Subaru and get one of their $75 reman. units if you need some extra peace of mind.

Part number: 23700AA34ARA

If you don;t have the 98 donor car, the plug from any 95 - 99 Legacy will work. Just hook the white wire to the Blue/red one on the Forester, and the black/white goes to the black/white. The black/white is the wire to the battery indicator lamp in the dash. The blue/red wire comes from the fuse panel. SBF3 I think.

Edited by Fairtax4me, 15 November 2011 - 11:21 PM.


#3 hohieu

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Posted 16 November 2011 - 06:57 PM

Thanks for the info., Fairtax. The '98 alternator is a spare that came off of a jdm engine so I don't have an extra pigtail. If I did, I'd probably just stick both in the car as a spare.

Even though the '98 alternator tested just fine, I worry that it may also have the old regulator/brush holder assembly that was problematic. I'm guessing that newer style '99 alternator has an updated regulator and, thus, the different 3-spade plug.

So has anyone on here rebuilt these alternators?

#4 Fairtax4me

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Posted 17 November 2011 - 11:02 PM

98 Forester had a different part number than the Legacy's that had all the trouble. All the parts places I looked listed a different alternator for the Forester, even though it fits the same. Subaru sells it reman for about $400.

#5 hohieu

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Posted 18 November 2011 - 06:52 AM

I knew that the updated alternators were more expensive, but that's incredible, :eek:. I wonder if it's simply a supply issue or whether the updated alternator is that much better. According to the adjacent thread by Ravenwoods, they're still failing. I may just take the old one out and inspect/replace the wear items: bearings, rotor, and brushes.

#6 Fairtax4me

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Posted 18 November 2011 - 12:37 PM

Yeah and the one for 99 lists for $529, and that's for a reman part. Besides aesthetic differences, the only thing I could find vastly different on the 99 alternator was the 3 pin plug. But the harness only uses two of the pins! So what's the friggin point!? :-p

#7 hohieu

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Posted 20 November 2011 - 08:49 AM

I opened them both up, and besides the front casing, bearings, and brushes, they're actually quite different. The IC regulator, rectifier, and winding connections are all different. All the wear items still seemed fine on the '99 alt. so I'll just reassemble and bolt it back into the car. I'll see if I can get a 2-spade pigtail and put the '98 alt. in the spare tire well just in case...

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