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Alternator: Difference between AC Delco 25888970 & 25888971?
Hello,
Are there differences between AC Delco 25888970 & 25888971? My 2008 6.2L, MN6, Z51 (if that makes a difference) came with a 25888971, but all I can find are 25888970. Both seem to have the same mounting locations, connectors, and clocking of connectors. The labels both read 14V and 145A. Can a 25888970 be used as a replacement for 25888971?
Thanks Dano. I did see that write up of yours as well as your posts in several threads regarding alternators. In fact, I followed your troubleshooting tips in one of the other threads. Thank you for the detailed posts!!
Does anyone know if the 25888970 is for automatic cars only? That is what I am being told, but fail to see how that would make a difference in this case.
That is a pretty good size alternator for a sports car.
I suppose that with all the electronics nowadays it should not be as surprise.
90 amps used to be big.
Someone will have an answer.
90 amps was big. My '74 Trans Am has the on-glass rear window defogger which added the "big" alternator...80 amps. The standard alternator on Firebirds at that time was 55 amps. The alternator models were 10SI and 12SI.
Does anyone know if the 25888970 is for automatic cars only? That is what I am being told, but fail to see how that would make a difference in this case.
Thanks
Not sure about the part numbers you posted as I'm traveling now, but automatic cars have a decoupler on the alternator.
Are there differences between AC Delco 25888970 & 25888971? My 2008 6.2L, MN6, Z51 (if that makes a difference) came with a 25888971, but all I can find are 25888970. Both seem to have the same mounting locations, connectors, and clocking of connectors. The labels both read 14V and 145A. Can a 25888970 be used as a replacement for 25888971?
Thank you
GM (25888970) has a Decoupler (slip clutch type pulley), the GM (25888971) has a standard pulley. My '13 Z06 came with the 8971, and all I could find for replacement was the 8970. So I Swap my original pulley to my replacement alternator. It requires a special tool inserted behind the plastic cover on the front of the pulley (I went to a alternator/starter shop). You can buy the standard pulley and change it over to the 8971 type alternator.
Last edited by VetteFan0613; 03-11-2023 at 02:12 PM.
Because of the higher inertia in the alternator at WOT shifting with an automatic GM uses Overruninng Alternator Decoupling (OAD) pulley. It wouldn't hurt using the OAD with manual. Probably why it's hard to find a non OAD replacement. Not using an OAD with an Automatic might reduce the longevity of ones alternator components, ie the alternator itself, belt and tensioner. They are other manufactures using the same principle, Audi and VW to name a few.
Either alternator will work just fine. Stop overthinking this stuff. If you need higher output buy this:
MECHMAN Made in USA. Not Mexixo or China.. High Output....around $600....and it's shiney. LOL
25888970 has a clutch decoupler built into the alternator's pulley (used in cars with the automatic trans)
25888971 has no decoupler built in the pulley (used in manual trans cars)
Personally, I am betting that you could use either one, no matter what transmission you have ... maybe I'm wrong ?
I believe you're right. In fact I'm using the decoupler pulley off the old alternator you sent me on my m6 car right now. Just to see what happens. So far everything works as it should and the belt is still on. Can't tell any difference.
Can't remember if you told me or not .. Did you ever get that alternator I sent you to work? I believe that we figured out that it had a bad diode in it which caused the overvoltage problem.
and it seemed to work OK. Voltage stayed between mid 13's and mid 14's depending on load, rpm, heat. The diodes actually checked out good and I never found anything obviously wrong when it was apart so I can't say exactly why the overvoltage was happening. I ran it on my car for about a week and then replaced it with a polished alternator I bought, keeping the decoupler pulley.
So yes, I got it to work, but I'm not 100% sure it's fixed for good because I didn't use it for very long.
25888970 has a clutch decoupler built into the alternator's pulley (used in cars with the automatic trans)
25888971 has no decoupler built in the pulley (used in manual trans cars)
Personally, I am betting that you could use either one, no matter what transmission you have ... maybe I'm wrong ?
Last Saturday my belt got chucked while cruising. 2012 GS M6. Opened the hood and found the alternator pulley retainer nut had walked backward and loosened the pulley to where it was just dangling and free spinning on the shaft.
It's the original alternator 25888971. I called a GM dealership, asked about the alternator - gave them my VIN number, the system only showed the 25888970 unit for my car. The parts clerk said the previous part number was 25888971. I cross checked this my Corvette mechanic. I'm installing the 25888970.
07-05-2015, 11:47 PM
Alternator: Difference between AC Delco 25888970 & 25888971?
Dano, thanks for this writeup, this is what I will do if and when my alternator starts acting up. 
