300 SD alternator output - PeachParts Mercedes-Benz Forum

jim messina · #1 08-19-2008, 10:29 AM

Need to swap alternators. Cd manual says 55 amp output is this correct or should I get the 65 amp?

Thanks Jim

Carson357 · #2 08-19-2008, 10:34 AM

if you can get the higher output it is always better, especially with a/c and power windows etc.. nice to have additional if needed.

pawoSD · #3 08-19-2008, 10:35 AM

At least 65A, even that is not good enough. You can swap in the 80A unit thats used on a 380SEC/SEL easy, its a direct swap and will plug into the existing cables. Or you can find an AL129x and go up to 120A, you just have to replace some wiring.

charmalu · #4 08-19-2008, 10:57 AM

As long as you are going to go to all the work to change it, go to the higher out. Go to your favorite Pick N Pull and pull one.

The AL129X alternator is what is used on the SAAB`s. I pulled one that the
PO much have just put on. they are used on the engines that sit sideways. the one I pulled was off an 87. so if you go that route pull the R/F wheel off and the plastic splash shield, and there it is.

Do a search on AL129X.

Think I paid about $20.00

there are tons of w126 gassers and they use the 80 amp. If you go that route then just replace the voltage relay with a new one.

Charlie

LUVMBDiesels · #5 08-19-2008, 12:39 PM

Go with the AL129X it is well worth it. I have a newly rebuilt one that I cannot use any longer I am willing to sell it for what I paid for it...

You simply install it into the same bracket the old alt was in. then you run heavier gauge wire from the post on the fender where the two thicker wires are connected to the original alternator to the big bolt on the 129x and then run a lighter gauge wire from the post on the fender where the thin blue wire is connected to the smaller thinner bolt on the alternator. That's it it is maybe a 45 minute swap and doubles the output of your electrical system. I was able to run my front defroster, rear defroster, headlights, fogs, wipers, radio, and RADAR detector without going into a low voltage situation...

jim messina · #6 08-19-2008, 02:38 PM

I never really wrenched on anything untill I bought this benz. Battery was dead this morning so the first thing I checked was to make sure I left nothing on. Nope,so I put the charger on her for a hour and a half and fired her up and the battery light was on. Checked the belts and they seemed good so I took it to auto zoo to test alternator. (

First mistake) He tells me the alternator is bad, I said are you sure its not the voltage regulator? He tell me its internal to the alternator so I think its inside.They had one in stock at a store 7 miles away. So I go home to price shop and remove the unit for the core. In the meantime I found the conflicting info on the amperage. I called Roy for his opinion and found out that the regulator could be swapped out

and it is almost certainly the problem. Auto zoo just doesn't sell them seperately. I removed the regulator and sure enough the magnets were worn down, one was only a 1/4 inch long got a new one, put it in. Reinstalled the alternator and back on the road.
Could of saved some work by searching the site.

Thanks to Roy I saved over a 100 bucks and am lucky to have him to consule me.A little extra work but I guess end result is all that matters. Thanks for the replys and the offer of parts gentelmen. Roy, lunch is on me!

Jim

pawoSD · #7 08-19-2008, 03:17 PM

Those little things sticking out of the regulator that were worn down are brushes, not magnets. They are simply there to transmit power from a moving source. An alternator is a lot like a brush motor (almost the same), its just working in reverse.

jim messina · #8 08-19-2008, 08:28 PM

Ok brushes Paws,lol. I told you I don't know much.It is kinda fun working on this car and learning a few things.I haven't had a stuck bolt yet all have broken loose with ease, even the starter bolts broke loose easy as pie along with the trans lines to the radiator. I think I can attribute that to her never seeing a winter? This site is much appreciated I couldn't do it without you guys.

Jim

pawoSD · #9 08-19-2008, 08:42 PM

Thats what we're here for.

Always glad to help! Count yourself lucky with the bolts all coming loose nicely.....it really makes a difference when the car has never seen winter....those that have like to cause lots of problems for their owners.

Our project SD we're working on has never seen winter, its amazing to work on one with no rust or stuck bolts! Its nice knowing the next bolt won't be stuck or break off!