Alternator upgrade for a 123
 

I posted this on a an old thread at
http://www.peachparts.com/shopforum/car-audio-multimedia/53236-installed-143a-alternator-my-w124-86-95e-class-photos.html?highlight=Alternator+upgrade

I know I'll get a faster response here. Any reason not to put a 137 amp alternator from a 1984 500SEL into a 1984 300D-T? (yes, I know Jimmy is watching) From the other thread, looks like all I need is some larger connecting wires.

I don't see why not. I have an alternator from a 420SEL in my 300D.

I have an 80Amp from a Saab in mine. :D And I have a 115A unit from a Saab ready in my inventory should either of them fail on either car.....

why?
 

Any reason not to put a 137 amp alternator

1 no reason to
2 waste of time
3 don't need it

i used to have a 55amp on my semi's and it powered everything fine. only thing it will do is re-charge the battery faster. maybe.

1. Mine has a bad mounting hole
2. It would take more time to swap out parts that to put the bigger one in.
3. Not much highway driving anymore. A lot of short trips and starts so I assume keeping the battery charged better will make it last longer.

Reason's 1 and 2 sound good by me.

Pelon, the 55A alternator on a semi also charges at 24V. Those amps are flowing at a higher voltage than 55A @ 12V. It's significantly different.
If you understand Ohms law then this should make sense.

If you plan on adding an amp or other electricity eaters, it's not a bad idea to upgrade. I have a 70 amp that is a direct drop in from an 82 gasoline S class.

On mine the 80A helps a lot in the winter where there is lots of idling in slow traffic with the defroster glass, blower, headlights, wipers, etc...all on. It now maintains voltage above 13V at idle with all that on, it used to dip well below 12V with the 65A unit.

I also have the afterglow glowplugs, which draw about 55 amps for a few minutes after starting the car....

good to know that early w126 81-85 alternators fit into late model w123's. i'll keep that in mind in case i put a killer system in my 300dt

I just put on a 120 AMP alternator last weekend. I was having charging problems. My 55 amp alternator had some internal damage. I figured for just a little more, I could upgrade. I bought mine off of E-Bay from Eaglealternators or something like that. I did read a few previous threads on the subject. The one was for W124's though. It showed two 4 ga. wires. On my 240d, I needed only one 4 ga,about 18 inches in length, wire from the alternator to the starter. This replaced the two 10 ga wires. I reused the blue signal wire. There are two other wires of about 8 to 10 ga. that attach to the starter with the two original 10ga alternator. I used a 4 ga battery wire terminal for those two. I used a 6ga terminal on both ends of the 4 ga wire. I replaced the battery cable with a 2 ft in length 1 gage from NAPA. I soldiered the wired into the connectors. I did then crimp some of them too. I used heat shrink tubing to cover the connectors. I also put some on the two 10ga or 8 ga wires that go to the glow plug relay and the light switch.
I did have a problem that I couldn't get the original 'V' belt (m13 1025) to go over the pulley. With that belt the alternator would contact the by-pass tube on the water pump. I used a M13 1050 'V' belt.
Tom

what car do you have a M13 belt on?
the 240? really? I'll have to look at mine, I never noticed that.
I thought the belts were 10mm Hmmm

I have an '91 240D with manual transmission. I did look at Fastlanes listing of belts for it. It looks like there are different widths and lengths of belts, depending on VIN number and auto vs manual. I saw 10MM, 12.5 MM and 13MM.
Tom

Before going overboard with amp upgrades, you should know how much amperage you really need and upgrade to that much only. The higher the amperage output, the greater the drag on the engine - fewer MPG.

Putting a bigger amperage alternator in the car will not affect the MPG per se. It only affects MPG when you are drawing a lot of current to power whatever you need to power.

I concur with members here that unless you need the extra current/power or your alternator has gone south then it is not necessary to do the upgrade.

What ah-kay said. It only puts extra drag on the engine if it is generating extra amperage - and it only generates extra amperage if you need it (fuel line heaters, big stereo, other heavy electrical loads).

I can see doing an upgrade to 80 amps or so for heavier winter current loads while running low RPMs. But I can't see needing more than that unless you have one of those stereos that rattle the windows or an electric suprcharger or something...