The following pertains to the W123 300D with the 617.952 engine.

Having just completed this repair (due to failing alternator bearings)
I thought I'd write up a short narrative on this. The upper and lower mount bolts/nuts are 17mm, and the adjustment nut takes a 12mm socket. The nut on the alternator pulley is 22mm.

Note: If you want to remove the upper alternator bracket (for cleaning, etc) you will want to remove the U shaped air intake boot - otherwise you'll have a really tough time getting at the head of the 17mm bolt.

Removing the alternator from the vehicle:
1. disconnect negative battery cable
2. disconnect the alternator from its wire harness (be gentle), you will have to displace the spring clip securing it in place.
3. loosen alternator belt tension adjustment bolt, remove from alternator and bracket ( you will have to play with this a bit to make it clear the water pump pulley and fan blades) At this point the two belts should be loose, but probably still won't come off the pulley
4. Remove the lower alternator mount bolt ( using a socket wrench with a short extension makes this happen more quickly)
5. Remove alternator, bracing it with your free hand as you remove the bolt, otherwise the alternator will fall on you.

Removing 22mm nut holding the pulley on:
1. place the lower mount bolt you just removed back thru the mount hole in the alternator itself. Place an eight inch or so screwdriver thru the one of the spaces in the cooling vanes. Allow the screwdriver to rest against the bolt - this will secure the pulley from turning when you remove the nut on the end.
2. Secure the body of the alternator so that it won't move. Using an impact wrench, remove the nut from the alternator shaft. It may be possible to use a breaker bar to do this, but I haven't tried.
3. Removing the pulley: If your pulley doesn't just slide off - use a rubber mallet to deliver blows to the face of the pulley around its circumference - this will free the pulley from the rust that will have formed after 20+ years. You will have to work the pulley back and forth to get it to come free.
DO NOT LOSE THE KEY THAT POSITIONS THE PULLEY.

4. Remove the pulley, spacer, and cooling vanes from the dead alternator.
5. Place key into new alternator shaft. Place cooling vanes on next, followed by the spacer, and then the pulley.
6. Place split washer on the shaft, followed by the nut.
7. Immobilize pulley ( I simply placed a cloth in my hand and held the pulley edges). Use impact wrench to tighten.
8. Reinstall alternator, placing the lower mount bolt in and hand tightening
9. Reinstall the upper belt tensioning bolt ( be patient, as getting everything to line up and feeding the bolt thru the mount hole in the alternator may take time)
10. Tension the belts to between 25-30 KG of tension- using a Krikit gage helps tremendously. If you don't have a gauge, just tighten the belt until it won't slip on the alternator pulley - don't go overboard - or you'll shorten the life of the bearings.
11. Attach wire harness, attach negative battery cable, check for any extraneous objects under the hood, and then starter up. This repair took me about 2.5 hours from start to finish- It probably could be done in two hours or less by someone who's done this repair before.

Nice write up.

Here's a similar DIY post I wrote last year (slightly different procedure):

1) Remove the fresh air intake tube to the aircleaner. Remove the aircleaner. Remove the aircleaner to turbo U-tube. Consider removing the tube between the top of the radiator and the coolant expansion tank. Be very carful not to lean on the plastic nipple on top of the radiator while removing installing the alternator, its easy to break off.

2) Remove the battery and put on charger overnight.

3) Unplug the alternator (3-prong plug on the back above the voltage regulator). There may be a spring clip holding it on, just pry the spring with a screwdriver and flip it down (it doesn't come off).

4) There are three bolts that hold the alternator on, all are 17 mm. Loosen all three (toward the rear of the car), then back the 13mm adjusting nut all the way out.

The one on the bottom (goes through a flange on the engine), can be cracked with an open end or box end wrench, and removed with a deep socket.

The inboard one on top is tough to reach. The bolt head is toward the rear of the car and the bolt goes through a flange on the engine block and is threaded into a nut welded to the alternator bracket. Crack the bolt with an open end or box end wrench and then back it out with a short socket, one ratchet click at a time.

The outboard one on the top only needs to be loosened with an open end or box end wrench at the nut towards the back of the car. The head of that bolt should have a long threaded stud coming of the side going to the 13mm adjusting nut.

5) Once you've loosened the two 17mm bolts and one nut, you can back the 13mm adjusting nut all the way out and slip the belts off the pulley.

6) Remove the two 17mm bolts holding the alternator bracket (top) and alternator casing (bottom), and the alternator should drop out the bottom of the engine compartment. Watch your head.

Once its out you can swap the bracket and pulley over. I hold the pulley in a gigantic pair of channel locks wrapped in an old t-shirt to undo/intall the 22mm(?) nut.

Install in reverse order. Put pulley and bracket and adjusting bolt/nut on alternator out of car. Install bottom bolt, install top bolt, snug both up (not tight). Slip on belts, snug up outboard top bolt, tighten belts with adjusting nut. Tighten top outboard bolt, tighten top inboard bolt, tighten bottom bolt. Plug alternator in, flip spring clip back into place (if you have one), install the battery, put all the aircleaner parts back on, reconnect the coolant resevoir, reconnect fully charged battery.

I've done this so many times lately I could do it blindfolded.

Is it supposed to be a double pulley for two belts or a single? I have seen pix of both, probably confusing two different models.

__________________
Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

Both my euro 84 300TD and US 85 300TD had/have double pulley and belts.

I bought a used double from a member here and will switch sometime.

__________________
Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

Thanks for this DIY writeup. My alternator just seized up and I need to replace it.

My alternator belts burned up and came off so I will be replacing the belts as well. I see that they sit to the rear of the vacuum pump belt and the power steering pump belt. How much trouble is it to get these other two belts off? I figure I am into a 2.5 hour job with just the alernator. How much more for the belts?

Thanks for any advice.

__________________
85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

You have to loosen the tensioning and retaining bolts on the power steering pump and A/C compressor to obtain enough slack to remove those belts. Not too hard a procedure.

John

__________________
Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI

Thanks John. I'll have the alternator out tonight and hopfully the rest will go smoothly.

__________________
85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

Well on my 85 euro td the alternator pulley is a 24mm instead of 22mm and i have a single belt,i wonder if theres a way to remove the pulley without an impact wrench,ive tried everything and i CAN'T get the pulley out,when i stick a screwdriver in the alternator to hold the pulley in place the fan blades get screwed up and i do not want to mess them up,im pretty much bummed out at this point.

You may want to shop for an electric impact. I don't think they have the oof that an air impact does, but you don't have to get an air compressor. I was given an old kinda crappy one. But I put new brushes in it and for 25 years it just keeps doing what ever I ask of it.
Or just pop by your local tire store with the alt in hand. Most tire stores would be happy to pop it off for you... ' cause you might remember them when you need to buy tires.....

__________________
Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

most box stores sell a 12V tire tool mini impact wrench that should be sufficient to remove the nut.
around $30

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thats true...I need to pick up one of those sometime.

I have generally ended up cutting a chunk out of the nut with a dremel so it comes off easily...new alt's come with a new nut anyways.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I sprayed mine with a dose of PB Blaster before I tried to get the nut off. It is like liquid wrench on steroids. It worked well.

__________________
85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

Guys- first off thanks for the information here. I found it very helpful.

I used to profess that the engine layout on this vehicle all made a lot of sense once you saw it. The location of hese alternator bolts may cause me to change my mind. When you guys say "one-click at a time" for that back bolt, you are not exaggerating.

Well, one project fixed. On to the next one!