I just spent hours cleaning and repairing the correct speedometer for the 300D. In essence, I built it from parts. It was beautiful. Then I freaking dropped it. The needle peg no longer rotates freely, and upon inspection, it seems that the centering shaft at the backside of the movement actually snapped off. That's one part I can't swap from a donor unit, as I don't have a good one on hand.

Well, I feel like a moron. Folks, if you're gonna drop your speedometer, do it before you spend all night rebuilding it. Okay? It just makes dropping it feel a billion times worse.

Holy crap... Dumb! Argh!

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Wait! I do have a good shaft! Somehow I think a visit to the speedometer shop for a calibration is going to be required when I'm done. There's no way I'll get the spring tension right.

When you pay $250 to have a speedometer repaired, don't complain. It sounds more and more like a bargain after you've spent over six hours inside of one.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Well, I don't know how I did it, but I did. Using an electric motor to operate the speedometer so it that it reads exactly 60 MPH results in the consistent ticking by of a full mile on the odometer and trip odometer in exactly 60 seconds. I wish I knew how the heck I managed to pull that off, since I had the entire thing as far apart as it would go. Not bad, considering for a while I thought I had completely screwed it up. Now it's time to freshen up the needles with some paint!

I never want to see the inside of this thing again. I sure hope it works for a long time.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Oh man, what a missed opportunity for a good DIY. Well, tell us a little about what you did in there.

__________________
Junqueyardjim
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important. C.S. Lewis



1983 Mercedes W123 240D 4 Speed 285,000 on the road with a 617 turbo, beautiful butter yellow, license plate # 83 240D INDIANA

2003 Jaguar Type X, AWD. beautiful, good mileage,
Mom's car, but I won't let her drive it!

I can do that. In a nut shell, I rebuilt the 110 MPH speedometer from my 300D with a whole, functional 100 MPH 240D speedometer, and bits of what I believe were another 240D unit that was in the trunk when I bought the car.

I took pictures, and will provide further details when I post them. I basically learned how to change a 240D speedometer/odometer in to a 300D version. Only two parts are different, and they are both simple to change. It should make replacing bad units much easier for other owners of some W123's in the future when they can't find the exact unit in the salvage yard, but want to keep the gauge matched to the differential ratio for accurate speed and mileage indication.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

As promised, here are some good photos of the insides of a speedometer from a w123, and a simple explanation of how they work with different rear end gear ratios.

I won't go in to details of how to remove the speedometer from the cluster, as that has been covered very well by others in the past. Once you have your speedometer out of the cluster is when the real fun begins...

First, you have to remember that there is a spring inside of the speedometer for tensioning the needle. Ordinarily, the needle rests on peg when the car isn't moving.


Before you can remove the needle, you must carefully lift the tip of the needle up and over the peg.


Once you've moved the needle over the peg, it will come to rest in a neutral position, i.e., no pretension. Mark this position carefully on the very edge of the gauge face. I used a small dab of permanent marker. The needle must be aligned with this spot when you are finished, or it won't be accurate.


To remove the needle, I found that two spoons on either side of the needle work well. A little duct tape on the backside of the spoons will prevent you from marring the gauge face if you need to re-use it. Lift evenly, as you don't want to bend the thin shaft that the needle rotates on.

Also, the silver, or for later years, black decorative cap on the needle is held in place with a small dab of glue, and pops off pretty easily if you catch just the edges of it with the two spoons. One of the gauges I disassembled had been exposed to a lot of moisture, and corroded the needle to the shaft. With the cap popped off, a drop of penetrating fluid over the hole in the center of the needle will wick down the shaft, and make it easier to remove.


With the needle removed, take out the two screws holding the gauge face on. Be careful to use a screwdriver that fits properly. You don't want to booger up these screw heads, as the damage will be readily visible if you do.

A little secret about the gauge faces I have worked with first-hand. All of them are the same face, essentially, but the numerals are in different places. The rest of the speedometer itself is the same, no matter which car it came from. I have verified that the odometer mechanism is essentially identical for 300D's and 240D's as well, with varying gearing providing proper input to the odometer mechanism. The difference is in the gauge face. Where the needle points at 50 MPH on a 240D, it points at 55 MPH on a 300D, and so on. The degrees of movement as well as pretension and zero rest point are the same, and I suspect all W123 cars, and possibly some others use the same design. More on that later.


Details continued in next post...

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

With the gauge face out of the way, we see the odometer/speedometer guts. The two plastic gear shafts that commonly commit suicide are visible. Notice the one with the red arrow pointing to it - This gear will have a different tooth count and pitch, depending on which gear ratio is present in the car it came from. The end that drives the brass gear is where the difference between a 240D and a 300D odometer lies. The brass gear itself is the same for either car, however.

By changing the plastic gear out for one that matches your driveline, the odometer will register mileage correctly. There are no other differences in the odometer itself. Swap this gear and match it up to the proper gauge face, and you can convert a 240D speedometer to a 300D version, and vice versa. Neat, huh?


In order to get to that gear and swap it out, or to do any odometer repairs needed, the next step is to remove these two screws indicated by the red arrows. Be careful pulling the back off once the screws are removed to avoid damaging the tiny spindle that is attached to the speed cup. Lift it straight away without twisting or tilting it.


the plastic gear shaft in question can now safely be removed, and if you're only changing out that part, all that's left to do is a little careful reassembly with the gear, and speedometer face of your choice. By now, I'm sure you're all riveted to your chairs. Err... Actually, most of you with any sense have hopefully stopped reading by now, and decided to just pay someone to do it for you.

One final note before reassembly: When reattaching the back half of the speedometer, you'll see a tiny shaft inside of the speed cup. Don't break it. This thing will snap off if you look at it funny. This speed cup has already lost the shaft that keeps in centered and balanced as it rotates. It's what I broke when I dropped my first rebuilt attempt. The picture is of the speed cup after the needle snapped off, as the photo of the good part turned out too blurry to be useful.


Here is the plastic bushing-thing, (Real technical term, eh? I don't actually know what it's called.) It's the off-white bit in the center. The shaft of the speed cup fits right up in there and does its thing. Without it, the speedometer won't work at all. Be very careful during reassembly that everything lines up perfectly!



If anyone wants further details, I can provide them. I had to remove the speed cup to replace it, since the only good one I had was attached to an odometer that a PO handled like a gorilla suffering from heroin withdrawals. I have pictures of the entire process, but I'm not sure if they'll be of use to anyone else. Speak up if you want to see more!

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

What a nice write-up, with pics. VERY useful info, and a lock for the Wiki page.
Thanks for your efforts!

__________________
Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

"Speak up if you want to see more!"

I always want to see more.

Kudos for sticking with it and fixing it instead of giving up after you dropped it. I really like the 2 spoons as pry bars. I always improvise and utilize what's laying around also.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Yup you are right - I want to pay someone to do this for me.

The question I have from both your great description and DieselGiant's is what you do with those plastic gears. If they are stripped or broken, can you buy new ones?

If I found a speedo/odo at a junkyard that was properly geared could I just swap it out of the cluster? That seems easier that a rebuild, but then I still would need to change the mileage - would that end up costing me the same as having my existing one rebuilt?

I am weiging my options, but I am now pretty convinced that I don't want to disassemble the odometer myself!

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Great job! Thanks for all the great tips!

__________________
1983 123.133 California
- GreaseCar Veg System

good job......gives a sense of accomplishment, doesn't it.
as for me, $250 sounds like a good deal

__________________
81 Mercedes 300SD 289k.......SOLD
82 Mercedes 300CD 252k......slow ride

82 mercedes 300 SD...mi Unknown
83 Mercedes 300D ????ksniff..gone too
84 Mercedes 300D 148k........SOLD
85 Mercedes 300TD 386k and holding some one elses project

Yeah. Those gears are out there. I've found at least one source for them. I lucked out, and had good gears in the 300D speedometer, so I didn't order any. I can't think of the website off the top of my head.

Completely stripping the speedometer down isn't really hard, but it does take a while. Subtract the time I spent on re-doing my work after dropping one, and it took me about three hours to clean and repair one. Add more time and frustration if calibration is needed when you're finished. I'm very mechanically inclined, but I'd say anyone with moderate mechanical skills and a couple of basic tools could handle the job. I'm pretty sure we all have a set of specialty spoons laying around, too.

As for just swapping out a spedometer goes, just find one that'll bolt in, and make sure the gear ratio is correct, and you'll be good to go. That is assuming you find not only the correct unit, but also one that is functioning properly. The speedometer portion is pretty robust, but the odometer part does seem prone to a couple of common failure points based on my research and limited experience with them.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

Okay, you talked me in to it. More to come, including how to bench test calibration, set an odometer to the proper mileage,and restore the appearance of faded needles. Don't you all be usin' my info to roll back the miles, though! And no rolling them forward, either. You all will just have to wait for your mileage badges, and earn them the right way.

__________________
- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work

My '77 300D progress thread

very nice write up