I am looking at '85 W123 which is in a really good shape. However the odometer is set at 300K. I've asked the dealer and he told me that they have prior service records that indicate lower mileage around 100K and that it is possible that cluster was replaced and that the odometer reading was carried from that donor. Is that a possibility?

Yes, the gears in odometers of those years get brittle with age. I've seen them stop working due to broken gears with as little as 87K on them. I have an 85 380SE with just that issue.

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84 300SD
85 380SE
83 528e
95 318ic

True enough that the gears often are a problem. But they're easily replaced, and the numbers can easily be reset to maintain continuity. Since it's a VIN car, pull the Carfax and check the history.

I'd like to add a few K to mine. The odo was not working for about five years. I changed it to a odo which had less than the original then replace the gears in the original and put it back on the cluster.

I know this situation is a fluster cluck but adding 20-25K on the one I have now would get it real close to accurate.

No one has touched the car but me and I've not kept the best records on oil changes and filters because I have no intention of selling it.

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84 300SD
85 380SE
83 528e
95 318ic

My w123 82 240d had the full mechanical odometer drive. It had the classic slipping on the shaft issue. I recall it was easy to add on the miles the PO told me about (about 25,000). I just separated the number wheels and advanced the digits...kind of like rollback but forward instead.

My w126 300sd has another issue. When I go faster than say 55mph it doesn't click off miles reliably. It advances, but it seems to skip beats. I've verified this on my GPS. I've heard these electromechanical units have rotting gears. But mine seems to work at slow speed. I can hear a click.

One day I'll open it up. For now I get all upset when I calculate mpg and get some awful number like 18 mpg because the odometer didn't click off my 65mph road trip on the highway.

Did the 85 w123 go to an electronic pickup like my SD?

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

On these cars, I would say the odometer is always suspect unless it can be backed by service records. It could have freezed up and then be fixed later, but later could be 10,000 or 100,000 miles later. It could have also been swapped with a working speedo of lower or higher miles.

Dkr.

Carfax is a good idea to get an idea of mileage. Although, sometimes they don't capture all mileage points if it doesn't get emissions tested or dealer serviced.

As far as finding clues if the speedo is original to the car, What's the part number of the speedo in face plate. An '85 300d has a specific part number and often a replacement is not correct. Also, you can pull the cluster out and see the month and year date stamps on each gauge component. The month should be close to the build date on your driver's side door jamb vin plate.


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1983 123.133 California
- GreaseCar Veg System

Hey, I fixed my slipping odometer today. Rotten gears. Easy fix. Replaced with garagistic set.

I was missing teeth on the little pinion and some on one of the bigger gears. The funny thing is it only quit at high speeds. Well, it works now.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Tip is this .Never zero the trip on the speedo when your on the move.This is what strips out the pot gears and drives gears .. You can replace them ,,and all information is on DISEL GIANT web site Do a Google on it . I think there could be information on this site at the top. HOW TO ARTICALS I have repared a few speedos ,and the ones i have done the problem was the pot gear slipping on the shaft . Main thing is to tape up the tumblers to keep them all together .And to make sure nothing moves out of place .One vital thing is to lift the speed pointer over the end stop and mark the dial with a pencil in the place it rests .Then when you put it back on the speed should be right Any help needed,, pm me i may be able to help you. Thats if you do it yourself

Or, just expose enough of the shaft so you can clamp down on it with a needle-nosed vice grip to create some teeth. The deformed shaft will grip the pot metal gear and not let it slip.

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1982 300CD Petrol/Black Leather

I'm stunned that the car cannot take resetting while in motion. I've heard this before on w123 cars. I would hope there is some kind of slip clutch in the mechanism like there is in a clock or watch that needs to be set while the gear train is in motion.

It is supposed to have some kind of clutching mechanism inside so that the gear train is disconnected from the drive motor. But I cannot say I verified this on my w126 when I was in there last night.

My take is the reset linkage doesn't even move the gears that broke. The gears that broke are a reduction transmission at the speedo input that takes a fast moving motor motion on a tiny 12T pinion and reduces it down to slow motion to move the number wheels. Resetting the number wheels is done with the button linkage way downstream (in the slow motion section). As I said, a sensible design would put a clutch in there.

The reduction is so great between the spinning pinion and the mileage number wheels one could never spin the drive pinion by spinning the number wheels. Ain't gonna happen. Uhh wait...maybe that's what strips it.

Maybe there is a slip clutch and it gets sticky. But in my case I am very sure the gears were rotten. If I had to guess, the oily lube they used softened the plastic. They disintegrated in my fingers as I removed them. The very motion of the car would have taken them out.

That being said, I will not be resetting my speedo on the fly. I really don't know. This is just my thinking and I could be very wrong.

Edit- ok, I take back some of what I said. I looked at images of pushbutton odometer reset mechanisms and yes there is a clutching mechanism. The .1 mile wheel has to slip with respect to the drive geartrain or it simply won't move. The reduction is so great the gears will effectively "jam" the motion of the number wheels. That being said, if the clutch mechanism has too much friction in it, it will put load on the drive gears if you reset it while in motion. It'll put load on the gears if you reset it standing still for that matter too. But I'm sure motion will make things worse.

If the slip bearing/clutch malfunctions even rolling the digit wheels will make the drive pinion that break rotate in reverse at a high speed. Rolling while doing this will only exacerbate the issue.

The gears are rotten so I bet resetting while driving kicks a cheesy set of gears over the edge. Holding the button down while driving will also lock up the downstream mechanism and may destroy the gears. The way the leverage works, moving the number wheels will literally stall the drive pinion.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Someone once told me you shouldn't move an analog clock's hands backwards.
Hasn't seemed to affect things as far as I can tell.

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1982 300CD Petrol/Black Leather

Turning alarm clocks backwards is the no-no, , ie, past the alarms setting.


Which gears in odo head are different for the various differentials options??

(240 - 300 - etc.) (# 001? - # 057?) They are swappable. Or are the different gears in the transmission??

-c-

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"I applaud your elaborate system of denial"

Hmmm. Not sure about the 240d and 300d differences.

I have a 300sd which has the electromechanical drive. The problem there was rotting gears. The 240d odometer I fixed had the classic pinion spinning on the slippery shaft. I fixed that with a tiny dab of super glue.

When folks swap diffs on their 240ds the speedo is wrong. I take it the solution is to get a 300d speedo...but I dunno haven't done it. The tranny is also different between those. When I bought the gears for my SD odometer I noticed the other options for gas 126 or SL cars which conceivably use similar 722 trannies but prolly with different rear ends. People here can explain the differences

Wow, that was a long "I dunno".

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

The poster may have to dig harder. The 85 300d models only had the 2.88 rear ends I think. That means to have an accurate speedometer the replacement must have come from a 1985 model.

A car thought to have this low of miles should still have the factory oil change booklet in the dash. I would also want to check the Mercedes dealers service information on that car if possible. Many of these cars saw dealer service for quite some time. This information is availableto any dealer I believe.

Not all but a signifigant percentage of these cars where purchased to drive high miles. The diesels being selected for the fuel milage. I have seen pictures of this model with 275k miles still looking very good if well cared for and garaged. Of all the cars out there the odometer readings may be the most inaccurate to trust.

Anyways try to avoid paying a premium for a low milage car if is not one. Paying a little more for one in really good shape is okay at the same time.