PeachParts Mercedes-Benz Forum - Odomoter works only part time

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Quote:

Originally Posted by cornemuse (Post 3630675)

I thought I was 'all taken care of' with the repaired odo.
Filled up with the deez' & checked the mpg.
Numbers show about 10% lower mpg since the fix.
The speedo seems to be about 10% off also. <- I know I am going faster than the speedo says, same driving speed but fewer cars passing me!

The replacement odo part was marked as "123 *****" but I have had it sitting around for a few years, dont know if it was out of 240 or 300, auto or manual. Dont know diff ratio.
How is speedo/odo compensated for (gear ratios), a gear in the trans or in the odo unit?

Everything works, just 'off', , ,

-c-

(not pulling it to check #'s) (not yet)

Get the right gears. You'll have to count the teeth on the existing gear and order according to that. The following is the cheapest I've found and these guy have an excellent product.

Product Listing compound gear

Which gear on the odo unit?? Is this a gear I can swap from the old odo unit?

When the speed pointer is removed you lift the pointer anticlockwise over the end stop and then mark its resting place on the dial ,so you fit it back in the right place , or the speed will be out . Also you have afuse in the back of the speedo .It will have a coloured holder, thats not the same as all the others...My gear that had come loose on my speedo was the pot gear, its like a double type in green.

I have been tinkering with the 'bad' replaced odo unit. The shaft with the brass gear on the end slides easily out, (not all the way out yet) & when past the plastic gear, turns easily.

At this point the 'pot metal' gear which is where the problem is, will not turn.
To the point of breaking off a tooth, I think, before turning. (I have not, yet)

Shouldnt it turn easily?? Is there something else that hangs up in there??

I checked the #'s, the one I used to replaced is/was from a 240d. (my car is 300cd)

Where is the gear ratio difference in these two odo units?? The plastic gears? Swappable?

-c-

Since the pot metal gear is worn out and the shaft comes out easily...The pot metal gear should spin relatively easily (assuming the shaft is in place)(i.e by poking it with a paper-clip).

Here is a video demonstrating this behavior:
https://www.youtube.com/watch?v=wFka_Oi1P7g

If it is not spinning freely than either:
1) The intermediate gear (between it and the tripometer) is jammed up
2) The tripometer gears are jammed up somehow.

Best guess.

I believe the gear ratio difference would rely on the rear differential being different between the two cars. That would explain your differences in MPG.

1977–1983, 240D, OM616.912, 3.69, 1.1 Liter
1977–1985, 300D, OM617.912, 3.46, 1.1 Liter

Quote:

Originally Posted by cornemuse (Post 3613150)

Well, yesterday I finally removed the inst panel, thought I was gonna break something removing the steering wheel mounting screw. The whole 'bezel' on the panel came off while removing the panel, for starters. Took the tach & gauges units out & put them in the older panel, as its bezel was intact. Last screw I installed was to a broken off post in the panel body. Superglued the bezel back to orig panel. Put everything back in orig. Now, I have not moved more than 2-3 feet since starting. Lost one of the (8) mounting screws holding gauges in. Cleared bench, not. Swept floor, not. Magnet everywhere, not.
Found a sheet metal screw same (+-) size to replace it. Plus washer. (2 screws have funky washers, lost one of them 'natch). Moved the 'bad' panel out of the way, rattle, oh there it is/was! All back together.

In the car, I thought: I wonder if the speedo cable is the problem? Jacked up one rear tire & started motor. Thought: no inst panel. Thought NO OIL PRESSURE GAUGE CONNECTED!! Thought: OH ****. Turned off key. Realized cars vacuum has bled off. Thought: OH ****!
Here comes the oil. On my legs, on steering column, on carpet. Thought OH ****ing ****!
Held my thumb over oil line. Built up enough vacuum to finally shut off engine. Cleaned up mess. Cleaned up myself. Installed panel. Everything works.

This morning I went to the gym, well not everything works after all, panel/inst lites do not work, none of 'em.

Also, I sat on my vintage 'RayBan' new prescription sunglasses & broke off both temples, biggest bummer of all.

I'm gonna be driving my Blazer for a while, , , , ,

(Oh, yes, got the steering wheel couple 'uh grooves off, , ,)

Things have been going so well, till yesterday.)

-c-

When my odometer failed, I took it to an indy, who had a guy come who replaced it in about an hour for $200. Guy had a satchel full of them. Problem was the guy's replacement needle was a lighter shade than the original. Sigh.

Fortunately I have service records to verify a close estimate of miles between a prior service, the date of the change and a subsequent service. This will show no more than a few hundred mils being "lost" .

Agree with the comment about not pushing the trip reset while the car is moving. Not a good idea:o

Thats the reason they fail . Setting the trip on the move, is a no no .So readers check this out ..And for repairing the oddo , you lift the pointer anticlockwise over the end stop , and mark the dial ,So on fitting the pointer you put it back in the same place .But failing to do this , then the speed will be out .

Quote:

Originally Posted by BWhitmore (Post 3630683)

There are at least two different 125 mph speedometers for a w123 300D. The difference is in the speedometer head, not the transmission. The speedometer for a 1985 model 300D, CD or TD ends in the number 57.

I found an inst cluster from a '82 300d turbo junker auto trans with speedo #123 542 85 01.

Before I R&R the speedo, does anyone know if this has the right gearing for my '83 300cd turbo auto trans automobile??

-c-

The speedometer from a 1982 and a 1983 W123 cars are different. Later today I will post the correct part number for both. The part number for the 1983 300D, CD, TD speedometer is 123 542 18 57.

Then you never read the post i left you about Diselgiant did you.If you had the speedo would read the right speed .You lift the needle over the stop anticlock wise and mark the face plate with a pencil ,before removing it ..On re fitting you put the needle on to the pencil mark and then push needle on , and lift it clock wise over the end stop .If you have no dash lights try the smal knob that sticks out from the front of the speedo face it adjusts the back lighting to dash . The potentiomiter should have been cleaned inside when you had the speedo head out .

This is the potentiomiter you need to look at if no lights are showing on the dash board. [Blue arrow ] if it is not working after you try it .Dont adjust it on the move .

Well, speedo been working ok now, but, speedo works, odo works, on sunday I noticed after starting a trip the (resettable) trip counter was not turning. Stuck at 000.9 mi. Didnt re-set it while driving, after 50 mi. (stopped, car in neutral), reset it. Works fine now.

(fwiw, prior to this issue, for 16 years, I almost allus reset the trip counter after pulling away from the pump. I have been pretty religious about resetting it, 'not moving, in park')

Thought I'd pass this along, thoughts??

-c-

Probably just a gummy reset lever that didn't fully disengage. I reset my ODO when moving all the time.