Need to Change and Re-Set my Odometer/Speedometer - PeachParts Mercedes-Benz Forum

Squabble · #1 06-25-2014, 08:54 AM

hey all, i'm in need of some assistance and advice regarding my odometer.

i was recently informed that my euro 280E has the wrong odometer for the year and model. i assume it was lost during it's (very poor) federalization process in 1984. it also reads the incorrect mileage as it was driven briefly in germany with the original KPH speedometer before being imported. i have this mileage written down and intend to correct the mileage showing on my new set up.

i found the correct 120 mph gauge on ebay and now have it in my possession. which leads me to my questions.

what is the easiest and best course of action to get my new gauge in with the corrected mileage? i can either:

A) freshen up and install the new gauge i got from ebay in it's entirety. this would mean i would need to roll back the mileage showing by about 20,000 miles. paint the needles, and pop it in.

B) replace just the faceplate of the gauge that is currently in the car and roll the mileage forward by about 10,000 miles or so.

what are your recommendations? how best to roll mileage forward and/or backward? anyone have a write up about this or know of a link to a procedure for tackling the odometer? can you just pop the needles off and change out the faceplate? is that even an option?

thanks!

300dOwner · #2 06-25-2014, 10:10 AM

Try searching the DIY links

http://www.peachparts.com/shopforum/diy-links-parts-category/188540-instrument-cluster-odometer-speedometer-tachometer-links.html

Likely that if you follow the procedure to fix the odo there will be a point at which you can re-align the numbers. WARNING: Be patient and go slow otherwise your odo numbers will be rolling across the floor!

uberwasser · #3 06-25-2014, 11:30 AM

Here is a guide I wrote on repairing an odometer when it stops turning. Some pictures in it might help you when it comes time to swap the odometers between speedometers.

https://www.ifixit.com/Guide/Repairing+Mercedes+W123+Odometer/25421

When it comes to changing the numbers on the odometer to a desired mileage, it's worth noting that the only things keeping you from turning the numbers by hand to a specific mileage are the small plastic gears that drive each number:

If you can pull the shaft out that holds those gears you should then be able to turn the numbers to your heart's content. Then just tape the numbers together so they do not rotate while you re-insert those gears.

NOTE - I have not performed this myself. This is in theory. You may be pioneering this method if you try it, and pioneers often have things go wrong! Use the above method at your own risk, but please do let us know how it goes if you try it, or if you figure out another method.

vstech · #4 06-25-2014, 12:25 PM

instead of using a drill bit, the trip odo shaft is EXACTLY the same size, and it'll likely fall out while you are fiddling with the odo anyway...

VT220D · #5 06-25-2014, 02:04 PM

You will need to replace the entire gauge. Mercedes speedometers are matched to the differential, tire diameter and engine.

The speedometer has a K value (W= on W115/114) stamped or printed on the back - if it isn't rubbed off. The K value indicates the number of cable revolutions per mile (or km). The odometer gears in the speedometer head are selected for this value. The speedometer itself is calibrated to this value.

Furthermore, the shift markings on the speedometer face must match the engine. Diesel engines will have a lower redline and earlier shift points than gas engines. As an example a 74 240D and a 72 250 both share a 3:69 differential and both speedometers will indicate the correct speed in either car but the shift markings will be incorrect for the engine type.

A friend once brought over a 240D with an 85 mph speedometer. Everything looked normal but the indicated speed was off slightly. What caught my eye were the shift points which were much higher. Turns out the speedometer was from a gas powered car with a 3:58 differential. The difference between 3:58 and the 3:69 in the car wasn't huge so nothing seemed amiss but when I rode with him and he ran it through the gears I thought the engine was going to explode!

If you aren't sure if the one you have is correct you can determine the K value of your speedometer by counting the odometer teeth and determining the ratios in the odometer gear train. Then calculate the number of cable rotations necessary to cover one mile. The number will be somewhere between 1200 and 1500.

The K value needed for your car can be determined by calculating the number of driveshaft revolutions per mile and dividing that number by the speedometer drive gear ratio (2.166). Use an online calculator to determine the circumference of your tire.

The K 1425 value shown in the picture is for a W123 240D with a 3:69 ratio. The calculated K value for the car is 1420 - close enough. Interestingly enough the K value for a W115 240D with a 3:69 ratio is 1390 due to the higher aspect ratio of the earlier car's tires. The calculated K value for that car is 1388. - also close enough.

In short Mercedes speedometers are application specific and any mix and match is fraught with peril.

Squabble · #6 06-25-2014, 06:02 PM

Quote:

Originally Posted by VT220D

A friend once brought over a 240D with an 85 mph speedometer. Everything looked normal but the indicated speed was off slightly. What caught my eye were the shift points which were much higher. Turns out the speedometer was from a gas powered car with a 3:58 differential. The difference between 3:58 and the 3:69 in the car wasn't huge so nothing seemed amiss but when I rode with him and he ran it through the gears I thought the engine was going to explode!

are you suggesting that the speedometer tells the transmission when to shift? that's what i'm reading. is that how it works?

i purchased the correct part number with the correct speedometer face-plate for a euro imported 280E from 1984. i guess i feel like i'm making a safe assumption that this is the one i want in my car. the k value was obviously on a sticker that fell off though, so no dice there.

though i have upgraded to 16" wheels, i have purchased the correct tire diameter to match as closely as possibly the original set up. i'm comfortable with the very slight change this has produced.

i'm not looking for exacts here in terms of MPH reading on the gauge. i just want the correct parts on my car that are as close to original as possible. but i definitely don't want to mess with the transmission at all...

still, let's say everything matches up correctly as needed for the car. do you have any thoughts on the original question around dialing the mileage back or forward?

VT220D · #7 06-25-2014, 07:23 PM

Changing the speedometer won't have any impact on when your transmission shifts. The little yellow marks on the speedometer face (I, II, III etc.) are there indicate the maximum speed in each gear.

Since you have an automatic they aren't important. They matter much more to a manual transmission user. The friend I referred to in my last post had a manual and shifted way too late because those markings were incorrect for his diesel.

If the speedometer you purchased is the correct part for your car you should have nothing to worry about. The K value and indicated shift points will be correct for your differential and engine. Changing your wheels won't have any significant impact since you maintained the original diameter.

Because you can't just switch faceplates between the two speedometers the only safe thing to do would be to freshen the new one and roll it back 20k. Any mixing of parts between the two will cause problems.

Sorry if I went a little overboard in my last post but I went into a lot of detail because many people (especially eBay sellers) are either unaware of or are indifferent to how very specific Mercedes speedometers are.

This is compounded by a high odometer failure rate that often ends with a game of musical speedometers. Every W123 I've been that far into either had a broken odometer, a correct replacement with a different date code or an incorrect replacement. I know they're out there but I haven't seen a working original.

Squabble · #8 06-25-2014, 08:21 PM

okay cool. that's what i thought. though i did question my sanity there for a minute.... thanks for clarifying.

good, glad to hear what you've had to say, i feel like i'm on the right track.

it's looking like the only way to go is taking those little gray gears off and rolling the numbers 'round. which sounds like delicate and tedious work...