Odometer running way fast - PeachParts Mercedes-Benz Forum

natew · #1 06-02-2014, 12:52 PM

When I bought this car the odo wasn't working. I took it apart and replaced a gear. It has been working fine for 6 months. I just noticed this weekend it is running too fast. It clocked 9.8 miles when my gps said 4.8. What could be causing this? Speedo is working correctly.

I did have a fuel line break and had to drive 90 miles with it spewing fuel on the side of the engine. I don't think there are any sensors that have to do with speed in that area though.

JamesDean · #2 06-02-2014, 01:06 PM

Did you replace the gear with one of the same tooth count?

Perhaps someone replaced other gears in the unit that make it run too fast?

TheDon · #3 06-02-2014, 01:10 PM

Why bother, you'll get those mileage awards even faster now!

mach4 · #4 06-02-2014, 01:10 PM

Quote:

Originally Posted by natew

When I bought this car the odo wasn't working. I took it apart and replaced a gear. It has been working fine for 6 months. I just noticed this weekend it is running too fast. It clocked 9.8 miles when my gps said 4.8. What could be causing this? Speedo is working correctly.

I did have a fuel line break and had to drive 90 miles with it spewing fuel on the side of the engine. I don't think there are any sensors that have to do with speed in that area though.

Fuel has nothing to do with odometer. The speedometer and odometer are completely separate items. They both however take a signal from the transmission and process it to provide the proper output. The fact that the speedometer is reading properly indicates that the signal is fine, so the problem is somewhere in the odometer. Logic would say it's the gears that are the problem since you just replaced the gears. If the odometer were reading low one might suspect gears slipping, but certainly not the other way, so presumably gears are OK. I think the odometer electronics are suspect...maybe bad caps as these are notorious as the cause of problems in the clock, cruise control, EGR and tach. The ratio you're seeing might lead one to believe that the odometer stepper motor is reading two pulses for every one the transmission VR sensor is putting out.

Other than that, I'm at a loss.

I'd be inclined to just go to the junk yard and source a new odometer module.

BTW which car is the one with the problem?

natew · #5 06-02-2014, 01:35 PM

87 300sdl. I know it's not the gears because it has been working properly with the new gear for 6 months. I know it has nothing to do with fuel but was suggesting that the fuel that was leaking down the side of the engine may have got into some electrical component and was shorting it. I do have an odometer from a junkyard but it has about 80,000 more miles than I have now. I will try replacing the caps. Is there an easy way to turn back the miles on the spare odo I have so it aligns with my maintenance records?

mach4 · #6 06-02-2014, 02:26 PM

Quote:

Originally Posted by natew

87 300sdl. I know it's not the gears because it has been working properly with the new gear for 6 months. I know it has nothing to do with fuel but was suggesting that the fuel that was leaking down the side of the engine may have got into some electrical component and was shorting it. I do have an odometer from a junkyard but it has about 80,000 more miles than I have now. I will try replacing the caps. Is there an easy way to turn back the miles on the spare odo I have so it aligns with my maintenance records?

I'm not sure it's "easy" but this thread might give you some generalized guidance. How to Repair Your Broken Odometer Yours will be different, but I think the principle might work.

Quote:

I recommend getting some scotch tape and lay on the numbers so that they don't move.

Very gently remove the pressed on collar that holds the numbers shaft. Actually you can pry it off or just take some needle nose pliers and pull. To reinstall just take your needle nose pliers and slowly push back on. It is not on with great force to begin with. Please make sure when you reinstall that you leave a little room so the shaft does not bind, ie some end play. With the collar on slam tight it will prevent the shaft from turning properly. I got a drill bit the same diameter as the shaft (7/64) to slip in behind, as I was removing the shaft. GO SLOW and CAREFUL. Don't let the drill bit get too far behind the shaft as you are removing, or the gears will get out of phase.

Worth a shot, I think.

ah-kay · #7 07-20-2019, 12:18 PM

Don't expect the OP will be around to add info. I have the same problem. The odo was running fine for years, nothing done to it as far as gears are concerned. It stopped rolling for a day or 2. Suddenly it restarts but it is registering twice or 3 times the miles travelled. Any idea? It is a 300sdl also. Dash module or the electronics in the transmission. Any ideas?