Speedometer Needle Won't Move When Driving - PeachParts Mercedes-Benz Forum

Squabble · #1 06-30-2014, 08:07 PM

hey all, i've been working on this issue here: Odometer Re-Set

today i got my new used odometer (correct for my car) painted, repaired, and cleaned, and at the corrected miles showing for my car/engine. woo.

after putting everything back together, i've found that everything works correctly except for the speedometer. the needle won't budge. it works fine on the bench when i use a square bit in my drill. it will spin freely and max out at about 55 mph or so. no issues whatsoever. but again, when it goes into the car and everything is installed correctly, no dice. won't move. won't spin, won't read the speed. the trip meter works, the odometer works, all good on that front. it's just the needle and only when installed.

the only difference i noticed between speedometers (besides just having different mph configurations) is that the new one i've installed has a brown VDO plug on the back with two prongs. the one that was in the car had that removed. the hole for that plug was just taped over and it seems the original cable was taped up as well and stuffed back in the dash, meaning i could hook it back up if i need to. do i? what is it?

other than that, all is the same. all good on all other fronts. my speedo cable is square, the square bit spins the dial, the parts are identical outside of the brown plug screwed into the back of the housing.

anyone have any ideas?

DeliveryValve · #2 07-01-2014, 02:40 PM

Quote:

Originally Posted by Squabble

... it works fine on the bench when i use a square bit in my drill. it will spin freely and max out at about 55 mph or so. no issues whatsoever. but again, when it goes into the car and everything is installed correctly, no dice. won't move. won't spin, won't read the speed. the trip meter works, the odometer works, all good on that front. it's just the needle and only when installed.

....
other than that, all is the same. all good on all other fronts. my speedo cable is square, the square bit spins the dial, the parts are identical outside of the brown plug screwed into the back of the housing.

anyone have any ideas?

If your odometer and trip works, then it's most likely not the cable. There is a magnetic wheel that turns the basket for the needle. The question I have is did you remove that part of the assembly? It will include the wheel and speedo cable input connection. If so, are you sure that it is properly in place? I would pull it apart and double check. Also check to see if the basket turns the needle to make sure everything is intact.

Other thing to check is maybe there is sporadic movement on the odometer and trip that you cannot detect without comparing with a gps. Double check to make sure the input connection is not torn up. I think these are made of plastic and there is possibility the cable end is slipping inside it.

Here is a thread for reference.

Backyard speedometer adjustment

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HuskyMan · #3 07-01-2014, 03:35 PM

I had this problem and tried several solutions before finally purchasing two spare instrument panels that were in good condition. One of them works well and it became my defacto instrument panel, speedo now works GREAT. Before, it jerked heavily. I think these VDO panels may be "problem children".

BWhitmore · #4 07-01-2014, 03:49 PM

Try to loosen the speedo cable nut where it attaches to the back of the speedometer head. Also, is the needle sticking to the rest pin because the needle paint was not completely dry? Finally if this does not work you can try to shorten the metal speedo cable about 1/8 inch using a Dremel tool. Be careful not to let the metal cable unravel. Speedo cables stretch over time. Had the exact same problem on my W123. All of these recommendations were given to me by Palo Alto Speedometer.

HuskyMan · #5 07-01-2014, 03:52 PM

Quote:

Originally Posted by BWhitmore

Try to loosen the speedo cable nut where it attaches to the back of the speedometer head. Also, is the needle sticking to the rest pin because the needle paint was not completely dry? Finally if this does not work you can try to shorten the metal speedo cable about 1/8 inch using a Dremel tool. Be careful not to let the metal cable unravel. Speedo cables stretch over time. Had the exact same problem on my W123. All of these recommendations were given to me by Palo Alto Speedometer.

Just curious, when you say shorten the metal speedo cable about 1/8 inch using a Dremel tool, do you mean cutting only the internal rotating square shaped cable 1/8" from the end that connects to the instrument panel?

BWhitmore · #6 07-01-2014, 05:33 PM

Yes, cut the internal metal square cable. Try to back off the nut attaching the cable to the back of the speedo head first. If that works and the nut keeps tightening up by itself that means the metal cable has stretched.

Squabble · #7 07-01-2014, 09:53 PM

excellent suggestions, thanks everyone!

the situation has changed a bit. the needle is now moving freely when i am driving. it isn't shaky at all and using GPS, i'm finding it's dead on accurate.

the problem is starting from a stop. no matter where or what, from my driveway to a stop sign, if i come to a complete stop, the needle won't budge as soon as i'm moving again. i literally have to hit the top of the dash like the Fonz to get it to start responding again. everything goes smoothly, i come to a stop sign, and there it is again, a needle that won't budge. slap the dash and she gets freed up again.

i never removed anything from the speedo assembly when correcting my mileage. it runs like a champ after becoming "unstuck." the needles were freshly painted and might cause some sticking, but it didn't stick while on the bench being tested with a drill.

i'm curious about loosening the nut that holds the cable in. why would that help? (mostly curious because that's the easiest fix...) i know i probably over-tighten almost everything i can back there to avoid potential behind the cluster issues, and probably really cranked it down.