Like the title says, the speedometer quit on me on the way to work today. No needle movement, no odometer, no trip odometer. I'm thinking one of three things in order of probability. 1. Broken cable. 2. Broken gear drive in the transmission. 3. Broken speedometer head unit. What do you think?

Now to troubleshoot, here is my plan....disconnect the cable at the transmission and the speedometer, connect an electric drill to one end and spin it. If the other end doesn't turn it is obviously a bad cable. If it does turn, then plug the end back into the speedometer and spin again. If the speedometer still doesn't work I probably have a broken speedometer. If it does work it is most likely the gear drive in the transmission. Again, what do you think? Logical and sound troubleshooting process?

Lastly, if it is the cable, how much of a PITA is it to change? If it is (god forbid) the gear drive in the transmission, how hard is that job?

Thanks for any advice, tips, etc....

Most likely busted cluster

If it's the cable it's a fiddly repair but other than getting the rubber firewall grommet in just so it's not hard .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

You don't need to stick a drill on your speedometer to check if it's working. Just put a wooden matchstick in the square hole where the cable goes and turn it. You'll see the needle jump if it's working and you'll probably also be able to see things working, depending upon what kind of speedo you have.
For the cable/transmission check, you can jack up one of rear tires, block ALL the others, take off the parking brake and rotate the tire that is in the air. Have a helper in the driver's seat watch your cable for spinning. If it spins, you know you have either a problem with the speedo or a problem with how the cable was seated. If it doesn't spin, then the cable os broken or your gear in the transmission is broken/slipped.
Then you lower the car, put on the parking brake and do whatever you need to do to get underneath it.
I have this same problem right now, and I haven't followed any of my own advice other than holding the speedometer in my hand and spinning a little matchstick in the cable mount to see if it is working. Speedo works, now I just need the social unrest to stop along with the rain, and that all has to happen on a day off and I can go check to see if the cable is broken.

Phil Forrest

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1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

You know, looking back, I think I ended up having to replace the speedometer cable in this particular car about 5 years ago. Not 100% sure as I seem to be always working on one car or another, and a lot of wrenches have been turned in the last few years. Anyway, if Saturday is nice, I will be seeing what I can find out.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Ok, Looks like the cable snapped. According to everything I read, the complete cable is supposed to be 1460 MM (or about 57.5 inches) long and not able to be pulled easily out of the cable sheath. I disconnected the cable from the speedometer and was easily able to pull out a length roughly 725 MM long or 28.5 inches long. So....it looks like the damn thing snapped pretty much at the halfway point. New cable on order........

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Sweet! Ya got off easy!

Putting that cable in isn’t too hard, but getting the grommet on the firewall is a total pain

Yeah, well, disconnecting the cable end from the transmission was a bit of a *****......not a lot of room to work in there.....ended up pulling the transmission cross member plate and lowering the transmission a bit to get the needed room.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

There’s enough room in there. Pretty tight though. Gotta get some good tools