W115 speedometer error

[BluEyes]

Tried searching, couldn't find anything.

Car is a '71 220D. The odometer reads just about righ on (2% fast) so I'm sure the tire size and speedometer drive gears are right but the speedometer reads WAY low. With the speedometer reading between 45-50, the car is actually doing 60.
Anyone know of a way to fix this without just replacing the spedometer? It would make it alot easier diving without meeding a note sheet to tell me what speed I'm really doing!

[diametricalbenz]

Mine is off too, I suspect I have a 220D odometer in my car AND I have oversize tires so i have 2 sources of error.

I think a competent shop can fix it. Calibrating the speedometer can't be too expensive since the odo and trip work already.

[BluEyes]

how hard is it to adjust these things myself? I've heard there is a spinning magnent in there, and I assume there is a spring on the speedo needle that it works against? There aren't any special tools needed to get in there I assume?
I'd probably have to make an adjustment with some trial and error, using highway runs against a stopwatch to check the reading, but that would be a load cheaper than a shop...

[Mark DiSilvestro]

Many years ago, I had a '72 220 where the speedometer actually broke! That is - the shaft/magnet that connects to the cable snapped at the worm-gear that drives the odometer. After I got a used speedometer and installed the shaft/magnet part in my original unit, I needed to 're-calibrate'. I was able to pull off the speedometer needle, rotate it the appropriate number of degrees/miles and re-install it.
If you're confident that you can do this, go ahead. Otherwise, there are speedometer repair shops around. I think VDO even has a service center here in the US.

Happy Motoring, Mark

[BluEyes]

I can certainly try that, but I'm not sure it is a linear error. I guess I have been going on the assumption that basically the spring is too strong, or the magnent is too weak, but I am at a loss as to how that could have changed with time.
Well, the speedometer is easy enough to remove, might as well take a look.

[Mark DiSilvestro]

In my case, I salvaged a magnet/shaft from a used speedometer, so I had to 're-calibrate'. (The rest of that used speedometer was damaged, so I couldn't simply swap in the whole unit)
In your case, it's possible that the grease at the speedometer needle's bearing has dried and is causing friction. Before re-calibrating, you might try a drop of ATF at that bearing, if you can get at it.
While you're in there, a drop or two of ATF at the shaft bearing and the upper end of the speedometer cable would be a good idea.

Happy Motoring, Mark

[BluEyes]

Okay, I took the speedo apart down to the magnent. Well, it's stil magnetic, and everything in there looks super-clean.
How did you get the speedo needle off? I tried pulling on it, but it didn't budge, and I really don't want to hurt the spring in.
The needle moves freely, but I will try a drop of ATF as you suggest, the little plastic bushing at the end looks completley dry right now.

[Mark DiSilvestro]

As I recall, I had to pull it straight off with my fingers (no tools), while perhaps rocking or twisting the needle center ever so slightly. Also a good idea to mark the needle's position on the cup before you pull the needle off, so you'll have a reference point to reset the needle.
If the needle has become stuck / corroded onto the shaft, there's always a chance of ruining something while trying to remove it, so proceed very cautiously!

Happy Motoring, Mark