Mercedes-Benz Forum banner

W638 speedometer displaying way too much

4K views 7 replies 4 participants last post by  Pedr0 
#1 ·
Hi,

I recently bought a second-hand 112CDI with some problems (see other threads). All problems are fixed, except for one:

When I drive the car, the speedometer reads about 25-30% too high (displaying around 70km/h when driving 50, and around 150 when driving 120).
The error seems to be linear and not constant (0 is still 0).

Also, when I turn off the car, the needles do some sort of 'calibration', where they dip down for a second, and then go back to zero.

I have tried searching this and other forums, but no luck in finding a similar problem where the speedometer is this far off.

What could be the cause of this?

Thanks,
Robbe
 
#2 ·
I note from other posts that you have repaired the instrument cluster. Did you remove the needles? If so it's possible that it wasn't replaced in the correct position. The gauges are very sensitive. I had this problem when I changed the facia to plasma glow type. It took a couple of goes to put the speedo needle back correctly


Sent from my iPad using Tapatalk
 
#3 ·
Thank you for the reply.

That is correct, I have removed the needles. I would however find this strange, as the needles seem to self-calibrate when the contact is turned off, and they all move back to 0 exactly.

Also, the error is proportional to the speed I am going, which would not be the case if the needle was installed a bit off I think.

I could always try to re-seat the needle in the correct orientation, but I have no idea how to find this position, especially as there is no keyway or something like that on the axle it is pressed on to.
 
#5 · (Edited)
Hi,

Almost everybody makes this mistake when they take needles off various clusters, including me on the first one I ever did :grin ...........

Before you take them off, you should apply power, (ign on), and photo exactly where the needles sit with Cold Engine, and how much Fuel etc etc, then remove, do the work, then plug back into car and switch Ign on / replace needle in exactly the same position :wink

As above, now it will be trial and error, it will help if you have a gps speed (on phone etc), whilst road testing / calibrating :wink

Oh, and note that they don't all work off ABS, some Manual G/Box Vans have a speed sensor on the Gearbox, all Auto's don't, but they have ABS, some Manuals have ABS, some don't etc etc etc

HTH,

Cheers Dave
 
  • Like
Reactions: BigDW
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top