Stuck / Broken W124 Tachometer - How to fix?

[IMD]

Hi all,

Just when I thought I was making some progress in getting the car sorted, another problem crops up!

I have a 1990 230e saloon and the tachometer has just stopped working. Both the main mileage tachometer and the small trip mileage clock have stuck this morning and will not move. I pressed in the mileage button earlier today, to see if this would help and the clock went to zero...then it just stuck there. The button presses in ok, but does nothing.

Is there an easy fix for this, maybe a cable having come loose? How would I get the speedo out to look. Any ideas would be helpful.

Thanks

Ian

[Dieselman]

I suspect you mean the odomenter not the tachometer.

IOf the speedo works but not eh odometer it will be the drive gears inside th espeedo head unit. one in particular has a tedency to split so it no longer grips the shaft it drives.

With care it can be taken apart and either a new gear installed or the old one wired and glued together.

[andy_k]

getting the speedo out means you have to remove the dash panel, either using the "official MB tools" which at the end of the day are just bits of hook shaped wire or you push it out from behind

Drop the trim below the steering column, reach up until you find the console and give it a gentle push, it will come out far enough to allow you to disconnect the speedo drive cable, disconnect the multi block connector and then wiggle the pod past your steering wheel - it's tight, but they do come out without removing the wheel

HTH

Before you put it back in, it's worth changing all the little dial illumination bulbs because if you don't you can guarantee one of them will self destruct

Andy

[IMD]

Thanks guys, yes it is the odometer thats not working, together with the trip meter underneath.

I remember that the trip would not press in at all, so I could not reset it. Now it does press in and both dials have stopped turning, with the odometer figures looking a little out of line.

I'll have a look when I get some time!

Cheers

Ian

[stats007]

I have just fixed mine on my W201. The trip odometer has a metal bar that aligns the gears - mine had worked loose.

Getting it out is pretty much as Andy describes - my air vents were out so I had no need to drop the lower trim panel.

Out of interest does anyone know how the damping works on the speed/tachometers?

[Dieselman]

Not sure but it will be either silicon oil damped or uses the magnetic flux created in the spinning disk.

[stats007]

I figure it's coil based looking at it as opposed to mechanical.

[Dieselman]

Is it electric or cable driven. I would've thought cable on a 190?

[stats007]

Cable, though the tachometer is electronic.

[Dieselman]

Sorry, yes the Taco will be as it's just a voltmeter which uses the coil -ve return to create the voltage.

It's fed with 12v one side and the return drags further towards 0v the higher the engine revs (more sparks per second).

Et voilla, the needle moves up. The damping is probably a small silicon pad or chamber.

[stats007]

They both wobble a bit. It's coming back out again at the weekend so will have a better look.

[Dieselman]

Try the taco with the speedo cable disconnected. Maybe the wobble is speedo induced.

[stats007]

I think the field strength is low as it happens when changing gear. Probably just old age and either the magnets have deteriorated or the coil is shorting.

[Frank O' Phile]

Recently fixed the same problem in my 124.

As already stated it is (probably) due to a gear wheel not gripping on the rotating spindle.

Not a really complex job, but a bit fiddly and patience is a virtue.

The main stages are:-

• Remove instrument cluster. disconnect everything from the back. (steering wheel stays in place)
• Remove screws holding speedo unit (including one for light dimmer resistor and pull it off).
• The speedo unit can be taken out of the cluster but can be a bit awkward.
• Gently lift the needle over the stop pin and mark (or photograph its natural position). then pull it off and you may need some force.
• remove 2 screws holding speedo face and place aside.
• Looking from the side you will see the spindle that runs through the mileage numbers. the shaft can be pulled out just enough to release the gear\drive wheel on the r\h\s which can then be lifted out (I used tweezers here).
• I then applied a drop and bearing locking \sealant stuff (you know what I mean, like threadlock) onto the visible part of the spindle and reassemble.
• A little dab of glue on the speedo needle to keep the black centre in place and you should be done.
• Three days later, pull out the cluster once more to reconnect the vacuum line to ecomony gauge and hey presto the sucking noise goes away.

Give it a go and let us know how you get on. send me PM if you need any further details.

p.s. my speedo is more accurate now, showing only 2 mph slow at 70

[IMD]

Thanks for the advice guys. I'll leave it to the weekend and give myself a couple of days to play around.

I'm in no rush, as it means the mileage stays low! (but the honest part of me wants to get it done soon!)

I'll let you know what happens and maybe take some pics to upload of the process.

Cheers

Ian