HOW-TO: W126 Odometer Repair, Clock Capacitor Replace - Page 2 - PeachParts Mercedes-Benz Forum

JamesDean · #1 02-05-2013, 09:17 AM

Hmmm it looks like, MAYBE with some careful work you could get it out without having to remove the needles. Its hard to say, you might be able to get your soldering iron in there at an angle, and a pair of pliers to pull the cap once you've heated up the joints. The new one is probably smaller so it might be easier to put in...

You might even be able to loosen up the gauge face and move it around for some more room.. I'm not sure.

JamesDean · #2 02-05-2013, 03:10 PM

Bill,

If your car is a 126 chassis then the whole system is electronic. The speed signal is electronic rather than mechanical like the 201/123/124 chassis. There is a small motor that runs the gears on the odometer. A bad capacitor can certainly cause no power to go to that little motor. See step 6 of my orignial post. Those caps have to do with powering up all that stuff on the speedometer/odometer.

BDBENZ · #3 02-05-2013, 04:12 PM

Thank you for the explanation and direction to look. Mine is electronic in a 560SL. The speed works perfect. I will try to replace the capacitors and see if I get power to the stator motor. I have suspected the issue has been electrical. The unit is still out the car so this will be worthwhile to try.

Bill

steh-fan · #4 11-08-2013, 04:17 AM

Quote:

Originally Posted by JamesDean

To gain access to the capacitors you must desolder the speedo from the circuit board. There are a few connections to desolder, these are indicated below in the picture:

After you've finished soldering, just re-assembled everything back as it was. Be sure to re-solder the contacts for the speedo unit to the circuit board and you're all set.

Hi,

I was looking for the picture with the solder points, but unfortauntely, I can't find it. It looks like I can't even access the gears without unsoldering. However, I don't know which connections I would have to unsolder.
Thanks for any help!
steh-fan

JamesDean · #5 11-08-2013, 09:40 AM

I'll have to see if I have the picture on my computer somewhere. Looks like it never got posted.

JamesDean · #6 11-08-2013, 12:12 PM

Updated photo album here:

W126 Odometer / Speedometer / Clock Repair - Imgur

TnBob · #7 11-08-2013, 02:48 PM

Not only great pics but a super service you provide to all the members here.

THANKS

steh-fan · #8 11-25-2013, 07:48 PM

Quote:

Originally Posted by TnBob

Not only great pics but a super service you provide to all the members here.

THANKS

I fully agree to that!

I have two quick questions:
1.) What specifications do the capacitors and resistors have (or RadioShack cat #).
2.) I did the capacitor on my watch and it started working again, but it's showing erratic times. I somewhere read a certain resistor needs to be replaced in order to have it showing the right time. Do you by chance know which on that is?

Again, thanks a lot for your help!!!!

JamesDean · #9 11-26-2013, 01:24 AM

Quote:

Originally Posted by steh-fan

I fully agree to that!

I have two quick questions:
1.) What specifications do the capacitors and resistors have (or RadioShack cat #).
2.) I did the capacitor on my watch and it started working again, but it's showing erratic times. I somewhere read a certain resistor needs to be replaced in order to have it showing the right time. Do you by chance know which on that is?

Again, thanks a lot for your help!!!!

The capacitors on the 300SDL's cluster were
220uF/6V
47uF/16V I think.

I replaced them with:
220uF/6.6V
47uF/50V

The resistor was 33 Ohm, which is available at radioshack as that's where I got it. The capacitors are fairly common values so I think RS should have them as well.

Just be sure to open up your speedometer first before buying supplies so you are sure of what you need. The first gen speedometers are different than the second gen. Second gen are what is listed above. First gen I cant recall at the moment.

I've not seen the replacing the resistor comment. I'd have to look at the clock closer and see. As long as you are using the same capacitance on the replacement capacitor I cant see an obvious explanation for the erratic behavior.

steh-fan · #10 11-27-2013, 01:32 AM

Quote:

Originally Posted by JamesDean

The resistor was 33 Ohm, which is available at radioshack as that's where I got it. The capacitors are fairly common values so I think RS should have them as well.

Hi,

very stupid question, but I wanted to double-check before I buy something wrong; I saw that the resistors come in various wattages. Which one would be the best to use? I think RS mainly stocks 1/8, 1/4, and 1/2 Watt resistors.

Thanks a lot for your help!

JamesDean · #11 11-27-2013, 07:19 AM

Not a stupid question at all. I should have specified. The 33 is a 1/2 watt resistor.

JamesDean · #12 11-25-2013, 03:01 PM

Thanks TnBob!

I just had another speedometer in over the weekend. The owner said that the alternator on his SDL failed and sent out a massive voltage spike through the car's electrical system. It took out the speedometer. I didnt quite know what to expect luckily the damage was not very severe. The spike was absorbed by a resistor and capacitor, both of which died.

Some pics!
W126 Speedometer Repair - Imgur

JamesDean · #13 01-02-2014, 03:14 PM

Has the speedometer pod/cluster ever been changed out with a different unit?

The US 300SE was 3.46 gear ratio evidently..

1989-1991, 300 SE, M103.981 3.0L I6, 3.46 1 Liter

If someone swapped in a US speedometer cluster than that would explain your speed difference.

steh-fan · #14 01-02-2014, 03:24 PM

Quote:

Originally Posted by JamesDean

Has the speedometer pod/cluster ever been changed out with a different unit?

The US 300SE was 3.46 gear ratio evidently..

1989-1991, 300 SE, M103.981 3.0L I6, 3.46 1 Liter

If someone swapped in a US speedometer cluster than that would explain your speed difference.

Hi,

the car was brought to the US in 1999 and yes, they federalized it and swopped the speedometers. That's why I mentioned above that I could easily detect the solder points for removing the speedometer since it has been replaced during the federalization process.

However, it was working correctly until last weekend when I swopped the gears and soldered the speedometer to access the gears.

So something most have gone wrong during that process...

Is there a way of adjusting an US speedometer for the different ratio?
Maybe I was soldering something that was inactivated before....?

JamesDean · #15 01-02-2014, 03:30 PM

I dont think the speedometer head would vary from US to EURO. I think the drive circuitry would change based on diff ratio (at least thats how I would have done it) and since you said it was ok before the change we can assume that the head is Ok and correct.

There are only three or four solder points so thats a low probability of fouling up.

I would replace the capacitors and see what that does. Perhaps the new gears added additional drag on the motor causing it to require more torque/current from the capacitors and if they were marginal to begin with the additional load might make them slow down..

Maybe. Just speculating.