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.

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

Well I repaired my odometer. The shaft runing through the center of all the numbered wheels had one of the gears become loose on one end. I slid the shaft out and a like sized drill bit in from the other side to keep everything in line. Once out, I scored the slipping end and reinserted pushing out the drill bit. Had to tap it back into the other gear that was slipping so I assumed a firm connection. Here's where things went bad.

Decided to test my repair with a drill motor. Found a nail that appeared to be the correct size to fit the back of the speedo on the work bench, test fit looked good. Chucked it into the drill and started spinning. Everything worked great as I ran it over a mile. When I stopped and was pulling the nail back out it was somehow stuck? Pulled a little harder and it pulled an inner sleeve out and poped the needle off the front.

So I'm now looking for a speedo for a 190D with the 2.2 liter automatic. I understand the speedo head in the dash is geared to the differential so I need a 2.2 automatic for the speed to be correct.

Stuff happens!

Clock/speedo repair
 

I've pulled the cluster out of my '84 300SD to repair an intermittent clock. I would like a bit of guidance before I get into it.

My clock works sometimes, but it appears that whether it works or not depends on the position of the knob used to adjust the time. I haven't completely disassembled the clock/tach portion of the cluster, so I don't quite know what I need to be looking at. When the clock stops working, and I re-set the time via the knob, if I'm very careful with how I handle the knob, it will work for weeks on end. Could it be that this is just a coincidence and that the capacitors are actually the problem?

Also, my speedometer and odometer appear to both be reading about 10% too fast, but they work very well. The gears are in good shape, but I don't know why they would both read too fast. I bought the car used, and it has a brand-newly rebuilt transmission from Sun Valley Transmissions (mercedesdismantlers.com). I'm using factory-sized tires (195/70R14), so it's not a tire-size issue. I have two other used clusters, and both of those read 10% too fast also. Could it be that the drive/pickup from the transmission is incorrect?

Any help is greatly appreciated.

The knob actually connects to the clock mechanism via a spring loaded rod type thing and sometimes that can get stuck extended. When it is extended it adjusts the clock so if its stuck the clock is held in position and doesnt change. That might be whats happening to you. Take apart the cluster and observe the knob mechanism, you'll see what I'm talking about.

Hrmm that does sound peculiar. Maybe a previous owner changed the differential or something? That, tires or trans are the only things that I can think of that would cause that difference on BOTH clusters.

Okay, so I took apart the cluster and looked at the knob and gear linkage mechanism for the clock. It appears to function properly and disengages the gears to the clock when the knob is released, so it must be a coincidence that it stops working sometimes. My guess is that the capacitors need replacing. Thoughts?



I realize that the differentials are different in '85 versus previous years (mine is an '84). I looked at the date stamps on the back of my two spare clusters, and they are both '85 cluster units. The funny thing is that they read exactly the same (10% fast) as my current cluster, which has date stamps showing '84 as the year. I think my next plan is to check out the differential. What markings/numbers should I be looking for? I know nothing about identifying the different differentials.

I just realized while typing that the previous owner who had the transmission replaced, listed the car for sale as an '85 300SD, but it's actually an '84. Since the transmission company is in California and the previous owner had the new transmission sent to him here in Salt Lake City, is it possible that, if he told the transmission company it was an '85, they could have used different parts specific to the '85 year, thus causing the 10% high readings? I know the differentials are different, but is there anything different about the transmissions as far as gearing is concerned between the '84 and '85 model years?

Thanks in advance.

I am curious about this as well. I just installed new gears andused speedo from another car. My odometer logs 108 miles for every 100 i drive. Today I went by one of those moble radar machines, sppedo was dead on 25 radar said 23.

I had a lengthly drive on same parkway. I calculated at the end that I need to subtract 8.35% to calcualte mpg. After looking at the radar, if I subtract 8.35% from 25mph indicated I would be 23mph

So what drives them both that could be off? is there something in the speedo that is particular to each model?

I have always wondered why the little shift point indicators were so far off from what my tranny shifts at, maybe i got a gas speedo I do not know

Stock tire sizes. I am big 4x4 guy so I know how tires effect, smaller tires would do it, but i run avery slightly bigger tire.

I do not know what the cluster is out of. I know i put 12 12-48 48-15 gear set in it

I been wanting wheels and tires, I guess i could go bigger to offset everything.

I figured mine out. when i swapped the gears the two inner most gears do not come in kit. I had the two inners from something else, I swapped the two inners and added two 48x12's and I am right on the money with odometer.

Did some more checking on speedo and found it was acrooss all speeds 2mph, so while i had it apart, I twisted it just a tad, and it is now right on as well.

Thanks for the update. I had just assumed that someone had put a rear end out of an '85 in my '84, but hearing that your speedo/odometer issues are practically identical to mine, I'm rethinking that.

When you say you installed a used speedo out of another car, do you mean you replaced the whole cluster, or just the speedo part of it? You might already know this, but you can tell the gas cluster units from the diesel ones by looking at the left multi-gauge unit (oil/temp./fuel). If it has a fourth "economy" gauge on the bottom, you've got a gas cluster. The diesel clusters don't have the economy gauge.

So, just to be clear, what gears did you go from, and exactly what gears do you have in your speedo cluster now? I'd love to get mine working correctly without having to resort to larger tires to compensate.

Sorry to ask you to repeat, but I just want to be clear what gears to get a hold of. I've got a couple extra clusters to look at, but they all had the same issue, so I might have to order some to correct it.

Thanks.

solder points to remove circuit board
 

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

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

Updated photo album here:

W126 Odometer / Speedometer / Clock Repair - Imgur

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

THANKS

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

Indeed!
 

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!!!!