HOW-TO: W126 Odometer Repair, Clock Capacitor Replace
 

Hey everyone,

My green 300SD's odometer failed yesterday so I decided to investigate. From what I've learned here the drive gear and one of the other gears fail. Sure enough, this was the case for my 300SD as well. What I didnt see on here was too many pictures so I decided I'd take some and post up..

Step 1) Remove Instrument Cluster from Car.

Step 2) Remove Speedometer section from cluster.

Step 3) Remove plastic backing plate via small screws.

http://i.imgur.com/Ihtvol.jpg

Step 4) Inspect your gear train for damage.

As you can see in my second photo my drive gear is missing several teeth as well as the gear that it meshes with.

http://i.imgur.com/Y9BSRl.jpg

http://i.imgur.com/aKoELl.jpg

Step 5) Source replacement gears. You can either buy them for ~$65 from Odometer Gears - WELCOME or if you have a spare speedometer see if the gears are compatible. Luckily I happened to have a spare 560SEL cluster with the same tooth count gears so I simply swapped them over.

Installed replacement drive gear:
http://i.imgur.com/KUDD1l.jpg

http://i.imgur.com/qpGOCl.jpg

Finally:
http://i.imgur.com/xleIbl.jpg

Step 6) Replacing Capacitors.

Since you have the speedometer out, you might as well replace the capacitors. For my 300SD, there were three. The replacement were easily obtained from Radioshack for about $4.50 or so.

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 that you are free to replace the capacitors, the values are as follows: 2 x 220uF @ 6 V, 1 x 47uF @ 16V. RadioShack carried ones that were rated at 35V so we were set.
http://i.imgur.com/luaLLl.jpg


Here are my replacements installed:
http://i.imgur.com/3Msz7l.jpg

Step 7) Reassembly

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.

Replacing Clock Capacitors
 

My buddy (source of the spare 560SEL cluster) was having clock troubles so I told him I'd replace the capacitors in this one. I did the same for the 300SD as the cluster was on my desk. The procedure is pretty straight forward, just be careful with the units.

Step 1) Remove clock/tach pod from cluster

Step 2) Remove circled screws and desolder as indicated by arrow:
http://i.imgur.com/uinxXl.jpg

Step 3) Remove face screws.
http://i.imgur.com/O2mesl.jpg

Step 4) Replace the capacitors

Flip unit over carefully, giving yourself access to the back of the clock and its capacitors.

http://i.imgur.com/Og8Jpl.jpg

Now, my 300SD had two capacitors whereas the 560SEL only had one. Both were 100uF/16 volt capacitors. I had previously ordered a batch of 100uF/25 volt capacitors from Mouser so I was set. Radioshack should carry 100uF/35 volt capacitors as well.

560SEL Old:
http://i.imgur.com/DB8YFl.jpg

300SD Old:
http://i.imgur.com/YGf6Jl.jpg


560SEL New:
http://i.imgur.com/RZJgfl.jpg

300SD New:
http://i.imgur.com/GKBmil.jpg



Step 5) Carefully reassemble the unit.

Be sure to fully seat everything and solder that one point that we de-soldered in order to gain access to the capacitors. After that, put your screws back in and put the pod back into the cluster, and you're done!

Hope this helps some of you out there.

If you've any questions let me know.

-Kris

Nice clear writeup JamesDean. Thats pretty well what we have come to expect from you though.


For those unfamiliar, a capacitor of higher voltage can almost always be used if there is space to do so. If a capacitor is polarity sensitive the plastic surrounding it will be very plainly marked with either a + or - symbol.

Good stuff Kris.

Well this was short lived. My dad said his odo/trip failed yesterday and sure enough the "replacement" 12-tooth drive gear I sourced from a 560SEL had broken in half.

The main 48x12 gear was healthy though. So I think my buddy has another cluster I'm gonna swipe for yet another drive gear.

http://i.imgur.com/K9AfCl.jpg
http://i.imgur.com/WgLyEl.jpg
http://i.imgur.com/izyvDl.jpg
http://i.imgur.com/KBNnIl.jpg

I ended up just buying a single 12-tooth drive gear replacement from odometergears.com. It was like $30 all said and done.

Anybody know if the r129 has a 12 or 16 tooth gear? That website advises pulling the cluster to find out, but I'd rather know so I can order something pronto. Is there no way to know via prod date or VIN?

concerning the clock repair, my Radio Shack only had 1 F35V100uf35. TNBob said the voltage didn't matter so I also purchased a F50V100uf50. Should this work or do I need to find a second F35V100uf35? Physically they are the same size.

thanks!

As long as the voltage exceeds that of the original you are good to go!

Thanks Kris, I'll see what happens.

Althouth my tach is working, it would only make sense to replace the capacitor while things are apart. Accessing the capacitors on the clock has been well explained and is fairly straight forward once things are apart. The tach capacitor however doesn't appear to be accessable without removing the needle and faceplate. Am I missing something? I'm very apprehensive about removing the needles.

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.

The cluster removal was prompted by the recent odometer failure. Speedometer still works. What I think I found was the green gear on the end of the shaft that runs through the odometer was slipped out and not engaging the white screw type plastic shaft. After playing with it a bit the green gear appeared to still be on the metal shaft but the whole shaft assembly had shifted to the left when viewing from the front of the meter. It appears the dark grey gear on the right side of the odometer is no longer firmly attached to the metal shaft allowing the shaft to shift to the left. After carefully manipulating the green gear, was able to get the gear and shaft to slide back in to place. I did not attempt to spin the meter to confirm it would work when in the correct place, but I would be surprised if it would as I thing the grey gear needs to be attached firmly to the shaft also? I don't think any of the gears are missing teeth but I can't really see it well as the faceplate blocks the view.

If indeed this is accurate, does the faceplate have to be removed to "operate" on the odometer? If so, how does the faceplate come off without removing the speedometer needle? If the needle must be removed, what's the best technique to accomplish it? If the "operation" is successful, how is the needle returned in its proper position?

As stated before, I'm really apprehensive about removing the needles.

Also, is my Weller soldering gun capable of r/ring the capacitors or do I need a smaller soldering iron? Never messed with circuit boards before.

Question about capacitors
 

If the speedo works but the odometer and trip do not, what can be the problem besides the gears? I have taken apart twice, inspected each gear and spun the stator motor wheel by hand and the odometer works fine. Can a capacitor or board cause the problem? Not sure where to look or how to test.. Appreciate any ideas.

Thanks,

Bill

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!!!!

Gears Source
 

Btw, I got mine from this place: Mercedes Odometer gears
$17 for the set of three (and they even had the rare 14/48t in stock which I needed).

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.

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!

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

board looks differently
 

Hi,

I finally came around to work on the odometer gears and the watch.
It was actually quite easy to find the 5 soldering spots to remove the speedometer from the board as someone has done that before (I guess, when they exchanged the speedometer with an US version).

I realized that the capacitors and also the board layout look very different from yours. I only had one 47uF and one 220 uF and both looked very modern. I thought it wouldn't make sense to replace them as they still looked fine.

As for the watch, I have a 200ohm resistor around which it looked pretty black. However, I could test it and so I assumed it must be ok.

What is your opinion on replacing these resistors and capacitors?

Thanks!

I would replace those capacitors for certain. The one says W. Germany on the side of it, I believe which puts it at the minimum of 20 some years.

If the resistor(s) don't look damaged or harmed in any way I would not bother replacing them. The capacitors are what can age and fail.

all is good at the moment
 

Thanks for the recommendation!!
The next time I'll have to work on the odometer, I'll replace those.

So now my watch is finally keeping the right time!!!
I had most of the connections re-soldered together with lubing both the gears and adjusting mechanism seems to have helped...

Very happy and thanks for all your help!

speedometer is now off :(
 

I can't believe it!
I was so happy that the clock is finally working accurately, but now I realized that my speedometer is about 10-15 mph too fast (depending on the speed).

Could this be in connection to the old capacitors? Or what else could it be?
I replaced the gears (but miles are correct as tested with GPS) and soldered the connections to get the speedo-/odometer off the board.

Thanks for your continued help!

Step-fan,
I was thinking about your 10-15mph error and was going to try to help, but I realized I didn't know what kind of car you have. I tried to fine that information in your previous post but couldn't find anything. So I'm sorry, I can't help. I gave some advice one time when I didn't know the exact car and was wrong. I gave bad advice which was completely wrong. And as we know wrong advice is a bad thing.

Paul

If the miles are correct we can conclude the speed signal is correct and the problem lies in the circuit that controls the speedometer needle. I would start by replacing the caps. They might not be providing enough power to drive the little motor that runs the speedo needle. I'd also reflow all the solder joints on that board as well. There are not a huge amount so it should be fairly straight forward.

1989 300SE Euro
 

Hi Paul,

thanks a lot for trying! I greatly appreciate your efforts and fully understand your concerns about wrong information given. However, I personally think every reader should be able to judge whether that particular advise applies to their cars and should never taken any advise as guaranteed as every situation is different. I have been given 'wrong' information before, but there's nobody else to blame besides me as it was my very own decision to follow the advise.
That's part of the risk you're accepting using an online forum, and if I wasn't accepting that risk, I simply have to bring the car in.

Anyways, my car is a 1989 300SE EURO with ASD and France-specific rear diff ratio of 3.07.

I hope that helps.

Thanks,
Stefan

Thanks!
I was thinking the same, and I will report back whether that helped.

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.

o.k. before
 

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....?

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.

This is a great thread, thanks for the info!:D

During the summer my 420's clock had been intermittent, now that its sub zero temps, the clock seems to be working most of the time. But its lost my trust in its accuracy. The cold has caused the caps to work again, but its time for some fresh stuff after nearly 2-1/2 decades.

My 560 is stored for the winter, im planning on retrofitting one of those nice EL backlit cluster inserts. And even though the clock works in that car, a cap refresher is in order; I might as well when the cluster is apart.

Problem solved!
 

Hi,

good news: the speedometer issues have been resolved!
I changed the capacitors earlier today (and learned a 220uF, 50V one is far too big :( ) and the speedometer is super accurate again (probably even more accurate than GPS.. ;-)) ).

The only thing that is now a little bit bothering, I hear a constant click-click-click sound from the odometer. The movement of the number is not fluent anymore, but more like in small increments. The odometer is still accurate, though.
Could this be a sign of a faulty motor or of another part on the board that might have gone south??

Thanks a lot for your continued help!

The new gears are nylon or plastic whereas one of the original gears was made of a more resilient clear plastic. I believe the new gears are the source of the click-click noise and I haven't been able to find a set of gears that are made of the same material as the original gears. Mark

Job done.
 

Hi Mark,

thanks for your answer. I think what you're describing is exactly what is going on. I found a similar post reporting exactly the same issue:

Odometer Gears--Great Solution, Just Noisy - Mercedes-Benz Forum

So I opened everything again today and took the cover from the magnet and the magnet apart and lubed (with a teflon-based lube) the whole spindle from one side to the other.
Also, I added some high pressure bearing lube to the gears and so far it looks - and more importantly sounds good!!!

Everything is still very accurate (checked by GPS again), so I'm pretty happy now... :-))

Off to the next project.....

I didnt notice any additional noise in our 300SD's gears but then again it is a 300SD and its not an overly quiet car... I think thats the only car I've ever had to replace gears on..