HOW-TO: W126 Odometer Repair, Clock Capacitor Replace - Page 4 - PeachParts Mercedes-Benz Forum

Das Benz · #46 01-02-2014, 09:42 PM

This is a great thread, thanks for the info!

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.

steh-fan · #47 01-04-2014, 10:26 PM

Quote:

Originally Posted by JamesDean

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.

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!

hookedon210s · #48 01-05-2014, 07:34 PM

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

steh-fan · #49 01-05-2014, 09:09 PM

Quote:

Originally Posted by hookedon210s

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

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.....

JamesDean · #50 01-05-2014, 11:12 PM

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..

4thesporty · #51 03-05-2014, 10:55 AM

A while back my odometer stopped working as well. I ordered replacement gears from odometergears.com, installed them and it worked OK for a while.

Then it seemed it would work sometimes, then not work anymore. I inspected and lubed the gears a couple of times with no real change. Recently the odometer stopped working all togather. I found this thread and embarked on fixing mine as well.

The gears I installed were working just fine as I can sping them and the odometer moves fine, which makes me believe I have an electrical problem:

Using some solder wick and a good iron, I unsoldered the five points that hold the speedometer to the unit:

I found this:

Unlike the OP, my 85 300SD only has two capacitors. One I can clearly see as 220/6, the other one I can't make out for sure, but I beleive it is 1.7/16. Does this seem right. I know very little about these. I plan on picking some up at radio shack over lunch and putting this back togather.

Any good eyes here that can make out the numbers on the smaller cap?

Thank you in advance!

steh-fan · #52 03-05-2014, 11:35 AM

To me it looks like 47, which would also make sense because that is what the others had, too.

RadioShack might work, but I liked the 105C ones I got from a real electronic shop. RadioShack has them online, unless you have a RadionShack with a huge selection nearby.

Hope that works!

JamesDean · #53 03-05-2014, 12:21 PM

I would guess 47 too.

I repaired an 86 300SDL speedometer and it had a 47 uF cap in it. 47 and 220.
W126 Speedometer Repair - Imgur

seebeexee · #54 03-05-2014, 01:08 PM

Quote:

Originally Posted by 4thesporty

Unlike the OP, my 85 300SD only has two capacitors. One I can clearly see as 220/6, the other one I can't make out for sure, but I beleive it is 1.7/16. Does this seem right. I know very little about these. I plan on picking some up at radio shack over lunch and putting this back togather.

Any good eyes here that can make out the numbers on the smaller cap?

Thank you in advance!

My '84 300SD only has two capacitors: a 220uF and a 47uF also. It looks like the markings on your capacitor are stamped off-center resulting in the side of the "4" not showing up. Funny, though, because it does look like a perfect "1".

4thesporty · #55 03-05-2014, 02:00 PM

Thanks for the confirmation on the numbers. I was able to pick up both caps during lunch, a 220 and a 47 uF 35w. I'll get them soldered in this afternoon and get a test drive this evening.

I do have some nice test equipment here at work and I am curious how the old ones measure when I get them out.

4thesporty · #56 03-05-2014, 03:05 PM

Hmmmm.

I got the new ones soldered in:

I used these radioshack part numbers:

I took the old ones, and with a BK precision 875B meter I found that both of the original caps measured pretty close to what they should be. The 220 uF cap measured 232 and the 47 uF cap measured 46.

I'll get this assembly back in the car this evening and hope for the best. If this does not get my odometer going, what is the next item that could be the culprit? I do have new gears and when I spin the drive gear with my fingers the odometer does move fine. Could the motor be bad? Can you replace that?

4thesporty · #57 03-05-2014, 06:52 PM

Well, odometer still does not work.

I'm open to any suggestions.

Sent from my Windows Phone

Unshriven · #58 11-03-2014, 03:56 PM

Quote:

Originally Posted by TnBob

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.

Is there an easy way to tell how to orient the capacitors? I assume, like a diode, the longer tail is positive?

JamesDean · #59 11-03-2014, 03:57 PM

Yes the longer lead on the capacitor is positive. On the short lead side there should be a white strip or arrow on the capacitor's body. This indicates the negative side of the capacitor. Generally the boards are labeled where + should go.

kamran49 · #60 01-10-2015, 12:27 PM

Dear JamesDean
I have a W126 280SE 1982 and my speedometer overestimates about 40%. I have changed 2 capacitors (it have only 2 caps 47 and 220) but problem did not resolved. all gears are in good health and the movement is smooth. please let me know your suggestions.
Thank you in advance.
Kamran