Odometer not working 85 300SD - PeachParts Mercedes-Benz Forum

yuke · #1 10-14-2015, 03:47 PM

My odometer stopped working again. I on my 85 300 SD it stopped a few years ago and I got a replacement from some company down south in Georgia I think it worked for a few years and quit again. Well when I went to disassemble it the speedo needle went flying and I still can't find it but when looking at the rest of it all the gears look good and it seems like it records milage like it should so what could be wrong that it does not record the miles? The speedometer works. Does the spdometer and odometer work from electrical impulses? It did seem where the speedometer plugs in the back that pin seems lose could that be the problem? Does anyone know what makes these these work or where I could get a replacement at a reasonable price as I have not found the speedometer needle yet. My part # of this unit is 126 542 48 01. Any one have one laying around that they would be willing to part with? Or could my problem be that it is not getting the proper signal to record milage but speedometer did work fine.

TX76513 · #2 10-14-2015, 04:56 PM

I don't think it will let me put a link in here. BUT if you are handy with an ohm meter Google VDO Troubleshooting guides. Very good detailed information.

mach4 · #3 10-14-2015, 07:40 PM

The odometer and speedometer operate off the same signal. If the speedo is working your sensor and wiring are fine. It's pretty likely that your smallest gear is just spinning on the shaft. The signals trigger a stepper that drives the gears. If the stepper is blown you'll need a new speedo unit.

The speedometer needles are the same for many MBs so just go out to the junk yard and grab one.

yuke · #4 10-14-2015, 08:23 PM

Thanks mach4 Im not having a good day when I was taking it apart the needle on tne face came off very hard using 2 spoons and when it left go boy did it fly still have not found and am giving up after 8 hrs. of searching and to make matters worse according to vstech the 85's have a 2.88 rear and 84's and earlier had a 3.07 rear so I would have to get a unit from an 85 so looks like Im gonna be w/o a speedometer,odometer for awhile. Seems I cant remember or locate the last people that worked on this as it was a few years ago they swapped my old one out for I think less then $75 they were down south somewhere I thought Georgia but on my search I have not found them. Thanks for the help Mach4.

yuke · #5 10-14-2015, 11:24 PM

The latest on my odometer problem is I looked closer as what the problem could be and yes there is a bad gear in that the teeth are chewed up. It is the gear that is driven off the real small one it looks like it has 48 teeth on the one side and 12 teeth on the other side the 12 are chewed up pretty bad. So I guess if I could purchase this one gear and locate a speedometer needle I would be good to go. I will be searching for both tomorrow any one know where I could get the needle please let me know. Thanks

Junkman · #6 10-14-2015, 11:37 PM

Here's a place to buy gears.

Gears - Designatronics Inc.

My issue is that I don't know what size gears to buy and mine are too messed up to count the teeth. Odo Gears charges a lot (more than I'm willing to pay) for their knowledge.

Is the electrical pick up for the speedo dependent on the differential ratio? My 84 reads too slow and different diff ratios (incorrect pick up) would account for that.

There is a helpful thread I think titled "Fix your speedometer for pocket change"

mach4 · #7 10-15-2015, 12:50 AM

Quote:

Originally Posted by yuke

The latest on my odometer problem is I looked closer as what the problem could be and yes there is a bad gear in that the teeth are chewed up. It is the gear that is driven off the real small one it looks like it has 48 teeth on the one side and 12 teeth on the other side the 12 are chewed up pretty bad. So I guess if I could purchase this one gear and locate a speedometer needle I would be good to go. I will be searching for both tomorrow any one know where I could get the needle please let me know. Thanks

I'd suggest getting all the gears. They're not all that much more expensive. When one goes, it pretty much means the others are brittle too, and getting ready to go as well.

I attempted to change just one gear on mine when it stripped and within 2 months another one went - so I not only bought the failed one but a complete set too along with the one that failed first. It's no fun going in there and working on those, so it really makes sense to get a new set and do it once.

optimusprime · #8 10-15-2015, 06:06 AM

The trip counter in the speedo is manual operated from the speedo cable .I have replaced a few of these in the time of owning MB .If you Google this you will find lots of information on how to do the job and what replacment parts you will need . Also on your Ebay usa will have the replacment gears .The one web site will show you how to go about it .And do come with instrctions . And your on one of the best information sites at the moment ,at the top of the page check out Tech info .

optimusprime · #9 10-15-2015, 06:12 AM

Yuke did you take spring pressure off the pointer by lifting it over the stop ,and marking its resting possition ? should have done this before you pulled it off with spoons .If not the speed will be out on refiting it.

optimusprime · #10 10-15-2015, 06:19 AM

Yuke google this -DieselGiant.com Odometer . This is how i started on my speedo.I know its a w123 but idear is the same i know its not you model but the idear is just the same. Wish i was there i could help you get it up and running.

yuke · #11 10-15-2015, 08:26 AM

I have learned a lot while trying to repair my odometer it was previously repaired by benz bin about 3-4 years ago I swapped my old one out and got a replacement and I think they used a gear made of inferior material in that it only lasted this long. What I also want to caution any one else doing this is if you do take the needle and face off be very careful when prying up on the needle because mine went flying and after 8 hrs. of looking for it in my living room I have given up. The 85 300sd signal is all electric and has 2.88 rear compared to the earlier ones 3.07 rear which would throw you milage off also your size wheel could throw it off also as I have the 86 (15") wheels on mine but my milage and speed were close enough if not right on. I did try to purchase a gear from gizmos for $2.36 which is about what it should cost and found out yes they are out of stock on that gear which has 12 and 48 teeth. I refuse to pay $25 for that little gear and instead am looking for a used whole speedometer from a salvage yard. I will let everyone know how it turns out. It is very simple to get at the main drive gears on the 85's I would not have had to take the needle and face off but I did not know this when I started. Thanks for all the replies hope to get this working soon.

vstech · #12 10-15-2015, 09:30 AM

I have several SD speedometers I could pop off a needle for ya. No 85s so I can't swap entire to ya... I do own an 85 so I could pull it apart and count the teeth on the gear for you.

JamesDean · #13 10-15-2015, 12:48 PM

Quote:

Originally Posted by yuke

I have learned a lot while trying to repair my odometer it was previously repaired by benz bin about 3-4 years ago I swapped my old one out and got a replacement and I think they used a gear made of inferior material in that it only lasted this long. What I also want to caution any one else doing this is if you do take the needle and face off be very careful when prying up on the needle because mine went flying and after 8 hrs. of looking for it in my living room I have given up. The 85 300sd signal is all electric and has 2.88 rear compared to the earlier ones 3.07 rear which would throw you milage off also your size wheel could throw it off also as I have the 86 (15") wheels on mine but my milage and speed were close enough if not right on. I did try to purchase a gear from gizmos for $2.36 which is about what it should cost and found out yes they are out of stock on that gear which has 12 and 48 teeth. I refuse to pay $25 for that little gear and instead am looking for a used whole speedometer from a salvage yard. I will let everyone know how it turns out. It is very simple to get at the main drive gears on the 85's I would not have had to take the needle and face off but I did not know this when I started. Thanks for all the replies hope to get this working soon.

You could also try stock drive, they have LOTS of gears:
Gears - Spur Bevel Helical & Miter Gears, Worm, Anti-backlash Gears from SDP/SI

If you buy a used speedometer you might just run into this issue again down the road. I mean if they haven't been replaced they're all pushing 30 years old now.

I strongly advocate for buying good quality gears. $25 is well worth it if you don't have to visit this issue ever again. I mean think of how much time and effort you've invested all ready?
www.OdometerGears.com has been my go-to for odometer gears since I started working on them. Never had any issue.

I've had people send me speedometers with cheap low quality gears before. In one case the gears didn't even mesh properly, either they sent the wrong one or idk..

JamesDean · #14 10-15-2015, 12:49 PM

Quote:

Originally Posted by Junkman

Here's a place to buy gears.

Gears - Designatronics Inc.

My issue is that I don't know what size gears to buy and mine are too messed up to count the teeth. Odo Gears charges a lot (more than I'm willing to pay) for their knowledge.

Is the electrical pick up for the speedo dependent on the differential ratio? My 84 reads too slow and different diff ratios (incorrect pick up) would account for that.

There is a helpful thread I think titled "Fix your speedometer for pocket change"

What car are you working on? I've got some pics I've taken over the years with gears and such that might be what you're after.