Speedometer malfunction - PeachParts Mercedes-Benz Forum

Mike123 · #1 03-10-2004, 10:19 PM

My speedometer is sitting on 85 mph even when the car is standing still. The vehicle is an '81 300CD. The odometer and trip odometer seem to be working properly, but the speedometer does not move except in reverse. In reverse the needle will move to about 70 mph and when I stop the needle will slowly move back to 85 mph and sit on the peg.

Any ideas. I didn't find much on a search of the site.

#2 03-11-2004, 06:38 AM

This is not a common speedometer failure mode, it is usually the odometer that fails. I expect that your best bet is a salvage yard speedometer. It is easy to replace by pulling the cluster and changing it from the back.

If you want to duplicate the odometer setting, file off the swage around the perimeter of the odometer shaft, carefully pull out the shaft, set the odometer to the correct mileage. Then put the shaft back in and brad it again so it won't come out.

Good luck,

Pete Burton · #3 03-11-2004, 08:04 AM

I've never looked at the inside of a MB speedometer, but maybe there is a small, delicate torsion spring that returns the dial (like on other speedos) - if it broke when it was more than halfway around the dial, it would fall all the way forward. Then, it wouldn't move unless the dial saw magnetic impulses going in reverse. I agree with Larry that you have to pull it, but when you do, check for this spring, because if it broke or came loose at one end, you MAY be able to epoxy it back in place and fix it. Good luck!

Mike123 · #4 03-11-2004, 11:48 AM

The needle on the speedometer has been shaky all winter, especially between 40 and 60 mph.
I ordered a used speedometer this morning and should have it in a couple of days. I'll let you know what I find when I pull the cluster. I didn't want to pull the cluster without the replacement part. It may well be nothing but a broken spring, and I may repair the problem, but I want the part in my hands before I start the job.

Stevo · #5 03-11-2004, 12:55 PM

Mike123

Be sure to slack off the spedo cable in the engine compartment which wll give you a little extra room back there. Good luck

Mike123 · #6 03-15-2004, 03:21 PM

I ordered the speedometer from Bridgeville Auto in Bridgeville, Del. It was $85 including the shipping. I ordered on Friday midmorning and had it at noon today, Monday. It was very well packaged; double boxed with packing material around and inside the inner box. They sent the whole cluster. It only had 64,*** miles on it. The needles are that nice deep orange/red. It looks like a new one. It took me a little less than an hour to pull the old one and install the new one. Everything works great, including the rheostat or potentiometer, the clock, all lights and gauges. My temp gauge is not bouncing around like it was. It would jump up to just under 100 and back down to 85 and stop in between sometimes. Now it is registering the same temp as my laser thermometer does when pointed at the housing (at least within a couple of degrees).
Thanks for the help. It is great to get so much good advise and the heads up that only someone who has done the procedure before would know. I thought it was the speedometer itself since the odometer still worked, but it is reassuring to get one's diagnosis reinforced.
Thanks to all who responded. Sorry for the long post.

Mike123 · #7 03-15-2004, 04:44 PM

For once I was lucky. I found out about the factor number from a friend after I ordered the speedometer. The speedometer came from the same model and year. It has the same number on the back! Besides the money I saved, I saved the hassle of taking it to a shop to have the repair made and the down time. I'm not sure, but about everything else for this 23 year old car is hard to buy or have rebuilt locally. We have the dealer and a couple of import parts dealers, but speedometer shops, drive shaft rebuilders and other specialty shops who work on MB are harder to find.

Mike123 · #8 03-16-2004, 07:15 AM

I drove the car after dark last night. What a difference as far as the cluster lights. It was far brighter than it has ever been. The "new" cluster is almost like new as I stated before. The needles and numbers are much brighter and the lights seem to be much brighter. I actually turned the potentiometer down! It was a little too bright for me. Wonderful!! Again, thanks for the advise.

Mike123 · #9 03-16-2004, 07:20 AM

Oh, I forgot to add one thing. As has been stated before, the on line sellers are great for certain used or new parts. As far as used parts go, I have not been able to find a "local" supplier. The only import recycling yard around here has nothing older than 1990. That puts me out of their market. Adsit is in Muncie, only about one hour away, but they wanted $195.00 for the speedo, with a 10% discount for ordering by fax, plus shipping. I have ordered a couple of new things from them about four years ago, and was satisfied, but $120.00 is a substantial difference, and I hardly think I could have gotten a better part.

Cr from Texas · #10 04-21-2008, 01:15 PM

Quote:

Originally Posted by Mike123

The needle on the speedometer has been shaky all winter, especially between 40 and 60 mph.
I ordered a used speedometer this morning and should have it in a couple of days. I'll let you know what I find when I pull the cluster. I didn't want to pull the cluster without the replacement part. It may well be nothing but a broken spring, and I may repair the problem, but I want the part in my hands before I start the job.

Mike,
Are you still following the forum? If so, I found your thread and would like to know if you found what was wrong with your old speedometer.

Last weekend, I did several repairs to my 1983 300D turbo including fixing the clock and painting the needles in the cluster. Replaced the cluster and everything works except the speedometer. The odometer and the trip meter work so I don't think it's the cable. If I hit the dash above the cluster, the speedometer will sometimes work.

Anyone have any ideas? This unit was a black box on the back with two electrical leads. I've checked the connection but still need to check the wires to see if I crimped them putting the cluster back. I noticed that the speedometer seems to have the same type capacitor that I replace in the clock. Any one replaced any speedometer circuit components?

Ideas, suggestions???

Charles

Mike123 · #11 04-21-2008, 06:18 PM

My speedometer had a broken spring. It was easier, cheaper and better to replace mine. It doess't sound to like the same problem that you have. Good Luck.

bgkast · #12 04-21-2008, 07:42 PM

The paint is causing your needle to stick to the pin Charles. I had the same problem after painting my needles too. I solved the problem with a thin coating of oil on the pin.

Cr from Texas · #13 04-22-2008, 02:35 PM

Quote:

Originally Posted by bgkast

The paint is causing your needle to stick to the pin Charles. I had the same problem after painting my needles too. I solved the problem with a thin coating of oil on the pin.

Ok, I'll try that. How long did you wait before doing this? Looks like once it dries it would be ok. I'll need to wait till the weekend anyway.

Charles

konstan · #14 02-09-2010, 11:01 AM

Quote:

Originally Posted by Cr from Texas

Last weekend, I did several repairs to my 1983 300D turbo including fixing the clock and painting the needles in the cluster. Replaced the cluster and everything works except the speedometer. The odometer and the trip meter work so I don't think it's the cable. If I hit the dash above the cluster, the speedometer will sometimes work.

Have the same problem in my 300D, and it's been months since I painted the needle.

Did you ever try the oil on the needle trick? Was it really paint that was making it stick? Or some sort of magnetic interaction?

My next step is to try to wrap the stop post for the needle with something that is not subject to magnetism or static electricity... like a small aluminum bushing or something of that sort.

Cr from Texas · #15 02-10-2010, 11:42 AM

Sorry, I should have posted back the result.

The oil on the needle stop solved the problem.