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Old 04-21-2000, 08:24 PM
MikeTangas's Avatar
Senior Member
Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
This little problem has been bugging me for some time, now I want to see if there is a DIY fix or not. The odometer/trip meter on my 280 SEL tends to stick, or stop turning, once the interior warms up. If it stays cool everything works fine, if I park outside on a warm day, it stops working. The speedo functions normally at all times, only the odometer stops.

I noticed this shortly after I calculated my mileage at under 5 MPG after a fill up last year. Now I watch the odometer closely, and keep a note of missing miles for fuel mileage purposes. Of coures the missing miles help lower the insurance, as it showed less than 7,000 miles last year, but I'll never earn a mileage badge at this rate either.

Is there a home remedy for this repair, or am I better served by sending the speedo head off to a speedo shop? Palo Alto Speedo, here in California, will do a complete rebuild of the VDO unit for about $125.00, but if I would prefer to fix it myself.

Also, I have done some exploratory work on the instrument cluster. The knurled nut which should hold the cluster in is missing, so I can slide it out without difficulty. It will come out just far enough that I can see the speedo cable connector, and the wiring harness. I can almost get to the oil line fitting, looks like a 10mm. The line to the temp gauge makes it appear that the temp gauge is mechanical rather than electric, with no obvious way to disconnect for removal.

Are there any hidden tricks to getting the cluster out far enough to gain easier access to the connections and fittings? Where should I disconnect the temp gauge line? Would it allow the cluster to come out further if I disconnected the speedo cable at the transmission?

Thanks for all the help from this group. And all you diesel head, keep asking your questions...I am learning a lot, getting ready for when I change over to an oil burner(hopefully by the end of the year).

Mike Tangas
73 280 SEL
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Old 04-21-2000, 08:57 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I would advise sending it to the speedo shop. There are a number of things they will do to improve the overall quality and life of the unit. The speed cup and wheel support bushing is probably worn and they will replace it and adjust endplay. This was always a source of noise and vibration.

They also will clean, lube properly, and calibrate the rest of the speedo. They will know how to tell if the number wheel gears are worn to the point they catch, which is the most common cause of the odometer drive gear getting loose on its shaft.

For years before we started doing them professionally I used to fix the wheel slipping by sliding the shaft out while sliding in a drill bit to support the number string. I would line up the shaft to see where the pot metal drive gear would eventually be. I would take a small sharp punch and a vice. Laying the shaft on the groove between closed vice jaws I would in effect knurl the shaft by making six or seven small dimples with the punch. I would then slide the shaft back in pulling the drill bit out while still supporting the numbers. When I got to the knurled section I would squeeze it through the gear with the vice, Slowly! till the right depth for free play.

We now do it with new parts and total diassembly.

The temperature cable is a hollow tube carrying a gas to a bulb in the head. It is totally manual and will either have to be removed from the cluster or the cylinder head as it can't be separated. The speedo cable can be lengthened by removal from trans and pushing the cable through.

It seems to me that we always did this work from beneath and behind. On the worst restricted ones we had to drop the emerg brake handle and bracket.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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Old 04-22-2000, 08:14 PM
Posts: n/a

I would suggest that you follow Steve's advice and send it to a speedo shop.

My speedometer began doing just what you describe, and then it got to a point where the trip odometer was preventing the main odometer from turning. If you get to this point you can save the main odometer by removing the spur gear between the main and trip odometers. You will then, of course, lose the use of the trip odometer. But again, if it's not an undue financial burden, have the speedometer overhauled by a reputable shop.

Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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Old 04-23-2000, 01:21 AM
MikeTangas's Avatar
Senior Member
Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
Thanks for the replies.

After posting the question, before checking for any replies, I had decided I would farm this job out, Steve's reply and Larry's concurrance only strengthened the arguement to the wife. If Palo Alto Speedo, does what they say they do for $125.00, then it's worth it. Over the phone they even told me they clean the tenths dial, so you can tell the numbers are red, as well as replace damaged parts with new. I wonder if the speedo shop would be able to calibrate the speedo head to the tires I'm running? The speedo does show about 5-7 MPH more than actually going. Or do you think that could be additional damage in the gear clusters? Either way, I'll ask when I send it off.

Someone told me that all I needed to do was open the speedo head and with the smallest bit I could find, drill a hole into the gear collar and part way into the shaft, then break off the bit. This sounded a bit much for a cure, and I'm glad I asked here before acting on odd sounding advice.

Now all I have to do is find the time to pull the cluster and speedo head. I'll probably try to keep the remainder of the gauges connected, so I can still drive the old girl. Not that we're short on cars, I just hate having to fill the tank on the Suburban with today's gas prices . I'll let y'all know how it turns out. Thanks.

Mike Tangas
73 280 SEL
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