Does the odometer have to work in order for the speedo to work? - PeachParts Mercedes-Benz Forum

nels2173 · #1 05-12-2013, 02:11 PM

I just got a 1987 300sdl and the speedometer/odometer are both not working, Ive searched the forums and found several extremely helpful posts about possible causes for the odometer failure and resources to get that repaired. Does the odometer have to work in order for the speedometer to work? These speedometers are electrical as far as I can tell, any advice would be much appreciated. where should I start? Pulled cluster out things look ok there nothing seems to be disconnected.

thanks

nels2173 · #2 05-12-2013, 02:15 PM

I should add the only idiot light on is the abs light, not sure if that tells me anything, I have read about the speed sensor on the transmission? could that be blown in some way, any relays I should be checking? Everything else works fuses check out ok.

MTI · #3 05-12-2013, 02:23 PM

In 87, the VDO speedo was cable driven and the odometer is a clockwork gear driven mech. The VDO odometers of this period, in MB, Volvo, Porsche, etc., are well know for their tendency to strip or fall out of alignment, especially when owners would reset to zero when the car was in motion. You may have a busted cable than runs from the back of the cluster speedo drive to the transmission.

nels2173 · #4 05-12-2013, 02:44 PM

According to this thread there is no cable

Odometer and Speedometer stopped today 126

w123fanman · #5 05-12-2013, 04:03 PM

Speaking of broken odometers, the one in my 190D has stopped functioning. It has however moved forward 1 mile since I got the car (I've done less than a thousand miles I believe). Would this indicate a stripped gear in the assembly?

Mr.Kenny · #6 05-12-2013, 04:23 PM

The speedometer is independent of the odometer; but both work off the turning speedometer cable.

Pooka · #7 05-12-2013, 05:34 PM

just a bit of info on VDO speedos...

The cable will break. The only way to know if the cable is turning is to watch it. I usually pull out the instrument panel and take a friend along for a trip around the block. They watch to see if the cable turns. If not then replace it.

Cable is turning? Then the magnet inside the speedo needs to be checked for movement. You have to remove the speedo, which is just a few screws or bolts, from the instrument panel, and then study it for a bit to understand how to remove the back cover. Once the cover is off see if the magnets are rotating freely. If not then they are frozen and nothing will unfreeze them to the point that your speedo will ever be accurate. Therefore it is time to get a new one or at least a working one.

If the magnets are turning then spin them around and see if the speedo registers any speed. If not then chunk it and get another one since they are too hard to tear into and too easy to find on Ebay.

If the speedo is working and the odo is not, which is usually the case, then do a web search for 'replacing odo gear'. This is easy and cheap.

Brian Carlton · #8 05-13-2013, 09:39 AM

The speedo can function without the odometer. That is the most likely scenario when the gears in the odometer fail.

When both don't work, you might have an instrument problem or might have a problem with the pickup.

The unit is not driven by any cable.

nels2173 · #9 05-13-2013, 11:26 AM

Is the pickup on front wheel or transmission?

Brian Carlton · #10 05-13-2013, 11:37 AM

Quote:

Originally Posted by nels2173

Is the pickup on front wheel or transmission?

Does the cruise control work?

Do the brake lights work?

Do the backup lights work?

nels2173 · #11 05-13-2013, 11:43 AM

Cruise, no

Brake light and backup lights do work

Brian Carlton · #12 05-13-2013, 11:56 AM

Quote:

Originally Posted by nels2173

Brake light and backup lights do work

Have you personally checked?

nels2173 · #13 05-13-2013, 11:59 AM

I've had someone else check them, and I can see myself the rear brake light in the rear window is working but I will check again what would this tell
Me

Brian Carlton · #14 05-13-2013, 12:12 PM

Quote:

Originally Posted by nels2173

I've had someone else check them, and I can see myself the rear brake light in the rear window is working but I will check again what would this tell
Me

It would tell you the fuse is bad.

JamesDean · #15 05-13-2013, 12:15 PM

On a 300SDL? the speedometer was cable driven? I was under the impression that all 126's were electronically driven..

There is a connector located just to the right of the accelerator pedal. This connector has a few things in it..among them is the speed signal wire and the reverse lights...these both come up from the transmission, in a 560SEL i was working on..this connector was taken apart...the odo/speedo/backup lights did not work.. i would check that..