Mercedes-Benz Forum banner

1 - 9 of 9 Posts

·
Registered
1985 300cdt
Joined
·
7 Posts
Discussion Starter #1
My speedometer has gotten progressively worse over the last couple of years. My faithful mechanic says it is typical for the vehicle with new speedometers having the same issues. So I just adjust the speed mentally. Now I off about 7mph at around 40 and 15mph around 75 on the freeway. Any suggestions out there as far as reliable replacements or repairing mine?
 

·
Registered
Joined
·
424 Posts
Fix it. There is a shim under the needle with a slit in it. You can adjust the pre stress of the needles spring there. Take a tiny srew driver, a gps and connect the speedo and the oil instrument without the rest of the cluster.

Takes about 2 hours if you do it the first time.



It's a W124 speedo, the W123 is the same, just without the plastic. You can see the shim in the center of the spring.




It works.
 

·
Registered
1985 300cdt
Joined
·
7 Posts
Discussion Starter #5
Thanks for the detailed tip. I may see if my mechanic has a GPS and wants to give it a try. Or I can work with a friend who does. Tach does not function either but I can live without that unless you have a fix for that too.
 

·
Registered
Joined
·
424 Posts
Sorry, not my business - I guess something wrong with the amplifier? Try the search function, I think it's a common problem.

If you decide to go for a new (used) speedo, I can almost guarantee you, that it will show at least as wrong as your old speedo - they usally show 10% too high.

Anyway, check the backside of your speedo, there must be a sticker or some numbers in the metal like K=xxx or W=XXX. Thats the mesure for the turns, the speedo cable makes per mile. You'll need a speedo with about the same number and since both 240D and 300D (and any gasser model) have different rear axle ratios than Turbos, they will show even more wrong.
 

·
Registered
Joined
·
42 Posts
My speedometer has gotten progressively worse over the last couple of years. My faithful mechanic says it is typical for the vehicle with new speedometers having the same issues. So I just adjust the speed mentally. Now I off about 7mph at around 40 and 15mph around 75 on the freeway. Any suggestions out there as far as reliable replacements or repairing mine?
buy a gps and stop worrying about fixing old junk.
 

·
Registered
1978 280ce euro found dead on Ebay
Joined
·
1,805 Posts
buy a gps and stop worrying about fixing old junk.
Best answer yet, Or you can forget it, I drove for 5 years without a speedometer. Now I have the same as you do I am doing 80 mph on my speedometer but guess I an going only 65 mph, last night I was in a hurry and had car up to 100mph or best guess 80 mph. (that's just keeping up with the other's in the fast lane) The speedometer is off in part because I run low profile 14in tires and in part because they all read wrong to start with. I have been trying to get my wife to follow me somewhere so I can calibrate my car with her car. with cellphones it's not hard, She can go 55 and then I pace with her see what my mph is. then she can 65 pace again 75 etc..

Maybe I will see if anyone I know has a GPS so I can use for a test drive.
 

·
Registered
2013 MINI Copper S Clubman, '84 300CD-weekend car
Joined
·
10,152 Posts
I guess something wrong with the amplifier? Try the search function, I think it's a common problem.
The '84's and '85's took the tach signal from the transmission, vs. the front crank sensor, no amp under hood.
 
1 - 9 of 9 Posts
Top