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New guy working on a 1971 280 SEL Speedometer

3K views 7 replies 6 participants last post by  drew56cus 
#1 ·
Hello Benz World,
I'm a new guy here trying to learn more about older Mercedes. I'm a personal mechanic for a gentleman who has a little collection and it's my job to keep them running. I do have a very tough time finding information about them so I hope you fellas can teach me some things.
The first car I have in the shop now is a 1971 280 SEL. Today I've been trying to figure out why the speedometer isn't working. I climbed under the car and couldn't see a speedometer cable but did see a cylinder on the passenger side of the transmission oil pan, is this the speedo mechanism? There is a green wire right there coming out of the floor that has been disconnected from it. There is a red wire that is connected to it now that someone had added, and zip tied up around the firewall down to a mysterious two-wire switch/mechanism near the steering gearbox. I'm trying to be very delicate with this car, do you fellas have any advise?
I appreciate your help
-Wes
 
#5 ·
Removing the speedo cluster is fairly easy with small hands....

you have to reach up under the dash and find 1 or 2 plastic round knobs that are about 1.25" diameter, located on the backside of the cluster. all you have to do is unscrew them by hand, then you can pull the entire cluster forward, disconnecting the oil pressure line and other wires. the temp guage is mechanical so you have to be careful there also, I think you need to remove the guage from the back of cluster since the mechanical tube goes forward to the engine.

remember not to start the engine with the oil gauge undone or you will squirt oil at you.


removal of gauge cluster on w108 - PeachParts Mercedes ShopForum
 
#6 ·
Thank you for the great replies they were really helpful. I removed the bottom dash panels and is just too tight to get my hands up there to remove the cluster without taking parts off. The speedo cable seems to be intact from the outside. Would you think the chances are the inoperative speedo is most likely the speedometer gauge itself?
Thanks again!
-Wes
 
#8 ·
Speedo cables often have the inner drive snap somewhere. If you got the back off the speedo gauge and bought it into the footwell so you could see it, and had the back end up in the air, you could put the trans in drive and get a mate to turn the prop shaft. If the inner part of the speedo cable does not rotate then you have found your problem. I have normally found speedo's start jumping around erratically before dying, so if it did not do that, my bet would be on the cable.
Any instrument repair shop should be able to make up a new core for you if you give them the ends, or try wreckers or the friendly (more local) folks on forums such as this for a used one.
Cheers, Drew
 
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