Cruise control problem - 1978 450SL

Hi. Can anyone advise on how to troubleshoot this problem? Cruise Control lever accelerates when lifted and decelerates when dropped. It does not stick to any speed.
I don't know what components make up the cruise control, especially when we talk about 30 year old technology.
Your suggestions will be really appreciated.
Tks... Angelo
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That indicates that the servo is operational as well as at least part of thw switches on the the control stick. The other components are the cruise control amplifier and a speed pickup, which is probably located on the speedometer in that model. Of these, it's usually the cruise control amplifier which is kaput. The Germans aren't very good at electronics. You can try removing the amp, opening it up, and resoldering the solder joints. I've seen it claimed that most failures are the result of cold solder joints working loose. But with personal experience, I've never gotten lucky trying that approach.
They should be available as rebuilt ones from parts places for about $180. Also, I think General Development Labs either rebuilds your own or offers rebuilt exchanges. Not sure where it's located on that car. On my 1980 300SD, it's mounted under the dash, in the parking brake/regular brake pedal area. It's an aluminum rectangular box, maybe 6"X4"X1"
It does not stick to any speed.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Rebuilder: http://gdl-online.com/begin.html
--

2008 T.G.Lambach. Publication in any form requires prior written
permission.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.