Hello! My 1982 240D cruise control does not work. What are the top issues that I should address? Are these somewhat simple to do? Is there a diagnostic to see what the real issue is? I am ready to take my 240D across country but the buzzing from the gas pedal makes my foot tingle (the bad way!) after about 20 minutes. Any info would be helpful. Thanks.

 

I have driven 300Ds for 28 years (time flies...) and only twice had cruise control problems. They were both easy to fix. Check for vacuum leaks around the C. C. components. Anything from a cracked vacuum line "t" to a leaking hose. A hand vacuum pump with gauge is a great tool for a MB owner.

 

1982 240D cruise is all electronic - no vacuum. The cruise amplifier (located driver's side under dash on left near fusebox) can get funky with age and begin to perform erratically. You can usually get one cheap at a junkyard and take a chance it may solveyour problem. If you know a little about electronics you can take yours apart and check for bad solder connections on the circuit board and repair them. A rebuiltunit costs about $250.



The cruise servo (engine bay) unit's internal contacts wear with age because the servo is directly connected to the throttle linkage, so every time you depress/release the accelerator the servo's contact brushes wear away at thecontact points on the servo's internal circuit board. This sends a weak (or no) signal back to the cruise amplifier and in turn the system can't properly control the throttlebecause it has no idea of the current throttle position. Rebuilt servos can be had but they are expensive @ $325.00.

 

Dirty D - thanks for the info... I'll start with the amp and go from there. Appreciate the tip.
[8D]

 

RE: What is most common cruise control problem?
The cruise amplifier can get funky with age and begin to perform erratically.
The brake lights may work, but corroded contacts will not provide a positive ground path for the cruise unit to see.
These might be reasons why my '87 300D Turbo (241,000 miles) cruise control is working perfectly on some days, which are becoming fewer and fewer, and then not work at all. I replaced the servo, it made no difference. I took the amplifier appart and everything looked ok. Put it back in and everything remained as before. Since the cruise control is totally unpredictable when it will work and when not, a weak ground may be the answer. What about a capacitor or diode inside the cruise amplifier eing faulty? Who can bench test a cruise control amplifier?

 

This link should have all the diagnostic information you need.
roy@pelicanparts.com


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