Need cruise control help please!

[RG5384]

This is only the second to last thing that my 83 300SD needs to have EVERYTHING working, and the thing i've dreaded most fixing. The cruise control on my car is completely inoperative. It won't acclerate only or anything, it's like the switch isn't even plugged in. I've taken the amp out and re-soldered everything, with absolutely no effect from it. The tail lights are working properly. The previous owner had told me that before it completely went out it would take a while to completely kick in, but once it did it worked fine until it was turned off. I'm basically looking for info on how to troubleshoot this complex system, and also, what vacuum component runs this system? i know the vacuum system has something to do with it, but i dont' know where the sensor is etc, so any info on that is also appreciated. Thanks!
Ryan

[engatwork]

Check out this site -

www.gdl-online.com

Call Peter at the number listed. He does a real good job with the cruise control systems.

The first thing you can do yourself is to make sure all of the linkage is cleaned and lubed.

[RG5384]

thanks, what linkage though? the regular throttle linkage? keep in mind i have absolutely NO CLUE about the wear abouts of the sensors etc under the hood. The only two parts that i know where they are is the switch(duh) and the amplifier. What part of the system tells the cruise where to hold speed etc? Also, if i have him rebuild me one i will have to go buy a salvaged one b/c mine has already been taken apart and mutilated!
thanks
RYan

[engatwork]

Ryan - I am referring to the mechanical linkage that ties the throttle system to the cruise control. The cruise control is the item between where you check/fill the power steering fluid and the valve cover. There should be a "linkage" between this and the throttle linkage. While looking under the hood have someone mash the gas pedal a few times - the parts that are moving are the "linkage". These "pivot" ball ends of these items are supposed to be occasionally cleaned and lubed. I used to use ATF for lube but now use Marvel Mystery Oil. I feel certain that the linkage is not your problem though. Call Peter at the 800 number on the site and discuss it with him. He is good people to work with.
The cc amplifier (on a 300D anyway) is underneath drivers side dash between the steering column and the door.

[RG5384]

ok thanks, i found what you are talking about. That giant servo looking thing is the actuator right? I knew where the amp was, and i've already tried re-soldering everything in it etc. My only reservation about calling peter is that i have no intention on spending the kind of money on rebuilt parts that it would take. I would try to rebuild the broken parts myself first. Also, on a 300SD(w126) which part of the system has anything to do with the vacuum system? thanks a ton,
Ryan

[engatwork]

I don't know if your car's cc has anything to do with the vacuum system or not? I know that my 300D cc is not tied into the vacuum system. Anyway, my guess is that you will need to replace the "electronic" part of your cc (the part located underneath the drivers side dash). You are probably looking at couple hundred bucks (US). If I were you I would at least call Peter and discuss the options.
good luck

[RG5384]

ok thanks for your help, as always it's greatly appreciated!
Ryan

[psfred]

Ryan:

Cruise control is electrical -- amplifier drives a servo motor (reversable). The gld site has some good instructions.

Both the servo and the amp can go bad -- if the servo get stuck it will fry the amp -- seems MB hasn't learned about current limiting circuits yet.

It is possible that the servo is dirty and can be cleaned, but you will have to test it. Make sure it is working properly, as a shorted one will fry not only the amp, but the MB test equipment, too!

And don't forget to do the electical checks on the switch, too -- the one in the TE is "floppy", and I'm sure that is why the CC doesn't work -- won't stay engaged (amp is probably bad, too, but for sure the switch).

Peter

[RG5384]

thanks psfred, i did look at the site and i think i'll do some troubleshooting with it on tuesday. My other thought is just to buy an aftermarket cruise system and rig it up to my existing switch. I can get an entire system for under 100 bucks that way, and no one would ever know the wiser. Any recomendations on this route? Is it even possible on this car without a computer speed sensor wire? thanks again
Ryan

[psfred]

ryan:

Wouldn't go that route -- far too much trouble when you can replace the servo or amp and drive for who knows how long with a system that holds the speed within half a mph instead of wandering all other the place.

Check your fuses, too, just in case!

I know that replacement parts for the MB system seem expensive, but the gld prices are not bad, and you won't have to hack into the wiring, find and cut the speedo cable, etc like you would for an aftermarket, so say nothing of the fact that the aftermarket ones I've seen aren't too robust looking.

After all, there is always the junkyard route to save money! The U-pull-it types are best -- much cheaper!

Peter

[RG5384]

yea i guess your right. But spending over 300 bucks on crusie control just seems like such a waste to me. I'll look into used but hardly any of these cars have working systems on them anymore, so am i just playing with fire with that? thanks,
Ryan

[Blair Mahaffey]

Ryan,

I had the same problem with my 83 300D. I looked up front in the engine compartment and it appeared everything was okay.

I searched all the threads on this forum, first.

I took out the amp and tried to resolder, but to no avail. I finally ordered a rebuilt amp from "The Benz Store" in Atlanta. $145.00 with a three year warranty.

It was delivered to my office. I went outside, plugged it in and boom, Cruise Control. Sometimes the amp is beyond repair by simply soldering. But a rebuilt for $145.00 is a deal.

When my father's 190's cruise went out, I replaced it with a rebuilt and it is working fine now also.

Blair

[RG5384]

thanks for all the help guys, i think i have decided to check the actuator using the method described at GDL, and check the swithc. If both those check out i'll get the amp fixed, if they dont' i'm going to go with the JC whitney cruise system. Thanks for all the help again,
Ryan

[RG5384]

i thoght i would update you all on my progress so far. I tested the switch tonight, and it works fine, i also tested the actuator. I coud hear the motor run, and it was drawing b/w 145-147 ma, well within the allowable range. I then tested the cilinoid and heard it click in. Just to be posotive i didn't have any broken gears i dismantled the actuator, and it all seems to be pretty solid in there still. My next step is to try to figure out how to get out my old amp when it has a stripped out 11mm socket and in-accessable philips screws. Can we say dremel???j/k Once i get the amp out i'm going to go to a salvage yard and just try one amp after another till one works, and i should have a working, FACTORY cruise system. thanks for the tips everyone, i'd be installing an el-cheapo cruise system if it werent for you all! thanks again,
Ryan

[RG5384]

just thought i'd tell you all that my cruise now works, i pulled a used amp out of a 91 W126 and that did the trick. I paid 125$ for it, i would have contacted that place in Atlanta but i wanted the cruise to work on the way to atlanta for thanksgiving. Thanks again for all your help. I think i'm just going to zip tie the new amp to the shell of the old one, there appears to be plenty of space under there,and i still can't figure out a way to get my old one out! thanks again everyone!
Ryan