Can someone supply me with a trouble shooting guide for the cruise control for the 240D/ 1981.
I have vacuum at the acutator, and the fuse checks out good but the system seems to be dead when I attempt to activate it from the selector lever.

Thanks
Howard

Skip troubleshooting for now. Resolder the solder joints in the cruise amp.

Sixto
95 S420
87 300SDL

I will let you know how it works out....btw, is the amp located beneith the dash or is it hidden somewhere else?

Howard

In the W126 it's in the lower part of the dash sort of attached to the steering colum. I don't know where it is in a W123 but I'd check the same place.

Sixto
95 S420
87 300SDL

Hmm... if the cruise control of a 240D has an engine rpm signal even if the car doesn't have a tach then check the archives for the various tricks to revive a lazy tach amp.

Sixto
95 S420
87 300SDL

I don't think your last response about a tach signal was suppose to be sent to me. My 240d does not have a tach...
I won't be able to work on the it till after the 4th....I am working on my 23 Ford Model T roadster so I can be in the 4th parade.....

Again I will post my findings with my C/control...
BTW. My 240 D also drips oil around the rear seal.....Is it realistic to believe I can fix a rear seal leak on an engine that has 275k by just replacing the rear seal?

Be nice......smile...
Howard

The message was for you. I know the name of the part as the 'tach amp.' If the cruise control has an engine rpm signal then there must be a device that counts engine revolutions and translates that count to a signal the cruise amp can use.

Here's what I know of the W126 cruise amp:

pin 1 = red/yellow = +12V in run or start
pin 2 = yellow/green = +12V when cruise switch on decel
pin 3 = gray = +12V when cruise switch not on off
pin 4 = green = +12V when cruise switch on accel
pin 5 = white = singal to cruise actuator release clutch solenoid
pin 6 = blue/red = +12V when cruise switch on resume
pin 7 = black = signal 1 to cruise actuator motor
pin 8 = black/red = +12V when brake pedal depressed
pin 9 = red = cruise actuator feedback reference
pin 10 = blue = signal 2 to cruise acutator motor
pin 11 = green/yellow = vehicle speed sensor
pin 12 = brown = ground
pin 13 = yellow = cruise actuator feedback signal

Okay, you got me. There is no engine rpm signal to the cruise amp because I can't imagine the W123 cruise amp is any different.

If the OM616 is anything like the OM617 then replacing the rear main seal means pulling the crank. But I already got the tach singal wrong so what do I know.

On the other hand a number of these engines have developed leaky oil journal end caps in the back end of the block. I'd call them freeze plugs but you'd probably tell me you're not leaking coolant

So what's more complicated, a 23 Model T or an 81 240D?

Sixto
95 S420
87 300SDL

Thanks for the reply, and I am anxious to get to repairing the cruise. Next week for sure...

I do know that there is a output device on the back of the speedometer that ties in to the cruise circuit, I assume it is a pulse generator that supplies info to the cruise circuit that says this is how fast I am going.....we shall see..

I don't see any provisions for attaching pics to this media, so if You will send me your personal e-mail address, I will send pics of the 23T.

Later
Howard
goodwinds@cox.net

Almost thru with Hot Rodding the 23t. Then I can get serious on the cruise delima.
I did however, drop the cruise amp.( located just above the drivers ankles on the inside of the lower dash panel), resoldered the plug contacts, (which looked just fine before I touched them up). The result was negative.

I found a 300d station wagon, automatic in a friends salvage yard. I pinched the cruise motor/actuator since it was the same as the 240d and will slip that on just for grin and giggles and will report the results.

Hot here in North Carolina just now, and I hate sweating......smile..

Howard

any luck on fixing your cruise? mine does work, just fairly jerky, or at certain speeds it only wants to go faster.... maybe the speed sensor is the culprit. all advice will be greatly appreceiated,if not actually put to use

__________________
1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.