Cruise Control on '79 W123 - PeachParts Mercedes-Benz Forum

HaloArchive · #1 11-09-2012, 06:34 PM

Hello All,

I have a 1979 w123 240D Auto and was wondering how to even use the cruise control? I can't test if it is working if I dont know how to use it

Thanks!
H

charmalu · #2 11-10-2012, 09:49 AM

welcome to the forum

The cruise control lever has 4 setting.
1. lift up, setting (touch switch) Accelerating (hold switch)

2. push down, Setting (touch switch) decelerating (hold switch)

3. push away from you. Cancelling

4. pull toward you. Resume.

Hope this help some.

Charlie

toomany MBZ · #3 11-10-2012, 10:21 AM

From the owners manual.

HaloArchive · #4 11-13-2012, 05:27 PM

Thank you both for those links/instructions!

HaloArchive · #5 11-13-2012, 05:28 PM

Quote:

Originally Posted by charmalu

welcome to the forum

The cruise control lever has 4 setting.
1. lift up, setting (touch switch) Accelerating (hold switch)

2. push down, Setting (touch switch) decelerating (hold switch)

3. push away from you. Cancelling

4. pull toward you. Resume.

Hope this help some.

Charlie

So, to set it, I hold it up? Or, do I hold it towards me?

jay_bob · #6 11-13-2012, 07:28 PM

Either up or down works for the initial setting.

Once you are set, then pushing down decreases the set point and pushing up increases the set point.

Pulling towards you re-establishes the set point, if you tapped the brakes (or clutch) without having turned off the car. If you were set at 70 and you are now doing 50 it will accelerate to the set point and hold.

Pushing away turns off the system.

HaloArchive · #7 11-13-2012, 07:42 PM

Quote:

Originally Posted by jay_bob

Either up or down works for the initial setting.

Once you are set, then pushing down decreases the set point and pushing up increases the set point.

Pulling towards you re-establishes the set point, if you tapped the brakes (or clutch) without having turned off the car. If you were set at 70 and you are now doing 50 it will accelerate to the set point and hold.

Pushing away turns off the system.

Thanks Jay,

I tired it out and it did not work. The vacuum line to it is not leaking so it must be something else?

jay_bob · #8 11-13-2012, 08:07 PM

You have an amplifier box under the dash, a vacuum pod under the hood that tugs on the throttle, and a speed sensor on the back of the speedometer head in the cluster.

Any of those could be the cause.

I know JamesDean is the resident CC expert.

However from what I have read is that the best fix for one of these old vacuum systems is to replace it with a modern aftermarket control system. Check the wiki, someone even figured out how to reuse the existing stalk switch so that it is transparent to the user.

Alastair · #9 11-13-2012, 08:32 PM

First, Check the cable to the actuator. This causes most of the mechanical issues with this type system.
The cable often frays at one end or the other and jams up in the outer part.
It can be easily removed from the actuator by removal of the screws and unhooking the cable
The cable should have approx 1mm free-play when the throttle is closed.

There are two pipes to the actuator. One is Vac supply and the other leads into the cabin and is the air-source--just make sure its not blocked--goes into cabin as it was assumed this is a clean source of air.

The cable can be replaced by using the inner from a push-bike brake-cable.

The actuator is pretty reliable although the diaphragm can perish--You'll see that when you remove the cable....

The main electronic faults relate to dry soldered joints and some caps in the controller.
This is fitted behind the kick-panel on the side in front of the driver's side door.
Its a ally tin-can approx 6" by 4" secured by a bracket. After removal from car and unplugging the leads, It can be opened up after unlocking the bent-over case, the PCB will then slide out attached to the elect socket.

There are a couple of electrolytic caps (47uF 25V) that will need replacing--Use a modern 63V type at 47uF.

HaloArchive · #10 11-14-2012, 04:47 PM

Quote:

Originally Posted by Alastair

First, Check the cable to the actuator. This causes most of the mechanical issues with this type system.
The cable often frays at one end or the other and jams up in the outer part.
It can be easily removed from the actuator by removal of the screws and unhooking the cable
The cable should have approx 1mm free-play when the throttle is closed.

There are two pipes to the actuator. One is Vac supply and the other leads into the cabin and is the air-source--just make sure its not blocked--goes into cabin as it was assumed this is a clean source of air.

The cable can be replaced by using the inner from a push-bike brake-cable.

The actuator is pretty reliable although the diaphragm can perish--You'll see that when you remove the cable....

The main electronic faults relate to dry soldered joints and some caps in the controller.
This is fitted behind the kick-panel on the side in front of the driver's side door.
Its a ally tin-can approx 6" by 4" secured by a bracket. After removal from car and unplugging the leads, It can be opened up after unlocking the bent-over case, the PCB will then slide out attached to the elect socket.

There are a couple of electrolytic caps (47uF 25V) that will need replacing--Use a modern 63V type at 47uF.

Okay, so pulled the actuator mechanism out of the car and it is working properly and the diaphragm is in working order. Do you have a picture of the electronics tin can? I cant seem to identify it.

Thanks

EDIT:

Okay so I think there MAY be something up with the diaphragm. How the hell do I get it out of the actuator?

HaloArchive · #11 11-14-2012, 06:11 PM

I have uploaded a picture of the PCB. Which two caps need to be replaced?

jay_bob · #12 11-14-2012, 06:21 PM

The two things that look like silver cans with a + and - on them.

Be sure to note the orientation of the + and - the caps are polarity sensitive. New caps may be marked differently but just be sure to match polarity however it is marked.

New caps of the same uF rating and equal or greater voltage will work. Greater voltage is acceptable but less is not. These are known as "radial" lead capacitors.

Try mouser.com or digi-key.com for the parts. You might get lucky at radio shack but nowadays they seem to be more interested in cell phones and rc toys than serious electronics.