W123 cruise control actuator - PeachParts Mercedes-Benz Forum

Guest987 · #1 03-07-2014, 04:36 PM

Was testing cruise control today. Started with the actuator. Test for motor in normal position I hear the motor run, as well as, in the reverse position. What doesn't happen is the actuator arm does not move? Any idea what is the reason or what might be the issue.

jay_bob · #2 03-07-2014, 05:30 PM

Actuator check out

You need a multimeter, a 12 V drill battery, and some clip leads.
Feedback pot:
- Check pins 1-3, should have about 3.5 k ohms (3500 ohms) always
- Check pins 1-2, should go from 3.5 k ohms to zero as you rotate the shaft
- Check pins 2-3, should go from zero to 3.5 k ohms as you rotate the shaft
I cannot remember which way is which, but it should go one way from 1-2 and the other way from 2-3.
Motor:
Check pins 4-5, should have a few ohms resistance
Jump drill battery power to pins 4-5, the motor should whir. Put your meter on amps, in series with the battery and the motor, make sure you are under 200 mA (or 0.2 A).
Solenoid:
Check pins 6-7, should have a few ohms
Jump battery power to pins 6-7, you should hear solenoid click.
Do not jump 4-5 and 6-7 to power at the same time or you will damage the gear train

JamesDean · #3 03-07-2014, 06:49 PM

The motor and arm are only connected when the solenoid is engaged (pins 6-7 as jay_bob indicated)

Some additional information.

The feedback pot varies depending on model. The older 001 series is 3 to 3.5K The newer series (cant recall part number) is around 2.4K

If your motor draws more than 200. Its possible that you can get this down by cleaning the commutator and brushes. I did this on one customer's actuator. It was drawing >250. I opened up the back end and found lots of stuff all over the commutator and motor windings. I cleaned this all up with some brushes and IPA and it fell back down to around 180 mA.

I've been considering offering a cleaning and lubrication service for a small fee, say $30? . I do offer free testing.

Here are some internal photos:
VDO Cruise Control Actuator - Imgur

Inside The Box - VDO Cruise Control Actuator - Imgur

I recently had a chance to play with a few actuators. I found that the older models have--what I would consider--a defect. The older actuators will keep trying to drive the gears even after the arm had reached its end of travel. This results in high current draw and gears jumping. The newer models don't do this.

Nominal current draw is somewhere below 200mA. When the actuator was hitting its end of travel point and not stopping I saw current draw jump to 1.2A.

I did notice that the potentiometer on the older unit is roughly 3K ohm total. And the newer ones are 2.4K or so.

The "older" units carry a 001 545 75 32 part number.

The "newer" unit carry a 002 or 003 series part number I can't remember at the moment.

Guest987 · #4 03-10-2014, 03:45 PM

Well, I stopped the testing on the actuator, because I knew from external reasons it was good. I spent time cleaning the harness connector real good, because from moisture they can get corroided from dampness. I used a connector grease and sealant putting back together. I moved to testing the amplifier connector. Everything was going my way until I got the pin #8, where I went open. I knew it wasn't the brake switch, because of what I noticed on the garage door toggling the switch. I bridged the clutch and I got power to the #8 terminal. This was the bad part. The good part is I wouln't have found the part I needed, if it wasn't for WHunter settling a dispute quite some time ago in a thread I ran across. He just posted a part number for a reply. I had checked several places to no avail on finding the item by description, until I retreived the number he posted. I continue to get the response, that these oldies are not listed out there anymore. Anyway my thanks for the help, and WHunter's info!

Guest987 · #5 03-10-2014, 09:41 PM

When I worked on the 190 2.6's, I found that Mercedes knew how to design them tight. Well, working under the dash on the manual 123. I found out, that they knew how to stuff 'em on those manual's, as well. That pedal assembly with the switches and clutch cylinder is really sandwiched in there, I think.

Guest987 · #6 03-20-2014, 02:25 PM

Well, got my new switch the other day, and installed it today. I went for a test run to see if the CC would now work. Surprise, surprise it worked really good. It is nice and smooth, and will kick-in at around 30 mph. The amplifier is definitely a keeper. If you need any work testing or rebuilding on the cruise control equipment James Dean is the one to see. He does a great job and is thorough and very reasonable!

JamesDean · #7 03-20-2014, 03:11 PM

Thanks Rebe! Always glad I could help! Glad you got it working and are pleased with it!