Constant Speed Solenoid Always Engaged

[Rolf]

I have perused the threads pertaining to the CSS and found alot dealing with it not working. My extends all of the time. As soon as I start the car the rod extends outward. Could the switches on the transmission be the culprit? Also, I am not able to adjust it at all. It seems to be frozen on the shaft. I tried to turn the nut while holding the shaft with a small screwdriver without any success. I soaked the threads with oil and even (ouch) tried to turn it using a pair of small vise grips on the shaft, no luck. I do not know if the nut and the knurled wheel on it are separate or one piece. Also is the shaft spring loaded somehow? The shaft slides in and out from the solenoid without resistance of any kind. I have a  1966 230SL.



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[J. Huber]

Hi Rolf. I am not sure I can help much. I do notice your adjustment nut and stopper disc (?) are way farther down the shaft than mine. In my case, the disc is almost to the end on the screw. I realize you can't seem to move it -- just an observation. Good luck.

PS I think the nut and disc are one.

[tuultyme]

I had he same problem as you when I got my car.  One of the wires from the CSS runs to the left transmission (automatic)pressure switch; from that switch another wire runs over the transmission to the right transmission switch.  These switch complete the grounding of the CSS causing it to activate.  On mine the wire going over the transmission was grounding itself somewhere.  I added another wire to replace the original wire which I could not pull out.  Anyway now my CSS works properly.

[J. Huber]

Rolf. I just looked at mine. The nut & disc on mine are one but there is a second "lock" nut that tightens up next to it. On your picture, it almost appears that the disc and nut are separate...

Also,for what its worth my inside most wire to the CSS is brown and green striped. the other appears black.

[Rolf]

Forgive my ignorance, I know somewhere in this forum it says where the transmission pressure switches are but I can't find the thread. Can the switches go bad and keep the solenoid active?

[glennard]

There's a 2 position solenoid on top of the auto tranny, pressure s/wes on each side of the tranny.  The kickdown and butterfly s/wes tie in to this circuitry.  We need a definitive explanation of how this all works- - i.e. give it gas, butterfly s/w activates the ---??, which does what to tranny?, etc?  Stomp on the accelerator pedal, kickdown s/w activates , tranny does what??, etc

[Rolf]

As soon as the car starts, the css is activated. It doesn't matter if the car is in gear or not. If I electrically disconnect the CSS the rod can be moved by hand. I do have kickdown up to 30 mph.

[Cees Klumper]

Hello Rolf - your wiring must be faulty, as Bruce suggested. Either one or more wires is/are misconnected or, as you speculate, one of the two pressure switches (one located at the left and one at the right lower side of the automatic transmission) could perhaps be stuck in the 'activated' position.

There is a link in one of the threads on the CSS to a Mercedes Dismantler's file that tells you how the wiring to the 3-position solenoid should be connected that may help. It's correct that, with the circuit completed by one of the two switches, the solenoid is activated.

In fact, as you drive the car, the solenoid is continuously activated, meaning the electro-magnet is constantly 'alive' even though, when the car is moving more than a few MPH, it is redundant.

With the power off, the shaft should be movable freely as yours does, no spring-loading or resistance. You definitely want to fix this issue, because it will make driving the car (having it maintain a steady idle putting it from neutral into either reverse or drive) much more pleasurable. See also my earlier posts on this topic, I finally resolved (I hope, fingers crossed) an intermittently malfunctioning switch by having it simply replaced with a new one.

Also got a new CSS, 'just in case' - I figured after some 40 years of constant-activation-while-driving the original one earned its retirement!

[graphic66]

Your constant speed solenoid is only controlled by the two switches on the transmission, nothing else. Positive power is supplied unswitched from fuse #5 directly to the solenoid and is always supplied power while the ignition is on. The negative feed for your CSS is switched at the transmission by the two hydraulic switches located on the lower right and left front of the transmission. If yours is always on then somewhere the wire from the transmission switches to the CSS is grounded. I would first unhook both switches, if it is still on you have a short in the wire going from the switches to the CSS or someone rewired it wrong. If the switch turns off when you unhook the switches, hook them back up one at a time and see if it comes on, this should determine if a switch is internally shorted.This is a very very simple circuit, one wire from fuse 5 to the CSS to provide + power and one wire from the two switches on the transmission to provide switched - power when the transmission is shifted into a gear.. The throttle body switch has nothing to do with this circuit at all. The throttle body switch only runs the double acting solenoid on top of the transmission and should open immediately when the throttle is opened and engine has reached 1600 RPM max. The transmission wiring is a very simple circuit with 4 switches and two solenoids.

[glennard]

Still looking for how all this stuff is S'posed to work and the total, complete wiring diagram.  (Not 'dismantlers' partial).  Please describe in understandable fashion how the accelerator pedal, CSS, throttle S/W, tranny s/wes, tranny solenoid, kickdown s/w, etc work together in 'perfect harmony'.  Also, the wiring and hydraulic diagram to support this.

[graphic66]

The only thing missing at the http://www.mercedesdismantlers.com/16BoltInstallationInstructions.html site is the positive + feed for the idling switch on the throttle body bringing power from fuse # 3. Other than that it is complete and accurate. The only thing the CSS does is increase the idle speed when the car is in gear by switching the ground wire to the CSS using hydraulic pressure in the transmission. I'm not sure why the switch on the firewall wasn't used to do this.
  The idle switch activates the double acting solenoid on top of the transmission. At idle the linkage from the double acting solenoid should be moved to the rear, at partial throttle the idle switch opens and it moves the double  acting solenoid to the central position, and at full throttle with the kick down switch activated it should move forward.
  The double acting solenoid can be tested with the car not running. Turn the ignition on, watch the solenoid while someone pushes the gas pedal and watch the linkage under the car.  
  The CSS can only be tested with the car running. In neutral the negative feed to the CSS should not be grounded, in forward or reverse it should be grounded. This test can be made by using a test light on the CSS terminals, in gear running, the light should light, in neutral, no power.
  So, as you see a very simple electrical system and very easy to test. 3 switches and two solenoids feed by two fuses.

[wwheeler]

David,

Thank you for your explanation of the two control systems. I do believe I understand it now.

So, the two transmission switches (one for reverse and one for drive) only purpose is the activate the CSS. And the CSS is always activated in reverse or drive gear no matter what speed or throttle setting. Sound right so far? With an a/c system, the CSS is also activated by the compressor clutch. How does that work into this system?

Thanks for the education!

[glennard]

WW, Thanx- the A/C ties in also.

[graphic66]

I haven't seen an example of how the AC is wired. If I were to wire it I would use a relay wired to the AC clutch that would switch the CSS on by grounding the wire that goes to the tranny switches. This would only change the idle in nuetral and it would be the same in gear as it would just activate the CSS when you turned on the AC. As the CSS has only two positions you can't make it idle higher when the AC is on and the car is in gear. I have tried to think of how you could make another solenoid to push a little farther when activated by the AC, but I can't come up with anything. My car just idles a little lower with the AC and runs fine. I also don't use it that much. It really works acceptable though. To wire the relay see http://www.6066gmcguy.org/BoschRelay.htm  . You would wire a ground to #85 and #30, the hot wire to the AC clutch to #86, and the grounded side of the CSS that goes to the tranny switches to #87, you wouldn't need #87a terminal. This is just an educated guess on how to do this, not an experienced one. If anyone has a better idea please help us out. But you will still idle the same if the car is in gear, again, this only helps your idle in nuetral with the ac on and hardly seems worth the effort and mess to do this retrofit.

[Cees Klumper]

quote:Originally posted by graphic66

The only thing the CSS does is increase the idle speed when the car is in gear by switching the ground wire to the CSS using hydraulic pressure in the transmission. I'm not sure why the switch on the firewall wasn't used to do this.

That would not work since the microswitch is only activated when you press the accelerator pedal; i.e. when you put the car in either forward or reverse gear without pressing the accelerator, the switch is not activated and so would not activate the CSS.

However, now come to think of it, that switch could be put to good use by ... additionally wiring it into the CSS circuit by making it interrupt the power to the CSS when the accelerator is depressed (on my microswitch there are actually two connections: one that is 'off' when the switch is activated, and one that is 'on'). That way, the CSS would activate as normal when the car is put in gear but the accellerator pedal is not pressed, and then when you do press the accellerator to drive off, the CSS (which is then no longer required to maintain idle speed), would be de-activated rather than staying in 'energized' mode all the time as is now the case. Think I will try that out next time I see my Pagoda (am in France now on vacation). Imagine this thread leading to a slight improvement over what the Mercedes engineers came up with 40 or so years ago!

[hands_aus]

I wonder what they did on the sedans of the same era with air conditioning.

[glennard]

Cees, Welcome to 'Shade Tree Institute of Pagoda Engineering'. -- Graduate degree in MB upgrades.  By the way we haven't figured out how the old stuff works yet.

[glennard]

Make that 'International Institute'.

[Rolf]

Thank you all for the replies. As soon as I can, I'll check the wiring and hopefully find out what is wrong. As to the adjustment, I can't seem to move it either up or down the threaded shaft. I have tried holding the disk and turning the nut but the shaft rotates along with the nut. I tried a screwdriver in the slot at the end of the shaft and it seems the nut is frozen on the shaft? Any suggestions?

[glennard]

How about a little heat? -very little.

[Rolf]

Thank you all again for your suggestions. I plan on getting back to the car in a while. Right now everything is on hold as my family is going through a sorrowful time. My son passed last Saturday. It may be a while before I get back to reality and continue with the problem. I'll let you know of the results when I do.

  Thank You All

[J. Huber]

Help! I recently disconnected the two wires on the top of the CSS for removal. (automatic obviously). Now I lost track of which side goes where!  Can anybody save me again... I tried searching for it but came up empty.

[Naj ✝︎]

Hope this helps

naj

[J. Huber]

It sure does. Thanks Naj. I had recited ..."green on the left, green on the left...." -- just forgot whose left