Author Topic: CSS $1 fix for a $1000 part  (Read 532 times)

Roman Kishi

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CSS $1 fix for a $1000 part
« on: June 02, 2019, 21:38:08 »
My CSS has been malfunctioning for a long time. It gets stuck in the outward position and preventing the idle speed from going down to normal RPM once out of gear.
A new one is marked for 1000 Euro at SLS site and it's not even available . I had a simple cheep solution using 3 small tension springs between the tip of the rod and the 3 screws at the base, thus forcing the rod to retract once the CSS is inactivated. It worked great and cost me less than $1. Its temporary fix but I think will last for few years until the guys  in Stuttgart decide to manufacture the part again.
Roman
Northern Virginia
280 1969,Signal Red,Parchment Leather, Auto, A/C

Rolf-Dieter

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Re: CSS $1 fix for a $1000 part
« Reply #1 on: June 02, 2019, 21:53:44 »
I call it great reverse engineering, well done!

Tip, do carry a few spare springs in your glove box :)

Dieter
Dieter

Mercedes-Benz 1969 Pagoda 280 SL Auto. Exterior Blue, Interior Blue Leather
Mercedes-Benz 2011 SL 63 AMG Roadster, Exterior Sliver Metallic, Interior Black Leather
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Pawel66

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Re: CSS $1 fix for a $1000 part
« Reply #2 on: June 03, 2019, 04:29:52 »
I had an issue of linkage not retracting fully to "zero" as CSS was holding it in the last movement phase. I bought both of the return linkage springs from several sources to try to find the spring force  strong enough to retract linkage all the way. When I found it, it turned out that CSS at times does not have enough power to push the linkage. So now I am back at a little weaker return spring at the throttle - we will see.

By the way - when Daimler or if Daimler start supplying CSS again, you may miss the USD 1k price...
Pawel

280SL 1970 automatic 180G Silver
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awolff280sl

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Re: CSS $1 fix for a $1000 part
« Reply #3 on: June 03, 2019, 11:12:03 »
I had similar problems with my CSS which is for the AC (manual transmission).
When I decreased the spring tension on the throttle linkage, the CSS would not fully retract. When I increased the tension, the RPMS would not bump up.
I hooked up a dedicated relay for the CSS, adjusted the spring tension to the best position, and it fixed the problem. It seems that the power wire to the AC compressor was not supplying enough power to the CSS when shared with the AC compressor.
I don't know if this is applicable for a CSS used in the automatic transmission situation.
Andy   Sarasota, FL
'69 280SL 4speed
'06 Mitsubishi Evo

Pawel66

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Re: CSS $1 fix for a $1000 part
« Reply #4 on: June 04, 2019, 08:27:36 »
Andy, thank you for a very creative suggestion!

I was thinking last weekend about how to, perhaps, give the CSS a bit more "food". Contacts are clean. I have 12.4V on CSS when engaged, seems enough, but... What if I sourced power to CSS from a "clean place" through the relay? This is what I read for me from your post. Hydraulic switch would turn the relay on by giving it ground, and relay would give power to CSS.

Hooking a CSS for transmission electrically through the back up/starter firewall switch does not work well as the signal you get to CSS comes too soon and CSS kicks off before the gear is engaged causing: rev up then gear in. You can use it as emergency when your transmission switches are gone.
Pawel

280SL 1970 automatic 180G Silver
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W121 190SL
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lpeterssen

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Re: CSS $1 fix for a $1000 part
« Reply #5 on: June 06, 2019, 20:53:48 »
Dear friends

The CSS constant speed solenoid on Automatic transmission cars engages (activates) only when two conditions are met at the same time:

1) idle switch at intake manifold is active (when at intake butterfly is fully clossed)

2) and the low pressure switch at the automatic transmission is clossed

When those two conditions are met at the same time then a relay feeds power to CSS

Study the wiring diagram that is posted on the pagoda forum

That is my contribution for the topic

Regards
Lp

Pawel66

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Re: CSS $1 fix for a $1000 part
« Reply #6 on: June 07, 2019, 05:46:57 »
Well, not really always like that...

At least in the set up without emission control and without AC, CSS is powered from fuse No. 5 permanently when ignition is on and gets ground from pressure switches on the automatic gear box when any gear is engaged. Throttle switch gets power from fuse No. 3 and when closed provides it to the 3 position solenoid. There is no relay anywhere. There is no direct electrical connection.

CSS is engaged permanently when you drive. Disengages only when you move the gear selector to N or P.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

lpeterssen

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Re: CSS $1 fix for a $1000 part
« Reply #7 on: June 07, 2019, 12:01:51 »
Dear Pawel

Thanks for your comment but I think we require further analysis to come to a conclusion together.

I agree that on automatic cars fuse no.5 feeds the positive lead on the CSS all the time as long as car is on ACC on position.

The negative lead as far as I saw in one diagram but I don not remember which one it was,  comes from as you said the low pressure switch on the automatic transmission which passes first trough the throttle switch (which closes the circuit only when throttle butterfly is clossed) and then feeds the negative lead on the CSS.  From that I understand that it means that the negative lead will activate the CSS only when the two conditions are met: low pressure switch on automatic transmission says the pressure is low and when the throttle switch says the butterfly is clossed.

So I think that low pressure switch activation can only happen when car is still on a traffic light for example with the gear selector on the “D” or any other gear and driver is not accelerating the car with the pedal.  Mercedes just to be on the safe side added the conditional that only if throttle was on the closed position then activate the CSS. Why? I do not know, because I can not think into a situation on which the low pressure swicth from auto transmission is activated when the car is not still iddling.

Waiting for your comments and please refresh my mind on which drawing diagram appears what you and I are describing since I can not find it.

Regards
Lpeterssen
« Last Edit: June 07, 2019, 16:49:24 by 66andBlue »