Constant Speed Solenoid ? HELP!

[abe280SL]

New to forum....great place.  I have a 68 280sl and my constant speed solenoid the lies over the intake manifold on a bracket (the one that pushes out when the transmission engages forward/back or a/c if you have a/c..i dont) works in reverse but it does nothing in forward.  Where should I look to find the problem?
thank you in advance,
abe

abe
1968 280SL Auto
Signal Red w Beige Int

[J. Huber]

Hey Abe. I find it a little strange that it is working one way and not the other. First off, you probably know the CSS can be adjusted? You might also want to check your linkage measurements to be sure it is adjusted correctly. You may find that with the linkage just right, the car takes the in gear shift better and meets the CSS as it extends. Good luck!

James
63 230SL

[abe280SL]

James, as I mentioned the solenoid engages in reverse but not drive.
I put the car in reverse, I go under the hood, and the solenoid is firmly pushing out. I put in drive and the solenoid is floppy...I can easily pull it and push the rod in the center of the solenoid.
You figure.... my car does not have any a/c.  I can't figure this one out.  Maybe its related to the transmission...some kind of switch or something.
abe

abe
1968 280SL Auto
Signal Red w Beige Int

[Roman Kishi]

There are two presser switched on the side of the transmission, both are connected to the CSS. Most likely one of them is not working properly, or the wires are loose. You can switch them around, and if your problem reverses ( CSS engage in drive but not in reverse) then "voila"

Roman
Northern Virginia
280 1969,Signal Red,Parchment Leather, Auto, A/C

[J. Huber]

Now Roman, that makes good sense! Sorry Abe, I was shooting for the obvious, sounds like it really is a headscratcher!

James
63 230SL

[abe280SL]

Roman you are my man....while I was gone I looked at all the electrical diagrams in my service manual.  I looks like one of the reverse light switch is somehow connected to the solenoid. The other connection is from the transmission oil pressure switch.  So I thought maybe the reverse light switch pathway is working properly but something wrong with the oil pressure switch. Then I saw your post....so maybe I am on the right path.  The only thing is that are you sure that reversing the pressure switches will do as you stated...or are they in series so that they both must work for forward to work.
I will try and see what happens and post in the next few days.
thank you
abe

abe
1968 280SL Auto
Signal Red w Beige Int

[graphic66]

The switches on the transmission switch to ground using pressure from the tranny. You can test them by putting the car in gear, while running and check at the switch to see if the wire is grounded. I jack the rear off the ground, apply the parking brake and crawl under with a long jumper wire from the pos. battery post and my test light to see if the switch is grounded. The two switches are located on the bottom left side of the transmission. Unhook the wires before checking to avoid a false ground through the solonoid. You can also just check continuity to ground, but going from the hot post on the battery is foolproof. My switch was bad this last Summer, lucky I have a parts tranny. I didn't try to fix the switch, it could have just been plugged with crud. Again, the car must be running and in gear to make this test. Just switching the wires will not affect the symptom if the switch is bad. You may want to just check quickly at the solonoid for ground while running in gear with your test light to the pos. side of the battery. My guess is you have a bad switch on the tranny, though. I don't know if you can buy a new one or not. If it is bad I would try cleaning the inlet real good and starting the car up with it unhooked in gear real quick to possibly blow some blockage out of the tranny line. You should get some fluid squirting out when you do this. the switches are easy to get in and out. You can also just switch the switches around to see if the problem changes from forward to reverse.

[abe280SL]

Graphic66, can I also connect the wire to that switch to ground and check to see if the solenoid works? I will be temporarily bypassing the pressure switch, but this will also tell me that the rest of the circuit/relays must be working properly.  I think if I do what you suggested and what I propose than I might be getting closer to an answere.  My fear is that if the switches are okay, and my ground  bypass does not work....then I am in big doodoo.
I will keep you posted and let you know what happens in the next few days.
thanks to all,
abe


abe
1968 280SL Auto
Signal Red w Beige Int

[graphic66]

Yes, just ground it out, at the tranny on both switches. This will check the wire from the switch to the solenoid. Your solenoid is working or it wouldn't work at all. I still think it is most likely the hydraulic switch on the tranny. Unless somebody unhooked the wire or broke the wire. This might help http://www.mercedesdismantlers.com/16BoltInstallationInstructions.html

[tuultyme]

My CSS was on all the time.  The wire first connected to the left oil pressure switch and than a wire ran over the transmission to the right oil pressure switch.  Somewhere over the transmission this wire was grounding itself.  I tried to pull out this wire it would not move so I just disconnected it and added a new wire.  Now it works correctly.

Bruce; 268Blaugrun(green) 1970 280SL; IL

[abe280SL]

Update....first thanks to ALL. I did the light test and both hydrolic switch turned on.  The right side (passenger) turns on when Drive, the left side(drivers) turns on in Reverse.  I guess the reason for two switches are that pressure builds up on one side vs the other side depending on D or R.

As mentioned above, the right side has a single wire the goes over the transmission and attaches to the left side where all the other transmission wires are at.  But I still had a problem...no solenoid activation on D only R.  Soooooo, as someone else suggested, I took out the pressure switches and reversed them.

Lord and behold....now I get solenoid activation on D but not R.  I suspect that even though the faulty pressure switch lights up..there must be poor contact inside and not enough grounding to activate the solenoid.

So the problem was a faulty pressure switch.  I will see if I can order one or mess around with it squirting WD40 and using an air gun to see if there is junk in there.

It took me 18 years to resolve this problem (well I ignored it)....this site was greatly helpful. Five years ago you were at the mercy of mechanics. Unfortunately, the good old ones
are dying out and fewer people understand these cars.  With this site....I FIXED IT!

One other thing, these old idle solenoid cost $400. Mine also had a difficult time activating when the pushrod was all the way in.  Sooo, I bought spring at the local warehouse and it keeps the rod slighty out, but not so much the it pushes the linkages.

Thanks again to all
Abe
1968 280SL Auto
Signal Red w Beige Int

[wwheeler]

One of my pressure switches is bad and needs replacing. When removing, should I expect a lot of transmission fluid to come out?

[Cees Klumper]

quote:Originally posted by wwheeler

One of my pressure switches is bad and needs replacing. When removing, should I expect a lot of transmission fluid to come out?

Just had this done, just a bit of fluid comes out, not much, and the whole procedure took less than 5 minutes on the lift.