Author Topic: Maybe a solenoid? (Read 4172 times)

Tom in seattle · « **on:** June 11, 2019, 17:28:53 »

I have been reading, researching, the cause of a solid “clunk” as my auto trans comes to a stop. I’m pretty sure my linkage and, ignition advance and air fuel mix are good. But there is a mention of a solenoid on the intake plenum. I’m enclosing a photo of a possible miscreant as it has two wire connections on it but no wires attached. Is this a source or contribution to my problem?

Benz Dr. · « **Reply #1 on:** June 11, 2019, 17:48:35 »

No wires going to a switch that should be hooked up is your problem. That throttle position switch controls the solenoid that changes modulator pressure.

Pawel66 · « **Reply #2 on:** June 11, 2019, 19:18:59 »

Tom, no picture was attached to your note.
Benz Dr. is referring to the throttle switch. This switch affects the gear box modulator pressure.

I think you might be referring to Constant Speed Solenoid. I marked two possible positions (red line shows where you could have it). If you refer to this solenoid, it may or may not be meant for working with your gear box. Sometimes it was installed without being connected on the US cars. it is to increase idle speed when the gear is engaged or when the AC is turned on. But in your car it may not perform any function other than you can sell it for nice money and raise funds for something else.

But seriously - you would have to find out if you need it or not. If you engage gear and the engine keeps constant idle - you probably do not need it for this. If you have no AC - you do not need it for AC.

I do not hink it is responsible for clunk (but maybe someone will correct me). The responsibility for clunk may lay with solenoid on the gear box, throttle switch that steers it and modulator pressure, I think, if the other items you mentioned are ok.

ja17 · « **Reply #3 on:** June 12, 2019, 02:06:53 »

The transmission modulator pressure must be lowered by the three position solenoid and its linkage as the car prepares to stop or a hard shift (clunk) will occur. If you remove the interior access cover on the tunnel (right side), you can observe it's movements. Make sure it moves to the rearmost position when the accelerator pedal is fully released.

Tom in seattle · « **Reply #4 on:** June 13, 2019, 08:07:31 »

Pawell: thank you, it is the throttle position switch (white directive) located front right of the other red notation. I have no A/C. However the car is a Euro car originally a 4 speed, now with auto trans. As directed by Joe, I have had the tunnel cover off and removed the inspection plate on the right side and apparently was looking in the wrong place, saw nothing. I will try again. I thought I should only see the 3.position solenoid with the trans out of the car. Unfortunately the photo is not on the device I am using today. I will try later in the week another photo.

mbzse · « **Reply #5 on:** June 13, 2019, 08:18:23 »

Quote from: Tom in seattle

.../... had the tunnel cover off and removed the inspection plate on the right side and apparently was looking in the wrong place, saw nothing.../...

Tom, this is what you are presented with when you have removed the cover plate. The three-way solenoid is what the lever arm is attached to

ja17 · « **Reply #6 on:** June 13, 2019, 14:53:44 »

Nice picture, thanks Hans. Tom the solenoid linkage should move to the rear-most position when the accelerator pedal is released (ignition on). With the ignition off, the linkage rod moves one position forward (middle position). Center position also happens with the ignition on and the accelerator pressed above idle. Center position is normal rest when the ignition is off. So if your inputs to the solenoid are not happening, your transmission may be staying in center position all the time. Front-most position may only happen when the ignition is on and the "kick-down" button is depressed (under accelerator pedal). Rust and corrosion of the trans linkages and sockets may prevent movement also.

Benz Dr. · « **Reply #7 on:** June 13, 2019, 15:12:52 »

I've seen where the small arm coming out of the solenoid will seize up. This is a fairly common problem and it can usually be fixed by removing the solenoid and then taking the end cap off. The arm hinges on a small brass bushing and this is where you will find the problem.

Easiest way to test if all is working is to turn on your ignition and then reach under your gas pedal to push the kick down switch. You should hear a fairly loud click when you do that and if you hear nothing then something isn't working. Check to make sure you have power going to the kick down switch before moving on to other possibilities.

cfm65@me.com · « **Reply #8 on:** June 17, 2019, 14:17:21 »

Hi Gents,
May I please pop in here and ask a relevant question to Dan and Joe?
Turning ign on, the rod move to the aft position and should move to the mid position when R or D is selected, etc
My 250SL auto does not move to the mid position on selecting R, however all other selections including the kick down seems to operate correctly.
Could it be the Reverse oil press switch and which one is it, the Left or Right switch?
Regards
Chris

Tom in seattle · « **Reply #9 on:** June 26, 2019, 23:32:01 »

With both inspection plates removed and after a liberal dose of engine cleaner and water I went for a ride, flashlight in hand. The long arm from the solenoid did not move at all. I tried to get the socket off the ball at the solenoid but quit when I thought I may deform something. Accordingly I can’t say if the rod could be moved independently of the solenoid. I popped the water tight grommet off the solenoid thinking I may see loose wire connections but see it is a wired at factory loom. On suggestion from Benz Dr I turned the key on and depressed the kick down switch and DID hear click which I confirmed was the solenoid by feeling a movement on the solenoid body. I think I have traced the solenoid wire loom to three independent wire connections on the lower left side of the transmission. So maybe my next step should be to see if I can remove the solenoid to see if the movement is restricted at the connection site as suggested by Benz Dr. I’m not sure if this matters, but the trans goes through all the gears, kicks down etc but just makes the Klunk I’m trying to sort out.

Tom in seattle · « **Reply #10 on:** June 26, 2019, 23:52:16 »

I am posting photos of what may be a throttle position sensor. There are no wires attached or nearby. I do not have A/C and the car idles well at rest and in gear so no rev increase needed. But if this has something to do with why the 3 position solenoid is not operating, then I need to understand more. And I’m grateful for your assistance.

Tom in seattle · « **Reply #11 on:** June 27, 2019, 06:06:33 »

As I’ve described to Joe, I depress the kick down switch ( with key on) and there is a click, but not loud. It does not result in the solenoid moving the long shaft to the trans. I’m just guessing that the solenoid is trying to move the shaft but what I am hearing is a small amount of free play somewhere, probably just within the solenoid. I think I see that the solenoid has a bolt on the left and right side, just 2. Should I be able to remove the 2 bolts and disconnect the ball and socket coupling to work with it? Am I correct to assume I could disconnect the wire loom from the 3 connectors by the lower left front of the trans?

I note that the wiring contains 3 wires. Probably a ground and one wire pushes the solenoid out and the other pulls it in? Does this explain the 3 positions of travel for the long rod going back down the inspection plate on the right side of the trans tunnel?

ja17 · « **Reply #12 on:** June 27, 2019, 06:49:39 »

The transmission linkage ball ends, use a special "wire lock clip" to keep them from accidentally coming apart. They will not separate with the clip in place. I have seen some standard transmission pagodas which use the microswitch on the firewall linkage to operate the transmission three position solenoid on the transmission instead of the venturi switch. Is this your situation?

Tom in seattle · « **Reply #13 on:** July 19, 2019, 19:58:41 »

JA and Benz Dr and others: I'm still working this problem. I have removed the 3 position solenoid, removed the lever cap and inspected and greased it. I believe it works freely and is not defective . There are 4 wires coming from the solenoid (2 brown ground) and a black and a white wire. Energizing the black and white wires causes the solenoid to push or pull from the center position. I previously posted a photo of the switch that is connected to the throttle plate arm. It is not connected to anything but I did test it and the switch is closed when the throttle plate is closed (energy passes through) and open when the throttle plate is open. Am I correct in guessing, As Benz Dr advises, that this switch should be wired to the solenoid to cause it to move to forward or rearward position? If I were to do this, the solenoid would be energized whenever the engine is at idle and irrespective of the position of the transmission shift selector (park, neutral, reverse or forward). Would this be correct or would the energy be somehow selectable only from a particular forward or reverse gear?I not that I have found pretty good wiring information in the technical manual. It appears that running a wire from #3 fuse to the throttle position switch and then back to the (push back) wire from the solenoid would cause the solenoid to engage any time the throttle is depresses. Should I do it this way? As I have said earlier there is no wiring to the throttle switch now.

My next question is with regard to the long shaft that is normally connected to the solenoid and runs back to the transmission as observed from the inspection plate on the right side of the tunnel. If I grasp the shaft I can move it a little forward it seems "free" with little resistance. If I move it to the rear a little it feels like there is a spring load which can be moved with some pressure, more than the amount of pressure deliverable by the solenoid. Does this seem correct to you? There is discussion in the tech manual about a spring loading but otherwise the shaft can be easily moved forward and back but light finger pressure.. I believe that the action of this rod may have been obstructed by rust at its upper connection which I have now freed up.

Thanks for sticking with me.

Pawel66 · « **Reply #14 on:** July 20, 2019, 10:39:11 »

Tom, just in the interest of time of the more experienced Members who can then focus on helping you with your particular issue, let me try to describe how the simple Euro (no emissions control) arrangement works - it helps understand what drives what. This is not to offend anybody, just maybe to sort things.

The position of the three way solenoid determines the position of pressure modulator and is setting the pressure in gear box for downshifting in particular moments or upshifting in particualr moments.

This position of the three-way solenoid is governed by throttle switch and kick-down switch. (Joe asked you if you perhaps have another arrangement - firewall switch that replaces throttle switch on some cars. Note: the presence of throttle switch does not mean it is used by car - factory were sometimes fitting it regardless if it was needed or not, same with CSS).

The "zero" position: ignition off. The three-way solenoid is in the middle position (spring is there). Throttle switch is closed.
1. Ignition on: throttle switch closed, so the three-way solenoid gets power through it, the rod moves backward.
2. Gear selected: nothing happens to three-position solenoid. CSS pushes the linkage a bit so that the engine does not stall under load. Throttle switch still closed.
3. You press the gas pedal as you want to drive. Throttle switch opens, three position solenoid goes to middle position to change the pressure. Transmission is ready to shift up.
4. You accelerate, transmission is shifting up. Throttle switch open all the time.
5. You want to really speed up and floor it - the kick-down switch gives power to the three-way solenoid, it moves forward and enables downshift. Throttle switch open all the time.
6. You want to slow down - you let your foot off the gas pedal. Throttle switch closes. Three way solenoid moves aft where it causes the pressure to allow downshift as you slow down.

Here, if you have the throttle switch misadjusted and it will still be open, tranny thinks the car is doing something different than it is doing. Tranny is set to upshift, car is slowing down and has to downshift - you get rough downshift and clunks.

7. You stop and select P - throttle switch closed (as you let your foot off the gas pedal earlier), CSS disengages, linkage goes back to idle. Three way solenoid is aft as before, no change.

Selecting gear is not affecting directly the three-way solenoid position - only if it causes throttle switch open or close through the linkage movement caused by CSS - but throttle switch should be adjusted so that it does not happen. Throttle switch should open right when you move gas pedal from the "CSS extended" position and after slack.

The three wires coming to the three-way solenoid are: +from throttle switch, + from kick-down switch and ground. The other green/red wires are from pressure switches (left and right) that meet on the contact plate with a wire that goes to CSS and provides the ground to CSS.

Throttle switch and kick-down switch get power from fuse 3. CSS gets power from fuse 5.

Throttle switch is adjustable, so is the kick down switch, so is the CSS.

Certainly the upshifting or downshifting of the tranny while driving depends, as tranny is steered by vacuum, also on things like: load (driving up the hill, down the hill, etc.), driving style (e.g. faster or moderate acceleration) and probably many other factors, of which car being in tune to deliver good vacuum is probably the most critical.

I hope I did not mess anything - if so, please correct me.

If emissions installation is there - it looks probably different in terms what steers what, principles remain the same, I think.

Shvegel · « **Reply #15 on:** July 20, 2019, 11:27:36 »

Tom,
Sorry for chiming in so late but I think the crux of the problem lies very early in your thread when you said your car was formerly a manual transmission car that was converted to automatic. I am wondering if and of the circuitry for the 3 position solenoid was added at all? This is a very simple circuit that supplies power to the solenoid from fuse 3. Power is supplied to the three position solenoid from the throttle position switch and the kickdown switch (which should be screwed into the floor under the accelerator pedal accessible from under the car).

Think of the wiring in you solenoid as a "Y". Ground is supplied up the trunk of the Y and depending on which branch you power it energizes the solenoid in one direction or the other. The brown wires are the trunk and should have a large ring terminal on them? There is a good ground behind the engine on the driver's side. There is a large cable bolted to a bare spot on the chassis that runs to the bell housing of the transmission. Connect your ground there.

The White wire should have a medium sized ring terminal on it and be connected to one terminal of the throttle position switch (you posted the picture of it) with the other terminal of the switch going to fuse 3.

The black wire should have a small ring terminal and should be connected to one terminal of the kickdown switch(If it is there?) with the other terminal of the kickdown switch connected to fuse 3.

If every thing is connected correctly with the key on and engine off the solenoid arm should be in the rearmost position. When you start to apply throttle it should move forward one position and when you push the pedal to the floor it should move forward one more notch.

A word of caution regarding the throttle position switch. It is fragile and VERY expensive ($900) When connecting wires etc make sure the ring terminals are the proper size and don't get crazy tightening the screws. If for some reason the rod doesn't move rearward when you lift off the gas that switch might just be dirty. It can be disassembled and cleaned if need be.

Tom in seattle · « **Reply #16 on:** July 22, 2019, 01:31:25 »

Shvegal and Pawell: thank you for your lucid responses. Yes, my car started life as a manual trans and converted to automatic, probably in Amsterdam. It does have the throttle switch but it was not wired in. I've tested it though and it appears functional. My 3 position solenoid was rusted into an unmovable position. I removed it, cleaned and tested it and it now works. So I'm ready to wire in the throttle switch and put everything back together. Based on my reading of the tech manual, my car exhibits the flaws that are described as the result of a non-operational solenoid. In the case of the kick down switch, the car did kick down, but the shaft to the rear of the trans did not move because the snap pivot was rusted but with engine not running I could hear a click in the solenoid. After cleaning, the solenoid seems OK.

I was concerned that having the solenoid operating whenever the throttle switch was closed (engine idling etc) that the solenoid might over heat. But I guess the MB folks have taken that into consideration and I should just wire it in as key on operational.

Thanks for your help.

Pawel66 · « **Reply #17 on:** July 22, 2019, 04:37:31 »

The concern expressed by experienced Members was rather about the contacts in the throttle switch that need to cope with high amperage every time you press the gas pedal - quite often if you think about it.

As this switch is a rare and expensive part, a simple relay solution can be easily applied.

Tom in seattle · « **Reply #18 on:** August 19, 2019, 21:54:03 »

Shvegel and others: yes, your understanding is correct. The modulation solenoid was never hooked up. My car does have a throttle position switch and also a kickdown switch. The car did kick down but the modulation solenoid was rusted in position and neither wired or capable of moving.
I have drawn a wire diagram which I believe displays the needed wiring. But I still have a question. The wiring block on the side of the transmission has one larger screw in the center and one smaller screw to the rear and these are for the solenoid wires. There is a screw forward of the center . This screw has been broken off and I will try to drill and attempt to extract it. Do you think this screw was intended to accept the power wire from fuse 3 and wires going to the throttle switch and kickdown switch? At first I considered it as possibly a ground terminal but since the modulation solenoid is grounded to the transmission it would seem redundant there beca ground at the terminal block and its shielding walls explain better that it be used as a 12 volt connection point.

My expectation is that the wiring block is just that and is not connected to wiring within the transmission, just to the throttle position solenoid. Am I thinking about this properly?

Please critique me.

Benz Dr. · « **Reply #19 on:** August 20, 2019, 02:37:07 »

If I remember correctly, that block has three different sized screws in it so that you can't get the wires mixed up so easily. Large at the front going to smaller at the back. Not sure if this is any help or not but thought you might like to know.

Pawel66 · « **Reply #20 on:** August 20, 2019, 09:45:49 »

Small screw - positive from kick-down switch (kick down switch is powered from fuse 5)
Medium screw - positive from throttle switch (throttle switch is powered from fuse 3)
Large screw - ground

Pressure switches for CSS - wire from right above transmission to left then to CSS, providing ground (either D or Reverse). CSS has power from fuse 5.

No, no connections underneath the terminal block to transmission. The only connections on the terminal block are harness from the car and a short "tail" from three position solenoid - eyelets from both meet on the screws on the terminal. Eyelets sizes correspond to screw sizes.

There is a cover that is attached to the terminal block - sometimes missing. I bough it in MB a couple of years ago.

Tom in seattle · « **Reply #21 on:** September 17, 2019, 03:14:55 »

I wish to report back: together we have made notable progress. I now have a operational modulation solenoid which moves the slide bar on the transmission forward and back. My original grievance was that the down shift was clunking. There is a notable improvement which seems to be getting better with some driving. If I quickly de accelerate it will still clunk a bit but usually is much better and with normal de acceleration usually not.

I am noting that maybe a trans pressure adjustment is warranted. Mine will up shift at a bit over 3000 rpm from 2 to 3 and as high as 3500 from 3 to 4. That seems a bit high and my heart symbiosis would appreciate a lower shift points. Down shifts from 4 to 3 are aggressive but I rarely use it. I'm just not used to a car which runs on the freeway at 3500 to generate 60 mph.

Are my expectations wrong?

News:

Author Topic: Maybe a solenoid? (Read 4172 times)