Kick Down Switch going wild

[Artkez]

Hi - Just a quick question  - I've noticed this issue ever since i have had the car,  280 sl Automatic 1969

If i accidently hit and engage the kick down switch, it works and drops the gear studently  and aggressively ,  the car does down shift to the lower gear but the problem is that the transmission goes wild and remains in the lower gear and is VERY Rough and seems to be locked in a lower gear and shifts at the wrong spots.
 It is not Drivable,

i have to pull over  stop the car and turn off the engine  wait  a minute then restart the car and all is normal. Once i do this  all is well again and the shifting is very smooth

Something seems to reset while i turn off the car .  Does the Solenoid reset   Does the switch stay in the engaged ON position ?? 
I am tempted to disengage the kick down switch , seems like you would rarely use it, because it seems very aggressive  and jolting result during the down shift

Truly appreciate your help and thoughts

Arthur

[ctaylor738]

It could be that the switch is sticking, or the three-position solenoid is sticking, or the linkage isn't moving freely, or the kickdown pressure needs adjustment.

You can get the same effect as a kickdown by moving the shifter to "3."

Cheers,

CT

[Artkez]

Thanks Chuck, 

I appreciate your recommendations.  The fact that  if i turn off the engine  and restart it seems to me to be a reset type of effect. 

Do you think the pressure  for  the kick down switch is altered after turning  off the engine ??

Does the Solenoid get reset buy turning off the engine ? 

Seems that the switch is not sticking since it immediately goes back to normal after turning off the engine

Is there an easy way to turn off the kick down switch ??

Thanks   Arthur

[BobH]

Hello, you can simply unplug the kickdown switch, you'll find the plug low down in the engine bay, the other side of the bulkhead to the actual switch

However, as Chuck says, if you ever manually shift down, perhaps to overtake, or climb a hill, you may experience the same symptoms, so probably best to address the main cause. Have a look at "Rough Shifting" on here:

https://www.sl113.org/wiki/Automatic/Start

[Artkez]

Bob and Chuck

Thanks for all the inrfo and the link to the discussion a bit over my head but great tips

I will try to disconnect the kick down switch, but  i am not certain that i was hitting the switch , since i looked at it  today on the carpet and it seemed that i really have to depress the accelerator  to a very large extend to hit the switch.

Can the transmission down shift when it senses  that i am trying to accelerate  without hitting the kick down shift ??
Is there any mechanism in our transmission that will downshift  as the accelerator pedal is depressed quicky and deeply  as in trying to pass another vehicle  and all the while the kickdown switch is unplugged  ?

Thanks

Arthur

[Cees Klumper]

Yes the trans can shift down without engaging the kickdown switch, based on the combination of speed and load on the engine. It's based on several factors. Best to diagnose and correct methodically, refer to the technical manual write ups on the transmission controls and systems, things like the 3-position switch, solenoids, off-idle switch, modulator pressure, engine vacuum.

[Artkez]

CEES
Thank you so much for your reply and comments I will test drive this morning and keep you posted I'm hoping it's going to be better with the kickdown switch disengaged thanks Arthur

[Artkez]

Hello all  and thanks for your interest,

I did my test drive today.  the engine was replaced  with a 1979 280 se sedan engine, the car runs very nice and it has a lot more power than before and no noise       see Steve's (my son and co owner of the car )  posting last week  regarding the engine swap        https://www.sl113.org/forums/index.php?topic=38260.0

i carefully remove the 2 prong connector to the kick down switch, thus this switch is no longer operable and will not effect the transmission.  Thanks for the description of the location , it was very easy.

I drove the care and the shifting was very smooth and easy and peppy .  if  i accelerate from a stop and try to race someone on on the road  all is fine , it shifts  with no problem . 

The problem occurs when i am going 30 miles per hour and i push the accelerator pedal and try to pass some  in front of me.  The transmission down shifts and the RPM goes up  to about 3,800 and the car beautifully accelerates and i am successful in passing the car in front of me.

 Problem is  that the transmission is  still in the "DOWN SHIFT MODE"  ITS ALL SCREWED UP !!!  you come to a stop and it acts crazy, does not shift still 3,000 rpm  with very Heavy thumping sounds   the car is not drive able  it appears as if someone has thrown  a wrench inside the transmission

To cure the Problem if you turn OFF and ON the ignition  of the car then miraculously  all gets better the transmission is like new again and shifts nicely , quietly at perfect speeds.

The transmission appears to downshift correctly based on the accelerator being suddenly depressed but it does not RESET back to normal until i am able to Turn On / off the care then it appears to reset back to perfect normal condition.

How does this happen

This transmission has been rebuilt about  7 years ago with very little mileage place on the car.

Is there an electrical module that may be broken that does not allow the to reset   I think you mentioned a solenoid that could cause this problem???  Also  the transmission is my original one from the  69 SL and this problem we noticed as well while driving the SL 6 months ago. 

I would love to try some adjustments and module replacements  by a mechanic  before  we remove it and send it off to a transmission shop.

 My mechanic really did not know that turning the car ON and Off would reset this issue and did not know  what could  this problem of the transmission not resetting after a "Kick Down Action".

It seems that there is something electrical or pressure  being sent to transmission and it is not able to stop sending this message until all electrical is off ?

We truly appreciate your help and  would love to know if this problem is a common one with our transmissions

Thanks   Arthur and Steve

[Pawel66]

Have you studied Technical Manual about how to adjust the transmission as per the link provided?

I think all is there, starting with making sure the three way solenoid works properly, pressure adjustments and throttle switch adjustment.

I am not a mechanic, but I was able to do all this just following the steps from the Manual.

Important point is that your engine has to be in tune 100% and brake booster has to be good 100% as the gearbox is controlled by vacuum as well as by electric means.

[BobH]

....To cure the Problem if you turn OFF and ON the ignition  of the car then miraculously  all gets better the transmission is like new again and shifts nicely , quietly at perfect speeds.

The transmission appears to downshift correctly based on the accelerator being suddenly depressed but it does not RESET back to normal until i am able to Turn On / off the care then it appears to reset back to perfect normal condition.

How does this happen

It seems that there is something electrical or pressure  being sent to transmission and it is not able to stop sending this message until all electrical is off ?

Hello, once the engine is switched off, all electrical connections to the solenoid and other equipment is removed, the pressure goes back to zero, hence everything resets until the sequence starts again.  The experience sounds quite startling, but hopefully if everything is correctly adjusted it will perform as designed without any major work involved

[Cees Klumper]

Arthur and Steve, there's likely not too much wrong with the transmission. But, as several have noted, there is a lot of information in the technical manual that explains how everything works, should be adjusted etc and there are no easy shortcuts - generally, unless you are very lucky and the first thing you check happens to be the cause. We can't really help you much further, without being with you and going through all the various components and checks. If you bring the car to a mechanic, unless they happen to be experts on this era Mercedes, they are going to have to go through all the same steps (and unless they have access to this forum, or an equivalent good source of information), could take longer to find the issue than you can yourself. So best is to read up on how it all works in the technical manual, print out what you need, and 'have at it' step by step. 95% chance you will identify and be able to fix the issue yourselves.

[Artkez]

Cees, Bob and Pawel.

Thanks so much for the  feedback and recommendations,  i will print out the manual and see if my mechanic  or his transmission guy is comfortable in adjusting it and following the steps

Is this the  link ?

"""""Have a look at "Rough Shifting" on here:

https://www.sl113.org/wiki/Automatic/Start[/""""


Thanks   Arthur

[Pawel66]

Yes, it is, you just have subsections there. I would focus on:

1. Throttle Switch adjustment. it is not well described there, so here is the better link, please study this: https://www.sl113.org/forums/index.php?topic=26120.msg188454#msg188454
2. Overall operation/position of the three-way solenoid (Installation and Adjustment Instructions)
3. Modulator pressures. Since I came across some mistakes there, I am attaching pressures required. The mechanic will need a banjo bolt connection to check modulator pressure. I am also attaching a link o thread, where in the picture in Reply no.1 you will see where on transmission you have the port to connect pressure gauge (picture is upside down). https://www.sl113.org/forums/index.php?topic=29573.msg213949#msg213949

I hope if you go through 1 and 2, perhaps you will not need to go to point 3.

I am not a mechanic (disclaimer!), but from your description, if I were you, I would start from throttle switch adjustment - when you remove foot from gas pedal, it is the throttle switch that is responsible for bringing transmission to downshift mode on deceleration.

The condition for all this is to have a good vacuum. Good vacuum at idle and when brake booster is activated. Vacuum operates this gearbox. To have a good vacuum at idle, you have to have tuned engine with properly adjusted idle - maybe followo the Linkage Tour first if you are not sure.

[Artkez]

Pawel

Thanks so much for all the detail explanation and documentation,  I will read as much as i can and hope to find a mechanic that i can communicate this knowledge.  i guess to start slow and methodical as you point out.
Also the mechanic that did my recent engine swap from  280se   70 sedan to my 69  280sl  is from Poland  -  very nice guy
 Next trip to California  both of you should meet

Thanks   Arthur

[Pawel66]

Hope he does a good job!

Again, I am not a mechanic, I can help get to sources, but others here can provide a professional advise.

If it comes to pressure adjustment (I hope it will not), remember to disconnect vacuum, probably it is easiest done at the intake manifold.

[Artkez]

Pawel

Tank you will keep you posted

Arthur

[Pawel66]

If your guy needs a chat in Polish on this, let me know.

[Artkez]

Pawel,  that will be great and fun in Polish

Arthur

[Artkez]

Cees and Pawel,

Quick question -   I know that both of you mentioned that if you disconnect the kick down switch the transmission  is still able to downshift when it is necessary .

 Can you explain to me how this  mechanism occurs  i assume  you start with the accelerator pedal, you punch it , press it abruptly and with deeper than normal pressure and penetration , the car downshift  to 3rd gear from 4th gear and the RPMs increase and you are able to quickly increase your speed and efficiently  pass the car ahead of you.

Can you explain to me exactly what  happens and what type of electrical message is send to the transmission or what type electrical components are used to make this event happen ??

Seems impressive that a 1965 - 69 transmission can make this happen

Thanks for your knowledge and insights

Arthur

[georgem]

Hi Artkez
No electronic wizardry - -all old school vacuum and pressure pipes to the gearbox as far as I know.

[Cees Klumper]

As georgem says it, my understanding is it is based on engine vacuum combined with load on the engine. When I installed my rebuilt engine, the transmission shifted differently, I assume due to the difference in vacuum produced. I think all the information is in the technical manual, as for what to check, how things are supposed to function, it's just a matter of digging in and following all the information provided, or getting a professional mechanic to do all that for you.
As for the downshifting without a kickdown, just compare it to what happens when you slow down and the transmission is in fourth. Depending on what speed you slow down to, the transmission will downshift to a lower gear without you depressing the kickdown switch (obviously) or even applying a certain amount of throttle. It just downshifts to where you need it to 'automatically', to be able to re-accelerate. If you come to a complete stop, it 'knows' it should go to second gear (assuming the whole system is not completely out of adjustment or broken). That's probably happening with your car at the moment, so that's why I speculated there's probably not that much wrong, just one or more of the many components that is/are misadjusted, not connected properly, stuck etc etc

[Artkez]

Thanks all  for input, i probably drop it off next weeks and see if he can make a few adjustments.

Cees - actually i have learned how to drive the car  and do not aggressively or abruptly press the accelerator pedal and its a real pleasure to drive .  No downshifting occurs and the transmission does not "freeze up" 

It has great power  I can go from 0 mph to 60 mph with great power and great shifting, so the upshifting works well, it the downshifting (similar to abruptly depressing the accelerator  passing a car at 50mph) does not work and causes the transmission to lock up or act crazy  . 

Good new is i know how to reset it,   I just turn off the engine and restart it and all is back to normal and transmission works great after the reset.

I'll have it checked out next week and keep you guys posted


thanks so much    Arthur