Kickdown doesn't work, switch is new, what to check next?
 

'84 w123 300D turbo.

I'm finally taking over the blues mobile for some more DD duty. I'm wanting to solve the no trans kickdown problem. Sure I could search out the info but, for times sake, I'm throwing the question out again.

The trans shift fine. Up through the gears like it should, down through the gears like it should. Just when I want to hit the switch for high RPMs... Nothing.

I replaced the switch with a new one and that did nothing. I've been fiddling with the modulators and the cable to ge it shifting the way it is right now but still no vroom vroom.

Any ideas to what should be checked next will be appreciated.

P

Stumped??

What switch did you replace? If it is the electrical switch on top of the valve cover, I recall that is part of the EGR system. My 84 has a "Bowden" cable off the fuel linkage on top of the valve cover, which I understand is for the kickdown actuation. There is an adjustment on the cable. I haven't looked at what is at the tranny end, if that is where you replaced a switch. If so, I expect it would be internal to the tranny.

I swapped out the switch that is underneath the accelerator pedal. In my other BenZes when I hit the floor with the pedal it activates thus switch and makes the trans downshift (within the allowable RpM range). For example.. 3rd gear to second gear around 35 for all the acceleration it can possibly muster. Seems like it will make the trans hold gears for as long as Posible as well.

The shifting is mostly fine but this capability is lacking in the blues mobile.

It seems that these cars have that switch under the accelerator pedal as well as the cable on the throttle linkage. I wonder if there is an explanation somewhere of how this system works.

Maybe you need to adjust the cable on the valve cover. there is a plastic sleeve on the cable tucked into a nut that you can turn in or out depending on how you want the car to shift. I mess with mine once in a while. It is a white bolt looking thing on top of the valve cover attached to the throttle linkage stuff...it is NOT the part of the throttle linkage that activates the microswitch...as someone above has mentioned it's not, but rather further back towards the firewall. I usually stand on the passenger side of the car and view it from there. With our federal wagon it is very close to the back of the air cleaner housing. You will see the cable go down between the firewall and engine to the transmission.

Turn it one way for earlier shifts and turn it the other way for later shifts...(there is a link that is more specific as to which way to turn it for desired results)...sorry I can't remember. I have fiddled with it lots either way to get it dialed in to how I like the shifting. Maybe I should'nt do this? (can it harm the transmission?)

There must be some correlation bewtween the 2 sytems (the pedal switch and bowden cable)?,

or maybe that pedal switch just activates a solenoid to drop a gear when the pedal is depressed and thats it...(separate system entirely?)

If it is just wiring by itself and you have a new switch then maybe the wires themselves are shorted or unplugged at the transmission end. You could try to follow the wires. I think they go from the switch under the carpet through a gromett on the floor somewhere around the gas pedal to the transmission.

OR

Maybe they are part of the neutral safety switch wiring and someone has had to mess with it?

Does the car start in gear, or does it have to be in park to start it?


Someone that knows this system for sure might know, and will help out. I don't know for sure how it works...There could be some relays or some such thing up under the dash in the course of some of the wiring involved that is an intersecting point between the pedal switch and the transmission?

I am curious as well, to find out about this sytem.... On her 85 wagon it seems to work for the most part, but sometimes if I step on it at the wrong time it seems to drop all the way down to first...rev the **** out of it for a millisecond and then realize what it is doing, and shifts to the next gear.....sort of ....as if it IS working but just has a slight lag in reaction of the proper gear selection.

It would be nice to have the system working correctly since it does come in very handy for freeway merging and such...we need all the help we can get with the limited power.
I don't imagine that it is good for much of the components of the drive-train to be doing that kind of sudden shifting through three gears all at once either. I cringe when it happens and wait for the tranny to fall out....needless to say it has come down to avoiding stepping on the switch at the wrong time, which I have gotten used to doing, but sometimes forget if in a hurry and power is needed.

Tis a semi-automatic for you though? Do you just row the auto shifter through the gears then?...that seems to work for me sometimes...to avoid lugging the engine in the city.

722.3 Kick down
 

The foot switch is connected to a kick down solenoid that is attached to the rear of the transmission. My solenoid stuck in kick down mode and the tranny would not shift up. I got a used one from the junk yard.

Sorry I never did follow up on this thread. I fixed it.

Not sure the theory behind the solution but I tried something and it worked.

Pulled out one of those little vacuum orifices from the VCV circuit. A green one.

Solved the no lockdown problem right away.