Hi all, in the middle of a long road trip the tranny stopped downshiffting by use of the kickdown switch... dont know alot about it but here is what I ve checked so far.. I pulled the switch and it does function . ran a volt meter accross the two wires attached to the terminal with igntitiion on.. NOTHING.. there is 12 vdc accross one with the other to ground.. what else could it be... any info will be greatly appreciated thanks Joe

I adjusted the slack out of the bowden cable (coming up from the tranny to the top of the valve cover back towards the firewall) and that helped w/ kickdowns (you know - when you floor it!) for passing.

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Can anyone verify that one wire on the kickdown switch is ground?????? and the other is 12vdc.... if one side is ground then thats my problem I would think. since I dont get 12 vdc accross the 2.... only when I ground one to the frame... thanks all

disreguard the last... it couild not be ground... that would short out everything.. guess im getting ahead of myself... but what would the other wire go to?

aa

All the switch does is to pass power to the kickdown solenoid. Turn the ignition on and press the switch, you should hear the soldnoid click.

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thanks. that makes sense.... I checked and there is 12 vdc going to the solenoid.. I dont here a click.. assume the solenoid is bad...are they pretty easy to fix cant find a thread on r/r the solenoid... before I do that is there anything else that can be done.. again there is 12vdc at the tranny solenoid when the switch is activated.. thanks so much


Joe

JoePilot,

I was recently troubleshooting the kickdown system on my 80 300D non-turbo and found the electric kick downswitch under the accelerator works the same as you have already discovered yours does.

And then I verified the solenoid on the tranny was properly receiving the +12V the kickdown switch was send it.

THEN I removed the solenoid [ collecting the ~2 qts of red Dexron III fluid that drained out ]. I found that I could bench est the solenoid by connecting it directly to the battery and blowing air [ or vacuum ] through the small “snout” that is one of the opening of this simple electrically hydraulic “on/off ” valve.

CAUTION… do not leave the solenoid electrically powered for too long a time for like an irrigation control the cooling of the heat generated in the solenoid might depend upon it being fully installed ! I have see these small solenoids swell up and ooze “goo” if left powered off of the valve plunger that it is designed to move !

Yes, this procedure is little work but worth it to me… for I have NOT even been able to find such solenoid valves listed on any of the parts WebSites I tried !

Hope this helps,
Sam // Novato, CA

thanks Sam, I will be doing just what you suggested. how does the solenoid valve come out??? is it self explanatory... thanks Joe

Joe,
Your are correct, removal is a no brainer... just remember to be ready with a pan big enough to catch the ~2 Quarts of tranmission fluid. If you have not serviced the tranny for some time, it would be a good time to drain it and the torq converter [ ~7 qts/ltrs of Dexron III ] AND put in a filter kit which will have the pan gasket and sealing rings/washers for dip stick tube and plug on torq converter. This would also let you blow back through the hole where you remove the kickdown solenoid. While you have the solenoid out, take it down to a local well equipped parts store and see if you can replace the two O-rings on the solenoid... that is if it bench tests OK. If it is bad, good luck on finding one... and if you do end up going this route, let us know here on this thread.
Sam

I've had the solenoid problem and the dealer had them in stock.

Jim W.

You have correctly identified the problem; the black wire which feeds the kick down solenoid is also the ground for that system
The solenoid body is an electromechanical relay, in contact with the solenoid valve, grounded thru the transmission case

On a functional system the voltmeter should read source voltage when concected to the KD switch wires.. There is a break in the wire or the solenoid body is defective.
You can check for resistance with the solenoid wire connected, you should have 14 to 15 ohms, or jump the KD switch wires
and measure for source voltage at the solenoid wire, no voltage broken wire, voltage defective KD solenoid.

C32AMG & Joe,
I know that Joe's is an 80' 300SD and what I am dealing with is a 300D but I find it hard to believe that the tranny's kickdown solenoid design would be reverse of one another. My solenoid is definitely supplied + voltage over the single wire coming from the kickdown switch under the accellerator.

Just think about it, I have removed my solenoit and it only has a single conductor... and it bench tested just fine when +12 was applied to the wire and the solenoid's body was connected to negative. It is my belief that any electrical component with a single wire should receive +12 over that wire... unless the component is somehow isolated from the car's chassis!
Sam

[IMG]http://www.mastertechtrans.com/post/kd2.jpg


You have correctly identified the problem; the black wire which feeds the kick down solenoid is also the ground for that system, the solenoid body is an electromechanical relay, in contact with the solenoid valve, grounded thru the transmission case.

Sam,
Here is what I mean by the above statement.

Yes you are right; the single wire going to the KD solenoid, supplies the necessary operating voltage, once that VOLTAGE is consumed by the load place on it, the solenoid coil in the body moving the solenoid valve piddle, Electromechanical Relay, it continues to flow thru that circuit, becoming the circuit ground side, transmission case back to the battery completing the closed loop. As Illustrated below.

Picture #1 is a voltage reading In a car, using the KD switch power supply wire, and feed wire which goes too the KD solenoid on the transmission as the ground source.




Picture 2, channel 2 is the voltage into the KD solenoid, 13.86 volts is power flow to the solenoid

Channel 1 is the KD solenoid ground side. 0.12v is the voltage dropped by the load, ground side.

I hope this helps.

but I guess your use of the special diagnostic "Snap-On" tester has us speaking different electrical languages.

I tend to be very basic... using an old fashioned multimeter mostly [ however I have been know to use a modern digital meter too... but they often don't let me zero out on continuity checks].
Heck, I'm even partial to separate stand alone ampmeters!

Seriously, I honestly could NOT follow your explanation... but the main thing is that we are in agreement even if we are seemingly speaking a different language!
Thanks for your input.
Sam // Novato, CA