Kickdown? - PeachParts Mercedes-Benz Forum

dkr · #1 09-24-2014, 02:24 AM

Well, after a hiatus from car work it looks like I'm getting back into it. This weekend I'm doing the oil filter housing gasket and the following weekend I'm planning to replace the o-rings on the turbo return line.

At present, I have noticed my '84 300D has not been downshifting at WOT. The transmission otherwise shifts very well up and down by itself. I normally notice it if I am on the freeway in 4th around 40mph and traffic clears up and I want to get up to 65-70mph. Instead of dropping into third, it just stays in 4th around 1700-2000rpm and slowly makes its way back to speed.

I have already lubricated the linkages as well as the accelerator pedal joint. My #14 fuse is in good shape and I tried swapping it with another white fuse for good measure.

I recently had my mechanic do the front seal on my transmission and mentioned the issue to him. He hooked a multimeter to the kickdown plug and mentioned it was getting good voltage.

I have tried manually pressing the kickdown switch and it is engaging (not stuck) both with my hand and when I press the accelerator all the way down.

Tomorrow, I'm planning to unplug the kickdown switch from the transmission and see if I experience any difference when I drive.

Is there anything else I can do to troubleshoot? It sounds like I may need a new kickdown solenoid if the switch is providing power to it although it would be nice to make a better diagnosis before just throwing new parts in...

Thanks,

Dkr.

rocky raccoon · #2 09-24-2014, 06:36 AM

An adjustment to the transmission kickdown cable may cure your problem.

Adjust using the white thumbscrew until there is just a little slack at closed throttle and try the kickdown. If not pleased at the result, adjust a little more in or out until it functions as you like. This is a non-critical adjustment.

Please come back to the forum with results as it adds to the data base.

Phillytwotank · #3 09-24-2014, 06:37 AM

Check your Bowden cable.

mach4 · #4 09-24-2014, 11:11 AM

I'd crawl under the car so you can see and feel the kickdown and have someone press the switch in the car. You might want to double check the voltage just to be sure.

I believe that you can check the operation of the kickdown solenoid by removing it and activating the switch (make sure it's grounded)

If the solenoid activates and the plunger moves, it's something internal to the trans, otherwise a new solenoid is probably the solution.

cooljjay · #5 09-25-2014, 01:52 AM

Best way to test the kick down switch, if you don't want to remove it and test it at the battery is to crawl under the car and have someone actvate it with the peddle as was said, you will hear the valve click. If you don't have anyone to press the peddle, crawl under the car, undo the screw/wire, unplug the switch jump the pins, crawl back under and touch the wire to where it was connected and listed for the kick.

If you have the bowden cable, that may well be it. I would also check the gear shifter bushings, 4 total and I would also make sure all your linkages are adjusted to the manual.

cfh · #6 09-25-2014, 08:19 AM

Could someone explain how the bowden cable affects the kickdown operation, vs. the kickdown switch / solenoid? In my thinking, the kickdown solenoid would be doing all the work here. How would the bowden cable help make the downshift happen?

cooljjay · #7 09-26-2014, 11:12 PM

On the transmissions that have a bowden cable, vacuum and a kick down. The cable tells when the transmission when to shift, the vacuum controls shifting and the kick down allows you to kick the transmission down a gear.