Bypassing Downshift Switch - PeachParts Mercedes-Benz Forum

stingc · #1 10-30-2004, 02:50 AM

I have an 86 300E, and the downshift switch recently started to stick. Fixing that wasn't a problem, but I found that I really liked driving the car with the switch stuck down. So I'm wondering whether it would be ok to wire in a switch to make the car think I'm flooring it when I'm not. Since it is only designed to be activated at WOT, I'm worried that it might change the timing or AF ratio enough to eventually damage the engine at part throttle (it feels like it affects more than just gear selection).

C32AMG · #2 10-31-2004, 09:42 AM

Installing a parallel bypass switch in the kick down circuit will enhance the performance of your car. The transmission will shift later at medium and full throttle and the down shifts will happen sooner, depending on throttle opening. The best performance benefit in some models cars would be commanding a 1st gear start in the transmission. You will consume more gas with that added power.

BENZ TEK · #3 11-14-2004, 04:12 PM

Watch yourself when bypassing the kickdown swith. The transmission will never shift to 4th when you're on the highway. You are almost guaranteed to burn it up. Most of the mercedes rebuilders of tranny now give you a kickdown switch with the tranny when you get a reman because they had to many returns of burned up trannys. If you would like to bypass it you can by just unpluging the switch and making a jumper wire to connect the two pins but I would not advise it.

stingc · #4 11-14-2004, 10:17 PM

Thanks for the warning. I didn't know it was that easy to burn up these transmissions. Although I didn't plan on leaving a kickdown override on most of the time (especially not on the highway), I do shift the car regularly. From what you're saying, it sounds like that might not be very good for the transmission.

AustinsCE · #5 11-14-2004, 10:27 PM

Would overtightening the throttle cable give the effect, i know the car feels a bunch better when its adjusted as opposed to way loose, but never tightened too much myself.

BENZ TEK · #6 11-15-2004, 01:59 AM

KINDA in a way. Tightning the shift cable will make shift times longer in between gears which mean you will stay in the motors power band longer but that is also depending on if you kept the acceleration steady. If you are pushing on the accelerator while you're under acceleration you will even have a longer shift delay. The best thing to do to be on the safe side is to adjust the cable with only 1/2 mm of play. If you want more power or longer shifts then just keep applying some pedal pressure.

C32AMG · #7 11-16-2004, 08:32 PM

Think of the parallel kick down switch as a power mode switch, when activated it will hold a gear in the engines power band longer. It will also let the transmission down shift to a lower gear sooner and in some models the Trans will start in first gear from a stop. The correct way of installation, is to wire a toggle switch in parallel with the kick down switch under the pedal or use a micro switch with a relay. Turn it on at a stop and off at high way speeds. This performance modification will enhancing the driving performance of you car.

If you have the switch turned on at all times, it is the same as if you had the throttle wide open all the time! Turn the kick down switch off, and on only on when you need it. If you activevate it at highway speed the transmission will down shift.

I have a kick down switch wired in my Porsche 928 and in all of my MB for many years. I know many 928s owners that have made this modification. www.rennlist.com

BENZ TEZ,

I would like to know what was “burned”, on all of these transmissions that the Mercedes rebuilds were seeing because of a stuck KD switch.