350SDL

As the post title states, my 1991 350SDL will not shift out of first when in D or 2 or 3. It will go into reverse just fine, so it understands forward and reverse.

Up to this point, the transmission has been fine. After looking online, I checked the kickdown switch under the accelerator pedal. I removed it from the vehicle and drove the car without the switch but that didn't change anything (still stuck in first). The kickdown switch is a 2-pin switch. I pushed the switch plunger in and it will not easily pop back out. I lubricated with Kroil and silicone spray and it's a bit better, but still a bit sticky. Funny thing about that switch - I figured it was an open/close switch, and open when the plunger is out. However, I checked the resistance through the switch at the two pins when it was open and closed and got no continuity between pins, regardless of whether the switch plunger is in or out. This makes me to wonder how the kickdown switch on this car operates. Can someone tell me how? Do I simply need a new switch (I may anyway because it's always open). What would happen if I jumped the connector going to the switch?

The car is relatively new to me (~6 months). I have not changed tranny fluid or filter since I've owned it. Tranny fluid looks good and it filled appropriately. PO had a good shop perform maintenance, so I assume that the fluid is pretty new, but not certain - I will check the records.

Any other thoughts on what would cause the transmission to stay in first and not upshift at all?

Thanks.

sliver 126

Check mechanical linkage to shifter for excess play,
Check vac hose to transmission module for leaks and check module on transmission for function.
Check Vacuum pump and any branching in lines.

350SDL

Not to be too annoying, but I am a newbie with this car, and I don't have the pleasure of a manual. On the mechanical link to shifter, do you mean the mechanical linkage to the shift lever in the car or the kickdown cable itself. If the cable, I've looked at that and it does pull forward and spring back, so I assume that is normal.

Regarding the transmission module and vacuum pump, I don't know where these are located. Any further assistance would be appreciated.

Thanks again.

sliver 126

Best thing you can do for yourself if you intend to DIY troubleshoot and repair is invest in the service manual and make sure you have the operator manual for your car.
With these manuals , some tools and a little aptitude.
You can save yourself thousands of dollars over the life of the car,
The shifter arms that bend, cease or wear are up under the car beside the transmission.
Go under and get someone to sit inside and gently shift back and forth.
You will see if separated or stuck.
Failing that get the help away from the shifter and see if there is excessive play in the linkage. You may need new bushings.
Failing that check vacuum hose coming from transmission module and module itself for leaks and function.
There may be wires going in to check them for corrosion, breaks or shorts.
Air pump is on engine toward front. Follow the hoses. This sometimes fails.
GET the MANUALS.

350SDL

Sliver 126,

I appreciate the info. I'm not a mechanic, but I've done my fair share with car, truck and boat engines, so I can manage most repairs or know when I can't. That said, all I've done to this car is brakes & rotors, fuel and oil filters, t-stat, and mono-valve replacement, so still learning my way around it.

What is the best service manual and where do you get them?

Any feedback on $15.99 DVDs on EBay -noted as follow? Seems to good to be true? MERCEDES BENZ ALL MODELS SERVICE REPAIR WORKSHOP MANUAL FACTORY DVD/CD GUIDE

Also, I posted above that I did not measure continuity through the kickdown switch regardless of the position. I reran that test, and this time the switch was open when the plunger is out, and the switch is closed when the plunger is open. This makes sense to me, and is the reason that simply disconnecting the switch should help determine whether the switch is bad or not. In my case, the switch is ok. I am posting this just to be clear about the process and results of solving this problem.