1987 300SDL shifting problems
 

So my 300SDL has some shifting issues, but not at all times. It happens randomly and usually when it happens is out of first gear. Also what I have noticed is that the brake light will flicker on and off when this happens. I tried checking the kickdown switch but could not see anything. I did not try to remove the plastic covers under the steering wheel, but will do so later tonight. I checked the e brake and it is not loose when the brake light it flickering. If there anything else that could be going on?

your brake light is probobly not connected, if it's the red colored brake light, there's a sensor/switch that senses that could be broken. most likely it's a ground, if it's that wear sensor it's either a ground or a wear sensor making contact and you'll need brakes soon. when you say shifting issues... Is it a flair, slamming into gear, taking it's sweet time etc?

It will not shift out of first gear when it has the problems.

If it could not shift out of 1st then it could be a worn B2 piston. I talked with BoiseBenz before and he is very knowledge on the SDL tranny. I remember he told me that you can buy a 'over-sized' B2 piston to take up the slack. PM him.

Good luck.

A continuous failure to upshift can point to governor clogging, or valve-body troubles. Intermittent is often electrical (kickdown).

B2 typically causes failure to move forward at all, that is, to shift INTO first gear. Failure to upshift is mostly caused by kickdown system issues: stuck switch (in cabin, under skinny pedal), sticking solenoid (right rear corner at bottom of transmission). You can easily isolate the switch by pulling the relevant fuse ("AT kickdown solenoid). May be 5 or 8? Pulling the fuse does NOT isolate and prove the solenoid itself to be good; it can still act wonky mechanically with no power being supplied. The solenoid can be serviced from under the car, without even removing the pan.

Your flickering brake light (whether it's the e-brake or the "low fluid"/"bad pads" light) is wholly unrelated; there is no CAN bus or other trickery on these cars. Unless the harness has shorted together somewhere. But I don't know if the wires even get physically close anywhere to allow that to happen.