Hi all,
I am seeking technical help with a bad om617 4 speed manual transmission on a 1980 w123 300D. The vehicle was purchased from the original owner last September, where it sat in a garage unused for the last decade. It is in very good condition with 195k kms on the clock. I have been putting in hours of love to make her go another 200k.

Initially, it had a dirty fuel system, so I swapped the tank and filters successfully. Next the doors were having trouble closing, so I picked some old replacement strikers and got some plastic eye inserts from China, solved. I adjusted the valves but I believe the timing to be off, still unchecked and unresolved. She has difficulty starting without turning up the throttle on colder days or when she has been sitting. Everything else runs smooth and she had been until yesterday...


THE PROBLEM ---- After driving for about an hour, I attempted to make a U turn on a tiny street. Upon shifting into reverse to maneuver back onto the pavement and climb a 10cm dropoff onto the shoulder, transmission took a poop. I continued reversing with the momentum of the car and was unable to shift into any gear. Luckily, the car moved forward with gravity to a stop on the edge of the pavement and not blocking traffic. It could have easily died intersecting the road!

When the car is off I can shift into all gears with a jerky movement into position. When the car is on, I cannot move the stick from N into any gear. Its like there is less pressure in the clutch when the car is on with the engine running. Overall, the clutch is more spongy when engaging. The engine runs fine. I can start the car in gear with clutch pressed in but the sounds is a terrible grinding. Sometimes when I go from on and off and engaging gears to not, then the shifter can get stuck in N even when the car is off.
One of the maintenance points I have neglected was servicing the trans oil. I have not even checked the level. It has been jumpy, skippy in second gear over 40kph. The shifter sometimes is ¨popped¨ out of second going into third when accelerating with a spring like force. There seems to be some lag in shifting gears and properly working the clutch but I attest that to an old, long gearbox. I can shift out of gear without engaging the clutch.

There are many severe inclines on the Island I live. I constantly need to downshift to first to make it up some steep grades. Even parking at my house requires a high level of parallel-parking-on-an-incline skill.
Right now, she is parked at my house on a flat, steep decline with nose facing downwards. I have plenty of tools and the time to fix it but I cannot move it nor lift it. Even jacking it up would be dangerous.

---> I am hoping it is a bad clutch master cylinder. I have been researching down that path. I am afraid the clutch plate could be bad. I pray its gear box is still in good order.

Any suggestions? Advice? Insults?????
Thanks for reading. Any response is appreciated.