77 300D engine turns slow - wont fire up

I own a 1977 300D. I was driving home one day and I noticed when I arrived to Traffic lights the car acted like it wanted to shut off. I resumed driving and as I was getting close to my home, the car shut off. Since then I have replaced the battery, replaced the starter all with no luck. On a fully charged battery the engine turns slow, and acts like it want to start but then dies. Upon a second attemtp at starting, the engine gives me a click, and the engine does not turn! I am super confused. can anyone help?
thank you in advance!

Forums

Diesel Engine Specific Aid

Chassis Model Number

W123

engine turns slow won't fire up

New battery, new starter I'd check the ground cable

Any evidence of mechanical damage

Something could have happened inside your engine to cause to to shut off in the first place. That is what you should focus on first. Could the engine have run low on oil or coolant. Start by getting a big socket on the front crank bolt and see if you can turn the engine over by hand. If it turns over easily by hand then you may still have a starter problem. Where did you get the starter?

Ive always been on top of

Ive always been on top of the lubrication, so Its never run low on oil or coolant. Ive checked all the grounds and all is good. I went to crank the engine again, and now its making a grinding sound. It will turn over slowly and grind for about 2 seconds, then it stops. Feels like it has massive resistance. could this problem be the torque converter gone bad?

Where to start

I would start by removing your valve cover and checking your timing chain and engine timing. Look for loose sprocket on front of camshaft, broken cam, or evidence chain has jumped timing. You may need to turn the engine over by hand to troubleshoot. Go ahead and remove the fan and fan clutch so you can get a big socket on the front of the crank to turn the engine. It is most likely some type of internal engine failure. Kent