Tach Sender Issue

[Briankinley2004]

Took the boat out fishing this weekend. On the way back in the starboard tach started jumping all over the place but the engine was not. It finally started pegging out then wound up back to zero with no movement and digital hour meter in tach not working. I was able to deduce the issue was on the sender end and not the tach itself by connecting the wire to the port tach with a jumper. I pulled the electrical portion of the sender off and found the tab in the photo below. The tab would rotate with slight resistance in one direction but not in the other. I expected the tab to rotate when I started the engine but it did not move. Is this thing supposed to move when the engine is running? If so what should I look for or plan to replace? I guess I could swap the electrical part with the port side to further eliminate that but if the tab is supposed to turn I know thats the issue. Also the prior owner disconnected the Glendinning cable to install these tachs. The tab in reference comes out so I think it was installed with the tach as the synchronizer cable has a different tab. If I have to replace components on the mechanical side anyway is there a way to connect both the tach and synchronizer to the back of the engine. I cannot remember how my 55C was done

 

[Briankinley2004]

Got the answer to one of my questions today. The prior owner called me about an a/c issue on his boat. I told him about the tach and he said I know exactly what it is. Told me to pull the 90 degree elbow off and it would be the "driveshaft" end. He said it was a weak point in the design and the corners would round off where it went into the engine. Sure enough he was correct. I have two on the way. Now if I can figure out how connect both the synchronizer and tachs

 

[Briankinley2004]

Update in case anyone needs to know in the future. I replaced the drive for the tach and it solved the issue. Also reading up on the synchronizer it appears they can be attached to the synchronizer itself or Glendinning makes a "T" instead of elbow for the back of the engine that allows a tap for the tach drive and synchronizer cable. I plan to try the synchronizer as the old senders are currently attached. It looks like I will need an extension tube for the new ones as they are larger in diameter. I will update if I ever get around to this.