Diesel Tach Drive Issue

[Jeremy L]

I have a 1967 MM G1000 Vista (diesel) that's tach intermittently works. I've replaced the tach cable and the tach and have confirmed that they both work. For whatever reason, the tach cable will turn at times and everything is fine and then for no reason it may just stop working. When I disconnect the tach cable from the drive on the side of the engine it appears that the drive turns (sort of raises up a bit when it does start to turn). The weird thing is that about the same time the tach started acting up, oil started to leak where the tach cable connects to the drive at the side of the engine which we've never experienced before. I am wondering if there is a roll pin or something in the drive that is broke The drive is maybe turning at times based on friction but when there is any resistence it stops?

Any thoughts/suggestions on as to why the tach works at times and doesn't work at other times as well as what might be causing the oil leak would be very much appreicated.

Thanks in advance for your assistance.

 

[vecair]

Well I don't know what your drive looks like but we have a 1964 MM 602D that has a 90 degree gearbox drive. Most drives have a drive adapter pin that can have several different ways of driving the gearbox. Most have a tab but some are square drive as well. Check to see if the tab or square is the correct size or worn out. I am guessing like you friction is making it run. If you do have a tach drive gearbox it will be well worth taking it apart and giving it a good cleaning and greasing as that is what usually takes out the drive adapters over time.

 

[vecair]

Heres a pic of some drive pins