ZF V Drive not engaging at idle

[mquiet]

Boat is a 2000 340 with 7.4l gassers. I noticed after a 3 hour cruise that my starboard drive was not engaging during docking at idle. If I bumped the throttle it would engage in rear. I'm heading down to the boat in a week, but wanted got get some ideas on possible causes and solutions before my arrival. I can tell you that my ATF fluid was full, but has not been replaced in a couple years. Thoughts would be great.


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[MasterFab]

These transmissions engage when internal fluid pressure is directed to either the forward or reverse clutch drums. In order for that to happen, you need fluid pressure. This pressure is created by the oil pump inside the transmission, and should exist whenever the engine is running - the transmission input shaft drives the pump. So, if your fluid level is good, the first possibility is that you have a failing pump. However, this is a relatively rare failure, so I doubt it. A pressure test could indicate the pump state of health.

You did mention that the transmission did not engage after a 3 hour run, and that you haven't changed the fluid in quite some time. Transmission fluids have anti-foaming additives that prevent fluid aeration, and this may be what's happening to you. You have old fluid that was foaming due to your 3 hour run. Then, when when you get to the dock, and the engine is at idle speed, the pump can't create sufficient pressure due to the foaming, and the transmission only engages when you bump up the RPM. The solution here is a fluid exchange and filter inspection. You need to take a careful look at the filter, and see if it is loaded up with metal shavings or debris - this is also a clue as to what is happening.

A third possibility is that your transmission clutch packs are simply worn out, and the transmission needs to be rebuilt or replaced. The clutches do eventually wear out, but usually not forward and reverse at the same time, since they are used differently. So, if the problem is identical in both forward and reverse, this is likely not the issue. Your post does not indicate if this is happening in both directions, so I can't say for sure.

Another thing to check is the shift linkage. Make sure the transmission selector valve, which is connected to the other end of the cable by a small lever arm, is traveling to the full forward and reverse positions when you move the shifter. Cables wear out over time, people step on the linkages while performing service, etc. Something may have happened here.

These are the simple diagnostics - do these first, and let us know.

Dale

 

[mquiet]

Thanks Dale. I will let you know.


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