ZF IRM 220 A-1 problem
I have a ZF (Hurth) IRM 220 A-1. On 2 occasions, when dawdling for an hour or so, (in and out of forward and reverse gear) while waiting to lock through, my port gear stops engaging in reverse (it still goes into forward). On the first occasion I took the boat to the yard. The following day, they tried to duplicate the problem without success. More recently while returning from a trip and again dawdling for about an hour, it quit engaging in reverse. I motored to my marina on both engines which takes about 1/2 hour. Just before turning into my fairway, I gave the port reverse another try--and it engaged. I have since tested it in the slip on one occasion and it is engaging. The gear does not make any unusual noises, and in general goes into and out of both forward and reverse gears with a gentle "thunk". I have pressure gauges, and when engaged in either direction, there is a momentary drop in pressure and then pressure resumes. During the 2 episodes, the pressure did not drop when I shifted into reverse. The manual briefly only gives trouble shooting for the gear not engaging at all. Thoughts?