79 rude 140,goes into forward gear great,tried adjusting the cable,goes into reverse good on the trailer,in the water it trys to go in but never catches,just keeps clattering,I have had the lower unit off to replace the water inlet screen and water pump, I heard that the shift rod has to be measured to adjust length,is this correct? dropping the gears is the last thing I want to do.I had the boat 10 years this is the first time I had it in the water so I don't know how reverse was before. want to cover other bases first before tearing gears apart for inspection.