1971 135 hp inline 6 Mercury lower unit trouble

[buddhapi]

last summer I gave up on a customers 1971 1350 lower unit. it'll work for 1 or 2 shifts, and after that it's like neutral. almost like something in the lower unit skips over, and no longer works right. I wanted some ideas before he brings it back in a couple weeks. I had this lower unit off and back on again at least a dozen times, and it doesn't matter if I assemble it in forward, reverse or neutral.

 

[racerone]

Did you take the lower unit apart ?----Was there any water in this lower unit?----The clutch dog is spring loaded and the spring rarely fails to move the clutch dog into forward.----With the lower unit off does it shift repeatedly ?----Is spline in crankshaft in good condition ?

 

[merc850]

It could be the upper shift shaft (in the driveshaft housing) is is corroded and bends while shifting (happened to me); maybe someone was shifting it into reverse while the engine wasn't running and twisted the shiftshaft internally or..the reverse lock cam is out of phase....the reverse lock assembly is seized..... the shift cable or control box is slipping. [A 1971 control box should be greased by now.]