Shift Shaft

[Tachyon]

I removed my power head from my Mark 35 It came apart easily but I don’t know how to remove the shift shaft from the lower crowding Any advice would be appreciated

 

[Texasmark]

Nobody hit on this so I'll see if I can help.

I'd expect you be talking about removing the lower unit (from the mid section) and uncoupling the shift shaft in the process. The bottom end of Mercury shift shafts, coming down through the mid section, are splined (female) and fit over a splined stub....part of the LU which protrudes down through a splined interface to a flat piece of metal called a shifting cam.

Shifting is accomplished by turning the cam to the desired position. The interconnection point is accessible buy dropping the LU just enough to get in there and make the disconnect. The main caution here is that you grasp the lower shaft stub....sticking up from the lower unit, so that when you remove the mid section rod/shaft containing the female splined shaft adapter, you don't pull the stub up and out of the shifting cam. Doing so usually requires disassembling the LU to get at the shifter cam and put it back in position for reinserting the shift stub......which locks it in position.

If you are attempting to remove the whole shaft, from the top of the midsection with the powerhead removed, I wouldn't do it without first removing the LU as described above. Reason being, you may/probably will, pull the stub up with the midsection part of the shaft (couplings stuck together) and have to tear into the LU to get things reconnected.

 

[Dave_K]

I have a similar question. After replacing the water pump impeller on my 1991 or 92 40 HP Mercury outboard, I'm having trouble with reinstalling the lower unit. Trouble seems to be alignment of the shift shaft splines in the LU with the shaft above. Both the gear selector up top and the LU itself are in neutral. I tried rotating the LU shaft with a wrench and locked it up. A local boat mechanic was kind enough to un-jam it. (said I had "unclocked it) Whether it's this or the drive shaft, I can get everything within an inch and no closer. Any advice appreciated!

 

[Texasmark]

The quasi rectangular cam has a splined hole in one end and on the side of the other end has a sloped area and 3 detents corresponding to the 3 shift positions. Trying to remember....been many years.....if you turn the cam such that the cam follower on the end of the prop shaft pops out of the F or R groove, you have to turn the cam back to re-insert the follower. In one direction you would run up against the blunt (narrow) end of the cam and a dead, abrupt stop. In the other direction, as you are making 300 or so of 360*, the follower tip will contact the smooth side of the cam and as you apply pressure to the shift shaft and turn, you force the follower (against the spring pushing on it in the prop shaft....moderate pressure to overcome) to move on up the side of the cam and continuing to turn, the tip of the cam follower finally falls in the F gear detent. Then continuing in that same direction another 10ish degrees and you slide into the N detent, and another and slide into the R detent, having the spring compressed the most.

Without the engine running, you probably will have to turn the prop with your hand as you continue to twist the shift shaft in an attempt to get the follower in the R slot in the cam. The cog-slot arrangement of R gear and the clutch dog (that actually does the shifting) have vertical sides and you need to be right on for complete engagement.

Is this what you were looking for?

 

[The Force power]

I have a similar question. After replacing the water pump impeller on my 1991 or 92 40 HP Mercury outboard, I'm having trouble with reinstalling the lower unit. Trouble seems to be alignment of the shift shaft splines in the LU with the shaft above. Both the gear selector up top and the LU itself are in neutral. I tried rotating the LU shaft with a wrench and locked it up. A local boat mechanic was kind enough to un-jam it. (said I had "unclocked it) Whether it's this or the drive shaft, I can get everything within an inch and no closer. Any advice appreciated!

PLEASE READ THE RULES FIRST;

https://forums.iboats.com/forum/foru...ules-attention

 

[Dave_K]

Sorry for posting in the wrong place. Thanks very much to whoever said turn the flywheel. Success!

 

[Texasmark]

Sorry for posting in the wrong place. Thanks very much to whoever said turn the flywheel. Success!

Well the problem wasn't the cam, it was the fact that you didn't have the cogs and slots lined up for R gear and turning the flywheel did that.....while you were putting slight pressure on the shifter. And yes you hijacked this thread.....but your were close in staying on topic at least.