TOPIC: How to replace a lower shift shaft

Just in case anybody wants to save these instructions for a future need:

To remove the shift shaft bushing in preparation of removal of the shift shaft itself:

Place the gear case in a vise with the driveshaft exactly vertical – or as close as the old eye-balls will agree. (I pinch the skeg between (2) pieces of cardboard to avoid marking the skeg.)

Place the gear case into the FORWARD GEAR position by rotating the shift shaft clockwise slowly and then,…Continue rotating the shift shaft a smidge more clockwise, until there is no resistance felt in the shift shaft & it will move slightly clock-wise and counter-clockwise.
This released to push of the cam hidden down in the bowels of the gear case – at the bottom end of the shift shaft - on the shift mechanisms in the gear case and will allow the cam to rest in the desired position as you gently lift out the shift shaft in a few minutes.

Now,...build a tool out of a deep socket that will grip into the 2 slots seen in the top surface of the shift shaft bushing assembly.

Then,...Before you apply it,...use a deep socket to set down on the top surface of the shift shaft bushing assembly and smack it stoutly a few times before removing the socket and applying your "new" tool. It should unscrew counter-clockwise just fine if you smacked it hard enough.
note: on an early gear case like a Mark 55, 58, 400, etc simply grab the edges of this shift shaft bushing with vise-grip pliers and turn it c-cw to unthread it.

Caution!!! (I sound like a freakin’ Seloc or Clymer manual)

Be especially careful not to allow the shift shaft to lift up with the bushing assembly.

That would cause a whole new nightmare.

Note: I replace the entire shift shaft bushing assembly. It comes with the new seals and O-ring
and it only costs about $10 more than getting the pieces and having to try and install the
little seals into the old bushing. A real pain. Inspect the shift shaft at the place the seals
ride. It needs to be very smooth and able to "hold" the seal or you will need to replace
the shaft or install a speedi-sleeve.

Once the shift shaft bushing assembly has been removed,…Gently lift out the old shift shaft straight up.

You will see that there is a snap-ring – or possibly – a clip of some other sort found on the shaft of the shift shaft.
Be sure and have one on the new shift shaft before you install it into the gear case.

Slide the new (used, but good) shift shaft down into the hole and on down into the cam in the bottom of the gear case.

Gently rotate the shift shaft as you apply slight down-pressure,…Until the shift shaft’s splines align with the female splines in the cam and the shift shaft drops into place,…Now it is seated in the cam.

Gently rotate the shift shaft counter-clockwise and if you feel the cam gain resistance and actually shifts the gear case into Neutral,…You have done it!!! If not,…Continue rotating the shift shaft as you press down until the shift shaft drops “home.”

Now,…Gently slide the well greased shift shaft bushing assembly down the shift shaft and thread it into the gear case until it becomes tight.

You R dun.


I have also attached a picture of the related components on a Mark 55, 58, 55A, 58A, etc. Other model Mercs may have different external cams and reverse lock related components, but the lower shift shaft and R&R principles are the same through the late '80s in many cases.
Thom

Great tutorial Thom, you're a Prince for sharing (and volunteering) your knowledge with everyone! I need to start printing out (and saving to disc) and cataloging the great info you and others have offered up here.