Can this problem be caused by a misaligned shift shaft? If not, what could it be? The cable on the motor moves forward when the throttle is pushed, so that seems okay.
Did you work on the motor recently or has this just cropped up spontaneously?
If you had the lower unit off, it's quite common to have misaligned the shift shaft.
Search the postings using the forum's Search feature and you'll find dozens and dozens of threads on the topic.
Most recommend placing the lower unit and the control box in Neutral when reassembling. You'll have to turn the flywheel clockwise while inserting the lower unit in order to get the driveshaft to engage the crankshaft splines.
I bought the boat used and untested last fall, changed the water pump last week, put the boat in the water this week for the first time and found pushing the throttle gives reverse & pulling gives forward. So I'm not sure if it's the shift shaft or not. I did searches, only to find issues with cables and nothing about the shift shaft causing this type of problem.
Can the shift shaft cause the gears to be switched, is the question to which I seek an answer?
I could see having FWD & Neutral without REV or REV & Neutral without FWD, but having them switched seems odd to me; and really don't want to drop the lower unit again if I don't have to.
The shift cable pulls the shifter arm (mounted to the throttle/shift cable bracket inside the powerhead) forward in forward gear and to the rear in reverse.
First ensure the control box is moving the shift cable in the right direction.
If so, and the gearbox is in Fwd when the shift arm on the motor is all the way to the rear, and in Rev when the shift arm is all the way to the front, you've got the shift shaft "out of time".
It is indeed possible to get it to shift the way you described, if the shift shaft was out-of-position when the lower unit was bolted up.
The easiest way to make sure that the shift shaft is correctly positioned when you reinstall the lower unit is to shift the lower unit to Neutral with the control box also in Neutral. Since the shift cam rests on a detent in Neutral, it's positively located and stays in position better.
You'll have to turn the flywheel CW when reinstalling the lower unit, to get the driveshaft to engage the crankshaft.
Sorry to say this, BUT..
Looks like someone may have had the lower unit apart, and put it back together with the shift cam upside down..
I would pull the lower, and set it to neutral (prop will spin freely) and you should feel a detent at neutral.
From neutral a little turn clockwise should give you FWD, and counter clockwise should get you REV.
If you DO get FWD and REV like that, then the index was just wrong, set both the control and lower to neutral and put it back together.
However if you get the oposit, then the cam is upside down and the only fix is to take it apart...
I have the shaft and cam from a 90hp in my hands right now, and if the cam was upside down the shift would be reversed..
It won't hurt the drive to run it that way, but not very safe to leave it like that..
Diplost and others, Mercury lower units of his type have two neutrals. If the gearcase is installed with the shift in the "wrong neutral", forward and reverse will be switched.
As Ed has posted, you need to remove the gearcase, put the control into neutral, set the shift rod to the "correct neutral" and then reassemble.
Yes they have 2 neutrals, however there is NO detent in the "wrong" neutral as the shaft is sliding on the back side of the cam.
This is the reason to put it back together in neutral, most lowers won't stay in the wrong neutral on thier own as there is no detent, the clutch spring on the shaft will push it to FWD when you let go of it.
Thats why I explained to him how to check for wrong index first.
yes, but my guess is that if you take it apart in the wrong neutral it will shift to fwd as you remove it, so verify you have the correct neutral with a detent and fwd is CW from that neutral, before you put it back together, don't just rotate the shaft 180 and put it back together.
If you rotate the shift shaft 180 deg from Neutral, you'll be in Fwd. There is no 2nd Neutral.
This is what happens:
for about 270 deg (or whatever it really is), the shift cam lobe is "low" and does not push on the shift plunger (i.e. it's in Fwd gear).
You can rotate the shift shaft all you want within that range of motion and it'll always be in Fwd gear.
Once you rotate the shift shaft CCW enough to 'find' the detent for Neutral but leave it in Fwd, that's the correct position for the shift shaft if you want to reinstall the lower unit in Fwd.
Shifting further CCW causes the next level of the shift shaft to bear on the shift plunger, moving the shift clutch rearwards in the gearcase so that the "dogs" on the shift clutch engage neither forward nor reverse gears.
Shifting even further CCW from the Neutral position brings the shift shaft's highest part of the "ramp" to bear on the shift plunger, forcing the shift clutch into reverse gear. You're now fully into Rev.
Now, you can STILL turn the shift shaft CCW from here, although it's not a good idea.
It's not designed to do this and I expect puts extra wear and tear on the parts. But if you insist, you can start turning CCW on the shaft and ?Guess What? now you're back in Fwd!!! The shift plunger just "fell" off the "ramp" and is back in the "null" position which allows the lower unit to be in Fwd gear.
Don't forget that there's a pretty strong spring in the shift clutch assy, that is always trying to push the clutch into forward gear. If the shift cam isn't pushing on the plunger, this spring keeps the clutch tight against the ramps on the forward gear. This helps prevent jumping out of gear at higher loadings.
Keep on turning CCW and you'll be right back to where you started, just about to shift into Neutral.
Anyway, that's about all there is to it.
Now, if someone flipped the shift cam over, that's another ball game altogether! But you can figure that out by noting which way the shaft is turning to shift.
Anyway, check 'er out and get back to us, this could get curiouser & curiouser...........ed
1984 115 Mercury has switched Forward Reverse
Linear Mode
