91 Mercury 150 XR4 lower unit stuck in forward gear

Toxarch · #1 September 24th, 2009, 04:51 PM

When I was reinstalling the lower unit the other day, the drive shaft splines weren't lining up properly for reinstallation. So I put the lower unit in reverse (using the driver's seat shifter) so that I could turn the prop and line up the drive shaft splines properly. It worked and I got the lower unit reinstalled. But I later found out, not correctly.

Well, I took it out on the lake the other day and found that the lower unit is now stuck in drive; no neutral and no reverse. So I dropped the lower unit again and messed around with the shift shaft to try to get it into neutral. It doesn't seem to want to go into neutral with me turning the shift shaft by hand. I marked it with a black marker and found the limits of the rotation and tries the middle and everything between the limits while turning the drive shaft by hand. Am I missing some step? When using the shifter at the driver's seat, it appears that the upper unit shift shaft barely turns between drive, neutral, and reverse.

Any tips to get the lower unit back to neutral so I can install the lower unit back correctly? This didn't happen the last time I dropped the lower unit.

Jeff_G · #2 September 24th, 2009, 05:17 PM

The shift cam is probably turned wrong in the lower unit. Try to turn the shift shaft back to forward then neutral. You are probably out about 1/3 of a turn. While shifting turn the prop shaft so the clutch and gears don't high center on the ears of the gears.

Toxarch · #3 September 24th, 2009, 05:48 PM

I tried turning the drive shaft back and forth by hand while turning the shift shaft with the other hand. The shift shaft appears to have about 200 degrees of rotation. I cant not seem to get it into neutral. I thought maybe there was something I was missing. Does the 200 degrees of rotation sound wrong? Or is it getting stuck before it goes into neutral?

When shifting using the driver's controls and measuring the rotation of the upper shift shaft, it doesn't appear to turn much at all.

CharlieB · #4 September 24th, 2009, 07:46 PM

The shift cam in the LU is a simple one way ramp with two small notches, one indicates Neutral, the other indicates Reverse. Turning the shaft too far and the follower falls down the backside of the ramp (Yes, you can turn the shaft 360 degrees,but it is tough to turn with bare fingers)

Using pliers firmly hold the shaft and try turning, one direction you will feel the ramp, the other you will feel major resistance, rotate and feel carefully for an indent, the shaft should set into that position, Neutral, continue turning and 'set' into the next detent which will be Reverse. Reasseble the LU to the motor.

Toxarch · #5 September 24th, 2009, 07:49 PM

I tried turning the prop to relieve the tension on the shift shaft. The shift shaft turns easily when this is done. Now looks like there's about 250 degrees of rotation in the lower unit shift shaft. I still can't seem to figure out how to get it into neutral. The prop should rotate freely when in neutral, right?

Toxarch · #6 September 24th, 2009, 08:55 PM

Thanks for the replies. The key was that I HAD to use pliers. Not being sure about what I was doing was the problem. I turned the shift shaft by hand CCW until it stopped, then used a pair of channel locks to get it that last bit to where the detent caught and put it in neutral.

After that, had trouble with the lower shift shaft lining up with the upper shift shaft. Took the motor cover off, disconnected the shift cable, got the shafts to line up and then reassembled everything.

Thanks again for the help.