Driveshaft won't move with lower unit removed

[suburman]

1983 Mercury OB, 80 HP, S/N 6235449. I removed the lower unit and replaced the impeller. Before I reinstalled it I checked to see if it was in forward. When I put the shift shaft in forward gear. The prop will ratchet when turned clockwise but locks when turned ccw. It does the opposite when put in reverse and spins both ways when in neutral all just like its supposed to. But regardless of what position the shift shaft is in, the drive shaft will not move. I can hold the drive shaft while rotating the prop in one of the locked positions (ccw while in fwd or cw in reverse) and I can feel a direct connection between the drive shaft and the prop shaft but the drive shaft will only rotate about 2 degrees before it locks up. I've rotated the shaft ccw through the 180 degree "low resistance" setting and it will click right into the fwd detent but drive shaft will not move. Same results when I continue to rotate the shift shaft through neutral and reverse. Based on my experience with my 20hp merc I know there's a cam on the bottom of the shaft that can get messed up if you breath on it the wrong way. Is there any way to check the cam without gutting the gear box or is there something else I can try before disassembling everything. I do have the 557 page mercury shop manual that attempts to cover 70+ models in one book and does a pitiful job of it. Any help is appreciated or a reference to where this is supposedly addressed in the manual. Thanks in advance.

 

[QBhoy]

If I’m reading you right here. If you’re meaning the drive shaft that goes into the gearbox (from the engine)…it will be reluctant to move, just with you fighting against the resistance of engine compression of course. The shifting of gear, is only having an affect on the lower unit gearbox. Nothing to do with the drive shaft from the engine running down the mid section to the mating of the gearbox. If you take the spark plugs out…you’ll have a better chance of rotating that by hand, should you need to.
Ignore all of the above if the shaft is still in the lower unit and you don’t mean it is stuck or still in the engine side of things.

 

[jimmbo]

Take the Water Pump Housing off and try turning the Driveshaft

 

[flyingscott]

Put some Vaseline or liquid dish soap on the impeller

 

[suburman]

Thanks for the replies. The lower unit is removed from the boat and clamped in a vice in my shop. That's where all this happened. The drive shaft and water pump are still attached to it (sticking out the top of the gear box). It's not just hard to move its stuck solid except for the slight movement I mentioned above. I recall being able to turn the drive shaft by hand after I replaced the impeller but now its locked. The fact that I feel a hard connection between the drive shaft and the prop shaft tells me there's more holding it frozen than the impeller. I coated the inside of the pump and impeller with light grease before I put it back together and the drive shaft was rotating with little resistance when I turned it with hand pressure. I'll remove the water pump and see what happens. Thanks

 

[Faztbullet]

Did you pull the lower base? If so you may have lost shims and now base is binding the upper bearing.

 

[QBhoy]

Hi. So just to be clear…with the gearbox as it is and separated as you have it. When you manually move the gear selector linkage on the exposed lower unit…into either gear…then turn the prop by hand…the input shaft isn’t moving ? If you’re trying to grip the input shaft and turn just with your hands (when in gear)…there will be a fair resistance from a dry impeller I’d say. Not easy to grip tightly to get enough purchase by hand perhaps. But if you turn the prop by hand (getting more purchase and grip) when it’s in gear…the shaft should rotate too. Is it doing that ? If so…you’re good.

 

[suburman]

QBhoy,flying scott, jimmbo. great minds think alike . I tested the impeller by hand right after I installed it and it rotated fine but something down there tightened up while it sat waiting on parts. I slid the water pump up the shaft and the drive shaft and prop shaft turned in sync for the forward gear rotation. It still wouldn't go into neutral or reverse. While i was in there I decided to check the seal at the top of the shift shaft and when I removed the aluminum nut that holds the seal it pulled up the shaft enough to pull it out of that little cam in the bowels of the gear box. When I started tearing into the gearbox and removing the drive shaft I found that there's at least 1/16" of side play in the drive shaft bearing that sits directly under the pump. Now I'm in the process of getting a bearing kit and new seals for everything. I have a dumb question about the stock mercury illustrations used by crowley marine, PPT, marine engine, and basically every site that sells merc parts. On the parts diagram for the 1983 merc 80HP [ELPT] model 1080623, the "driveshaft gear housing" pic shows the cam (part#46) and the lower reverse locking base (part#45) on top of the shift shaft in the assembly order instead of on the bottom of the shaft. This is the same part numbers and illustrations on virtually any website. Is this a typo or am I missing something. Thanks for all the good advise.