Shifting Problems

[searay398]

I have reviewed some of the previous posts on this topic but my problem seems slightly different although it may be the same and I am just to green to realize it.

The engine stalls off when I shift into reverse. This is my test run after replacing shift and throttle cables and the control unit. Without the engine running if I shift into forward and spin the prop by hand it will ratchet clockwise. In neutral the prop spins free. In reverse the prop will rathet counter clockwise. With the engine running it will start in neutral. I have throttle control if I depress the button to keep it out of gear and operate the throttle. With the engine running when I shift to forward the prop spins but when I shift to reverse STALL!!. At first I was only trying reverse and thought that it may have been the neutral kill switch wiring but shifting to forward ruled that out.

Two more things to note. When shifting to reverse there seems to be a little more friction on the controls which I kind of wrote off as just being a different control box before trying with the engine running but now this may be related or a symptom of something else. The other thing is that in reverse while spinning the prop by hand it takes more effort to rotate through the ratchets than it does in forward. I did not spin the prop prior to changing the cables and box so I have nothing to compare to other than forward.


Thanks for the help

 

[Don S]

Re: Shifting Problems

What are we working on? I have to assume it's a Mercruiser.
If So, then the cable is out of adjustment.

 

[full stringer]

Re: Shifting Problems

agreed bad adjustment shouldn't rachet in gear its only supposed to ratchet the opposite direction if in forward and likewise in reverse but when in gear it's solid

 

[searay398]

Re: Shifting Problems

Yea it is a Mercruiser Alpha One. Thanks for the quick replies. After your reply I did some further investigating and I believe that you guys are exactly right. I found a great article posted by another user on this just incase anyone else has this problem in the future, I will paste it on the bottom of this post. I will hopefully make the repair in the morning. Thanks again.


Post I found
Mercruiser MC-1, R, MR, Alpha One, Gen II shift system

Many people ask about the shift cable setup and the shift cutout switch. Here is an explanation of how it all works and how to set them up. This will assume that there are no ongoing problems, like stiff cables or excess slack in the shift system.

Theory of operation
(Courtesy of "Qystan")
The shift cutout switch "can" work in both going into gear and out. Let me explain.

If you study the intermediate shift plate and the linkage. The function it performs is for the upper shift cable to move the lower (both directions) and allow one to move independently of the other. When independent movements occur, the shift cutout switch will sense this and cause the ignition to be cutoff, ignition is restored when the cables synchronize.

So how does this work? The gear design allows shifting into gear quite easily, hence engaging gears is usually not a problem and the 2 cable movements stay synchronized during the engagement cycle, the switch is never actuated. If you have a sticky lower cable, the upper cable movement will result in an out of sync situation if the lower cable does not move. The switch will be actuated and kills the engine.
Shifting out is slightly different, due to the gear undercut, the gears do not disengage easily. This will always result in non-movement of the lower cable and actuating the switch. When the engine 'dies' the torque on the gears which holds them together is removed, allowing the gears to disengage. In disengaging, the lower cable moves and synchronizes with the upper cable, resets the switch, restores ignition.

Bad cable adjustments which misaligns the upper and lower cable neutral position will cause engine dying during engaging shifts. The misalignment gives an upper cable 'overtravel' which the lower cable cannot synchronize due to its limited travel. Symptoms would be engine dying going into gear in one direction but the other is OK.

Adjustment of the cables
1. Remove both the shift cable (to leg) and the control cable (from control box) from the shift plate.
2. Push in on the end of the cable and have someone turn the prop slowly Counter clockwise at the same time. When the prop stops the unit is in Forward gear.
3. Adjust the brass barrel until the distance between the centre line of the brass barrel and the cable end guide mounting hole is EXACTLY 6 inches. (pre-1974, 5-7/8")
4. Re-install the shift cable onto the shift plate. DO NOT change this adjustment again.
5. With the control lever at full throttle in forward adjust the brass barrel to line up with the guides on the plate. DO NOT install the cable at this point.
6. Turn the brass barrel AWAY from the cable end guide 4 turns. Install the cable on the shift plate.
7. Move the control lever to the full reverse position, as the helper turns the prop slowly clockwise until it stops.
8. Check the shift cutout switch roller position. If is has moved from the centre position, adjust the brass barrel on the control cable, one turn at a time (maximum 4 turns) until the roller is in the centre position.
9. Secure the cables with the nyloc nuts. DO NOT tighten them onto the barrels.

Cutout switch
The cutout switch should also be checked. The correct adjustment for the switch is to activate when the switch arm has moved 1/8". Check this with a 1/8" drill and a multimeter. With the key 'OFF' put the multimeter across the switch (points ignitions will have to have the points open for this) and start moving the switch arm. When the meter shows that the switch has closed, check the gap between the switch arm and the actuating lever, it should be 1/8". Bend the arm of the switch to achieve the dimension.