Shift System Theory:
The shift system of a Mercruiser Alpha system is really very simple BUT it must all be working properly.
The remote control will pull the dash shift cable when placed into forward gear.
The dash shift cable attaches to a shift plate mechanism back on the engine.
The shift plate mechanism will then move the drive shift cable.
The drive shift cable will move a slide mechanism in the bellhousing which in turn will rotate the upper shift lever.
When the shift lever is turned, it rotates the upper, middle and lower shift shafts.
This shift shaft system ends up turning a bellcrank in the lower unit.
The bellcrank will slide a spool assembly which is attached to the clutch.
On the shift plate mechanism up at the engine is a little micro-switch which is called the shift interrupter switch.
Most people call the shift interrupter switch the "kill switch" or "shift switch".
This kill switch is very important! It should never be altered, bent or disabled.
Basically, the kill switch helps the clutch go into the neutral position.
When the driver is pulling back on the remote control, to shift from forward to neutral, a tension will be placed on the drive shift cable.
This tension is a result of the clutch ramps being "locked" into the gear face.
The tension of trying to pull the clutch into neutral will activate the shift plate mechanism and actually stall the engine for a second.
The stalling of the engine will "jumble" the clutch away from the gear and the drive will be in neutral.
More on this later.......
When working properly, the shift will be almost smooth and effortless.
Failures in the shift system do occur......
Typical Failures:
As time puts wear on the shift components, certain failures are bound to happen.
The most common failure symptom is stalling while shifting.
The reason an engine will stall while shifting is because the kill switch is "over-killing".
This doesn't mean the switch is bad!
Stalling is usually due to a stiff drive shift cable or shaft.
The shift system has bushings and seals in certain locations which keep water out of the shift areas.
If any of these seals (or gaskets) fail, then water will seize the components and cause the kill switch to stall the engine.
Another symptom is difficulty in shifting.
If the "kill" system is not operating properly, then the drives wants to stay in gear.
The driver will have to pull hard on the control to get the drive out of gear and
when it finally DOES come out of gear it might pass neutral and slam right into the other gear.
This will cause serious damage.
In either case, shifting problems are not only a nuisance but they can be dangerous as well.
Recommendations:
Have any shift problems repaired before using the boat.
A good Mercruiser tech should be able to diagnose and repair any and all shift problems.
We recommend that the mechanic be Mercruiser Certified and experienced.
The shop should be an authorized Mercruiser Dealer and all parts that they use should
be original Mercruiser made. Aftermarket parts are NOT recommended!
Cable Replacement:
Before we start. This can be difficult and sometimes next to impossible to do if you have no experience.
The service manuals are vague and having a good friend with the right tools to help would be great.
Place the control in forward gear.
The drive (and it's shift shafts) MUST be in forward gear to remove the drive.
Note: A counter-rotation drive (left hand turning prop) must be in reverse.
Remove the trim cylinders and let them hang.
Remove the six nuts that hold the drive to the bellhousing.
Lift the drive a little and let it drop to break it free and assist in removing it.
Careful! The drive is heavy and you might screw up your back!
Now, I made that sound simple but in many cases the drive can be stuck on.
Lifting the drive higher and dropping it a little harder each time might help.
If it's really stuck, then a series of chisels carefully and gently wedged between the drive and the bellhousing might help.
Sometimes removing a drive is just like work!
Now that the drive is off and out of the way, you can inspect the bellhousing area.
Was there water in the U-joint bellows?
Is the u-joint assembly rusted?
Reach into the large hole and try to turn the gimbal bearing.
It's center should turn easily and smooth. If it's loose or stuck then replace it! (another story)
You will also be able to view the "shift cable cavity" where the shift slide is protruding.
This cavity should be free of ANY corrosion and water.
The lever should be in good condition and the roller should spin free.
Most of the shift components in the shift cavity should be greased and clean.
Here is where you get your exercise, climb back into the boat AGAIN.....
Disconnect the drive shift cable from the shift plate.
Remove the two little itsy bitsy set screws from the sides of the end of the drive shift cable.
Remove the black plastic cable end and loosen the brass lock-nut on the stainless tube.
Unscrew the stainless tube from the end of the cable sheath.
Now, this is important!..... slide your hand down the cable sheath as far as you possibly can.
SOMETIMES you will feel a plastic spiral wrap on the cable sheath.
This spiral wrap is to protect the cable from melting against the exhaust pipe.
You MUST REMOVE the plastic spiral wrap or you will live a "hell" trying to get the cable out.
More exercise....... climb back out of the boat......
Wait! You forgot to turn the steering to the left....
Climb back into the boat and turn the steering to the left. (sorry about that)
Climb BACK out of the boat again and look at the shift cable bellows.
You MAY have one of several types of small clamps on the small end of the shift bellows. Remove whatever it is.
Now, grab the gray slide and pull the cable core out of the cable from behind.
Pick up your special 9/16" socket and........ oh..... I didn't tell you about the special 9/16" socket that you must have?
To remove and install the shift cable sheath, you will need an extra deep 9/16" socket which has been turned down to have thin walls.
Snap-On tools sells a great extra deep 9/16" socket but it will absolutely NOT WORK unless you have the walls thinned.
Take the $72.00 socket to a machine shop and have them turn it on a lathe so it will fit perfectly
into the bellhousing as so it will fit straight on the cable nut without binding on the side of the cavity.
IF you attempt to install the new cable without this tool OR if the tool is not milled correctly, then you will destroy your new shift cable during installation
AND you might destroy your $300.00 bellhousing as well.
Mercruiser does NOT sell this tool.
OK, now that you have the correct socket, go ahead and unthread the cable sheath from the bellhousing.
After it's all the way unthreaded, pull on the cable and it should slide right out.
IF it pulls out almost all the way but then gets stuck... it's because you weren't paying attention
when I told you to remove the spiral wrap from the sheath inside the engine compartment.
Good luck if it's stuck. You will just have to spend the next few hours trying to get it free.
Now that you smart people have the sheath out, you need to inspect the shift cable bellows as this is the only time
that you can replace the bellows. If needed, remove the old cable bellows and install a new one.
Make sure you clean the aluminum where the bellows seat. Also, you need to apply Bellows Adhesive to the inside of the bellows.
Get a small but good screwdriver and remove the little stainless set screw that is holding the shift lever in place.
Sometimes this screw is just plain stuck or stripped and you need to take a chisel and crack the aluminum lever in two.
Note: Sometimes it's better to just destroy stuff and replace it then to spend an hour trying to remove a $14.00 part.
Slide the stainless shift shaft down and out.
Now, below that lever SHOULD be a white plastic washer. Remember that!
If you forget that washer when you reassemble then it won't shift right.
Ya' know where that little stainless shaft pulled through? Well, if you look, you SHOULD see a small shift shaft seal pressed up in the bellhousing.
This seal could leak water into the shift cable cavity and in most cases this is the reason that your cable failed!!!
ALWAYS replace the shift shaft seal!
Mercruiser changed the seal to a brass barrel shaped bushing which press fits up into the bellhousing
and hangs down in the exhaust passage. It's about the diameter of a quarter and hangs down about one inch.
IF you have the cheesy old style little shift shaft seal, then pop it out and knock out the upper brass bushing as well.
Go to your Mercruiser Dealer and get the new style, dual lipped, brass shift shaft bushing assembly.
When you press the new bushing into place, make sure you sealed it with loc-tight!
So now you have the new shift seal in place. Good job!
Clean up the stainless shift shaft and grease it up.
Note: A word about grease.... Special Lube 101 by Mercury Marine is great.
You can use 101 as the only grease for this entire job BUT Mercruiser recommends that you use a special Spline Grease in the driveshaft splines before installing the drive unit.
Slip the shaft up into place and install your new roller lever and set screw.
Now, think back..... what did you forget?
The white plastic washer!!!! The white plastic washer must be installed before the lever!
Ok...... the shift shaft assembly is now installed and all greased up.
Now we can start on the hard parts.
Open the package for the new Mercruiser cable and separate the sheath from everything.
Take some Perfect Seal or Permatex 2B or good pipe sealer and coat the brass threads on the sheath.
Take some Special lube and coat a little on the other end of the cable to help it slide through the new cable bellows.
Slide the cable end through the bellhousing and work it through the bellows.
This can be a bitch to do.
When you slide the cable through.... it will soon stop and it will hit the back of the engine. This is when you need your friend.
Have him climb into the boat with a long, thin screwdriver and a flashlight.
He will have to look down behind the engine and locate where the cable is coming through.
You can be moving the cable in and out while he is looking to help him see it.
When he sees the cable, he needs to guide it over towards the starboard side of the engine.
This is tough to do the first time or two and it helps to have a thin screwdriver that is REALLY long.
As he pushes the cable to the side, he needs to tell you when to push.
If it's done right, the cable will miss the engine and slide in easily.
DO NOT FORCE, KINK or BEND the cable!!!!!!
If you bent the cable, then it's RUINED.
If you try to straighten the cable and finish the installation you will be upset to find your engine will stall!
Throw out the damaged cable and startover. Trust me on this. I know.... from experience.
Now......... keep your friend in the boat.
Recheck to make sure you put thread sealer on the cable threads.
Have your friend gently pull on the cable while you use your new special 9/16" socket to thread the cable in.
Don't thread the cable all the way!
Leave one thread showing.
Now get the small parts bag that came with the cable and locate the new aluminum slide, the allen set screw, and the small piece of wire.
Take the cable core and slide it into the aluminum slide.
The lead end of the core will be recessed in the slide.
Thread the allen set screw into the slide until it JUST BARELY TOUCHES the lead.
Adjust the allen screw so the slide has no end play BUT will still spin freely on the core.
IF you over tighten the allen screw then the drive wont shift right.
Twist the little wire piece to lock the allen in place.
Slide the cable core slowly and carefully into the sheath from behind.
If you kink the core then throw it out and buy a whole new cable assembly.
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