|Outdrive Shift System (MerCruiser)|
One of the most common outdrive operational questions is about shifting problems. Problems with the shift system are a cause of accidents. The following is a synopsis of everything a Surveyor needs to know about the MerCruiser outdrive shift system.
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.
Lost yet? Actually, it's not too bad!
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.
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.
Have any shift problems repaired before using the boat.
A good MerCruiser Certified and experienced tech should be able to diagnose and repair any and all shift problems. The shop should be an authorized MerCruiser Dealer and all parts they use should
be original MerCruiser made. Aftermarket parts are not recommended!
Now, that being said, the following is a step-by-step guide of how to do it yourself! This guide should assist you in estimate review for this procedure.
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
- 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 holding 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 it 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 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 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. (The docket tool for removing the shift cable can be ordered from www.sterndrives.com. Order #91-12037 for $26.55. If you attempt to install the new cable without this tool or if the tool is not milled correctly, 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.)
- Okay, now that you have the correct socket, go ahead and unthread the cable sheath from the
- 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 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.
Maybe I just got a little ahead of myself... Let's try to stick to removing things first.
- Get a small but good screwdriver and remove the little stainless set screw holding the
shift lever in place. Sometimes this screw is just plain stuck or stripped and you need to take a chiesel 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 the washer when you reassemble then it won't shift right.
Cool! Everything is in pieces!
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 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 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. Hopefully he isn't to drunk from drinking beer as he was watching you do all the other work.
- 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 stb. 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 start over. Trust me on this. I know...from experience.
Now...keep your drunk friend in the boat. Just keep him happy with another beer or
- 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. Do not grease the core! If you grease the core then it will stall the engine when you shift.
Time for some exercise. Your friend is too drunk so climb in the boat with the other small pieces that came with the cable. You will also need a 7/16" open end wrench, an adjustable wrench, lock pliers, a new small
cotter pin and a beer for the drunk guy.
- Thread the stainless tube into the end of the cable all the way and then back it off two turns.
- Lock it down with the 7/16" nut.
- Now slip the little anchor thing into the plastic tube and slip it over the end of the core.
- Install and tighten the little, little set screws.
- Take the spiral wrap and install it on the sheath down low where the cable gets close to the exhaust pipe.
- With the control in forward, install, temporarily, the cable to the shaft plate mechanism. This will help hold the slide and shift shaft in the forward position for installing the drive.
- Exercise time...jump out of the boat and make sure you have cleaned off all the old gasket material from both the drive AND the bellhousing.
- Glue (with bellows adhesive) the new water passage o-ring and the large u-joint hole o-ring into place.
- Place the new drive gasket on the studs of the bellhousing.
Get this...use no sealer. That's right. It kills us MerCruiser mechanics when we see Silicone sealant squishing out from the drive gasket. It's not right. Don't use sealer!
- Take some 101 grease and put some on the drive mounting studs and on the large o-ring.
Let's inspect the drive before we install it. Do the splines look clean? Have you greased the cross bearings? Take a good look at the lower shift shaft and make sure in moves free. Take some MerCruiser Spline grease and grease up the splined shaft.
Before the drive is installed, think...is it time for a new water pump? Is the drive ready to be resealed?
Does your drunk friend happen to have an engine alignment tool? The engine alignment should always be tested before the drive is reinstalled. Always.
The MerCruiser tool is #91-5475A1.
Now your ready to install the drive. Your drunk friend might be able to help you.
- First place the drive into forward gear. To do this, turn the little shift shaft clockwise
as viewed from the top. While turning the little shaft clockwise, turn the prop
counterclockwise until it locks. The drive must be in full forward before and during installation.
- If the drive comes out of forward while you are struggling with it, then stop and put it back into forward.
- If the drunk guy accidentally bumps the prop, then recheck to make sure it's in forward. Also, make sure the little bellhousing shift lever roller is in the fork of the slide!
All of this has to be perfect before installing the drive. If one thing is out of place then your screwed.
- Have the drunk one lift the drive in place while you guide the splined shaft though the hole. It will go "so far" and then stop.
- You now need to rotate the prop in the reverse direction to turn the drive to line up the splines. Note! If you turn the prop in the "ratcheting" direction then it will pop out of gear! Remember, it must be in forward to be installed.
- When the splines get aligned, the drive should slide on more. Every so often a drive will slip right on and you will be done. Most often, the drive will stop just a little short of all the way. If the drive has stopped and seems stuck from going all the way on, you need to check something. You need to confirm the shift shafts are in the proper positions. If you force the drive on and the shafts are wrong OR the roller is not in the slide right then damage will occur. After you are positive the shafts are correct...then a good kick can help. I like to "bump" the drive on gently with a soft log. Theoretically, if the splines are in good condition, and the engine is aligned, and the shafts are aligned, and the splined shaft is in good condition...then the drive will slide on easy. Not always the case. Be suspicious if the drive is hard to install. Get one of the nuts tightened in place to hold the drive and let the drunk guy rest.
At this point, you have the drive mated up nice but the shift cable is not properly adjusted
yet. What you need to do, is confirm a few things. Did you rip the gasket during the installation? Did you lose any o-rings? Did the roller stay in the slide?
Have your drunk friend climb back into the boat to test the shift.
Have him remove the drive cable and push the end in all the way while you turn the prop. It should lock in one direction and ratchet in the other. Then have him pull the end out a little till you get neutral.
If you get a smooth neutral then have him pull the cable out for a reverse test. With the cable pulled out... rotate the prop again. It should lock in one direction and ratchet in the other.
If you find it's not shifting as above, then remove the drive and check it again. Practice makes perfect.
If you are right on the money, then install the rest of the drive nuts and cylinders.
- Remove the dash cable from the shift plate.
- Adjust the stud in the slot to the bottom of the slot.
- Push the drive cable inwards while someone locks the prop.
- It is VERY important to make sure the prop is fully locked.
- Measure the drive cable so you have a 6" distance between the hole at the end and the brass barrel. (center to center!)
- Adjust the brass barrel so it measures 6" center to center. Don't move it! I sure hope the prop was locked in forward (the reverse direction).
- Place the drive cable onto the shift plate assembly being careful not to move your 6" adjustment! Now you have the drive in forward AND the shift plate is in forward too!
- Adjust the plastic barrel on the dash cable to match the plate studs so the cable will go right on without moving the shift plate or the drive cable.
- Install the nuts and the cotter pins.
You can now do a static shift test.
- Place the control in forward. The prop should lock in one direction and ratchet in the other.
- Take a notice of the ratchet tension.
- Now go into neutral. The prop should turn both ways free and no noise should be heard.
- Shift into reverse and feel the ratchet tension. Also make sure you get a good "lock" in the
- If the reverse is weak in the ratcheting, then adjust the stud in the lever slide on the shift
The final test is how it shifts in the water! Just go out and have some fun. IF you need to adjust the shift, only adjust the dash cable barrel.
The above is excerpted from www.sterndrives.com.