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Replacing Your Trim Limit and Trim Position Senders

Replacing your R, MR and Alpha One Trim Limit and Trim Sender Switches

Purchase your Trim Limit and Trim Position Sender Switch Kits HERE.

Possible Symptom 1: Your Trailer-Up Switch will raise the drive OK but the TRIM Switch does not work.
Possible Symptom 2: Your Trim gauge does not work.
Fix: Replace the Trim Limit and Trim Sender Switch's.

Theory of Operation:
The Trim Limit Switch is a safety device which keeps the driver from over-trimming while under way.
Trimming the drive too high while under way can cause damage, injury or death.
The Trim Sender Switch is used to send a signal to the Trim Gauge so you can see the level of the drive.

The Trim Senders are located on either side of the Gimbal Ring.
The Trim Limit Switch is mounted to the Port side of the Gimbal Ring.
Newer model switches will have a "TL" or "Trim Limit" embossed in the plastic (see image below)

The Trim Sender Switch is on the Starboard side of the Gimbal Ring.
The newer model Trim Sender switches have a "TP' or "Trim Position" embossed in the plastic(see image below).

Each switch has a wire harness that is routed behind the Bell Housing after which it passes through
a small hole in the Gimbal Housing shroud and into the bilge.
The wires look like black lamp chords.
It is these wires and how they are installed which makes replacement of the switches difficult.
Partial disassembly of the Gimbal Housing is required to replace the switches and wires.
You must always replace the wires with the switches. Never just replace the switch.
The wires absorb water which leaks up the core of the wire to the switch.
If you simply replace the switch it will not work or it will go bad in just a short while.

The switches are sold in a Trim Limit/ Trim Sender Switch Kit which includes both switches.
The wires are included in the Kit and they are soldered and sealed in place at the factory.
You can not buy just one switch. You can only buy the pair of switches in the Kit.

After the wires pass into the boat from the outside they go to two different places.

The Trim Limit wires will have a blue and a purple sleeve near the bullet connector on the end of the wires.
These Trim Limit wires usually run over towards the Trim Pump Assembly and they butt into the Trim Wire Harness near the Trim Pump.
This allows the switch to "break" the trim-up circuit as the drive is raised to a certain height.

The Trim Sender wires may not have any color sleeve or if they do, one side will have a brown sleeve.
Most motor wire harnesses have a Brown Wire with a White Stripe.
This Brown/White wire leads up the dash and fastens to the Sender Terminal on the back side of the Trim Gauge.
The wires from the Trim Sender switch plug into this Brown/White wire and a ground.
Older engines have a small screw-style terminal block to which these wires would fasten using the little bullet-to-ring connector
pigtails that are included in the trim Switch Kit.
The Brown/White wire runs to the trim gauge while the second wire fastens to a ground terminal screw.

Replacing the Switches:
Replacing the switches is no easy task.
Alpha One customers will need a Hinge Pin tool.
Alpha Gen II and Bravo customers will also need a Bellows Sleeve Installation tool.
Bravo customers will also need a Tappered Insert Tool # 91-43579
We also suggest that you purchase a Factory Shop Manual.

Tilt the drive up and remove the clamp from the rear end of the exhaust bellows.
Pull the exhaust bellows off of the Bell Housing.
NOTE: Installation of the exhaust bellows requires the use of a special tool.
Sometimes old exhaust bellows can be reinstalled without the tool. If the bellows can not be fitted back into place, you will need a Bellows Expansion Tool.
You can also buy an Exhaust Cuff/Tube and install it in place of Exhaust Bellows.
The Exhaust Cuff/Tube does not require the Expander Tool.

Turn the steering to one side so you can access the switch retainer screws.
Take a phillips head screwdriver and remove the two retainer screws from the first switch.
Pull the switch away from the Gimbal Ring and tie it up out of the way.
If you don't tie the switch up out of the way it will get caught between the shroud
and the gimbal ring when you try to turn the steering to the other side.
Use your Hinge Pin Tool and remove the threaded hinge pin.

Turn the steering to the other side and remove the other switch.
Remove the second Hinge Pin.

For Alpha One: Use a 5/16" swivel socket (1/4" drive) on the end of a very long extension
and loosen the Ujoint Bellows Clamps at both ends of the Ujoint Bellows.
The Bellows are glued into place with Bellows Adhesive so it will take some force to pull them free
while you separate the bellows from the housings using a dull screwdriver to break the seal.
For Alpha gen II and Bravo: Pull out the aluminum sleeve which is locking the
bellows into place in the Bell Housing.
Collapse the end of the bellows after the sleeve is removed and push it through.
Bravo Customers will need to use the Tappered Insert tool to remove the plastic tappered insert
which is locking the water hose into place in the Bell Housing.
NOTE: This is a great time to replace your Ujoint Bellows.
If you think that you might have damaged the ujoint bellows during removal, replace them.
Never install damaged ujoint bellows.

You should now be able to pull the Bell Housing far enough away to loosen the rear water hose clamp.
Careful..... twisting and maneuvering the Bell Housing can ruin the delicate shift cable.
We recommend replacing the shift cable whenever this type of repair is being done.
Read more about shift cables at Replacing your Mercruiser Alpha or Bravo Shift Cable.
Read more about replacing your Gimbal bearing and Ujoint Bellows at Replacing your Gimbal Bearing and Ujoint Bellows.
The water hose clamp is difficult to access as it is tucked way up near the Bell Housing.
Chances are pretty good you are going to ruin the water hose so we advise buying a new water hose.
With the hose disconnected from the Bell Housing you should be able to pull out the shift cable and let
the Bell Housing Assembly hang out of the way.

You will now be able to see where the trim wires go.
There is a small retainer plate holding and sealing the trim wires in place as they pass into the boat.
This plate is held in place with either one or two small bolts.
Newer Alpha Gen II's and Bravo's only have one bolt and this makes life much easier.
The top retainer plate bolt is very difficult to access on the Alpha One.
Mercruiser techs usually bend an open ended 7/16" wrench into an offset "S" shape.
Removing the top screw without a customized wrench is near impossible.
NOTE: These screws might be corroded in place. Use patience and take your time removing the screws
being careful not to snap them off.
After both screws are removed you can remove the retainer plate and set it aside.

Hop up into the boat and locate the wires inside the bilge.
Make a note as to how the wires are routed and hooked up.
Disconnect the wires and pull them out from behind the boat.

Installing the new senders is the reverse of removal.
Goo the threads of the retainer bolt(s) with Perfect Seal so they come out easy next time.
The new trim wires will have grommets molded onto the wires.
When you route the new wires through the hole take notice of how the sealing grommets fit.

Tie both switches up high and out of the way during assembly of the Bell Housing or they will get cracked.
If you have decided to replace the Shift Cable, do that first.
After the Shift Cable is installed go ahead and install the water hose.
Pushing a new water hose on to the tru-gimbal-fitting can be very difficult and frustrating.
We like to coat the inside of the hose with Mercury Power Tune spray or grease.
Make sure the clamp is loose but in place on the hose before pushing the hose onto the fitting.
Push and twist and push and twist and then push and twist a little more.
It has to go on far enough. If not, it will pop off and you will overheat the engine.
Snug up the clamp and then clamp the other end of the hose on the brass fitting in the Bell Housing.
The position of the water hose clamps is important. They must be positioned as so you can access the screw.
Now it's time to glue your u-joint bellows in place.
Do NOT install the bellows without bellows adhesive!

It's important to note how the clamps will be positioned
The bellows will first be installed on the bellhousing. The clamp will face down opposite the side with the water hose.
When we install the bellhousing to the gimbal housing (transom) we will have to have the clamp positioned
with the screw facing down on the stb. side.

Now.... note that the bellows has a "Forward" and "up" at one end.
This means the obvious!

Coat the "rear" end of the bellows (inside) with bellows adhesive and before the glue dries, push the bellows onto the bellhousing.

It should almost "snap" in place when the grooves line up.

Make SURE that they are straight BEFORE the glue dries!

Now, position the clamp and gently snug up to tighten.

The next step will be to coat the other end with bellows adhesive and place the clamp loosely on the bellows.

Make sure the clamp is positioned with the screw facing down on the right!

Push the entire bellhousing assembly up and into place while feeding the the shift cable back through its bellows.
You will have to be feeling inside the hole to assist the bellows into place.
Also, you will have to push the bellhousing WAY IN to "snap" the bellows onto the groove.
While this is taking place, you also have to watch that the clamp has not fallen out of place!

Once you feel that the bellows are fully in place, hold it there for 5 minutes to let the glue set-up.
Now take your 1/4" ratchet set with a long long extension and a swivel 5/16" socket on the end and snug up the clamp.
Inspect carefully to make SURE the clamp is straight and in place.
DON'T over tighten the clamp!!

Now that both clamps are snug, you can get the hinge pins installed.
There should be fiber side washers on either side between the bellhousing and the gimbal ring.
If they look worn, replace them.
Align the washers and the bellhousing up.
Apply a drop of good lock-tight to the hinge pin threads and install the pins.

Torque the hinge pins to 40 lbs.

Usually the Trim Sender Kits include some basic instructions.
Before fitting the switches into position on the hinge pins, take a look at the them.
The center piece rotates. You will see a notch on both the center piece and the housing.
These notches are alignment marks.
Turn the center piece as so the alignment marks are lined up.
With the drive in the FULL DOWN position you will install the switches being careful not to
misalign the marks.
Most of the time this will be the perfect position and the Trim Limit and the Trim Gauge will be right on.
Some minute adjustments may be required to "tweak" the gauge reading and trim limit setting.
Your Shop Manual will describe the exact height for the Trim Limit.
Loosening the retainer screws and rotating the switch housing just a little bit in one direction
or the other will change the settings. Snug up the screws and cycle the drive up and down to confirm your setting.

You will adjust the senders after the drive is mounted.
Grease the hinge pin zirt fittings.

Now it's time to inspect your work.
Look at the clamps again, are they perfect?
Did the bellows seat completely>
Is the water hose kinked?
If you didn't cut the water hose OR if you didn't get it ALL the way on, then it will kink.

It's simple to fix, just redo everything again.

We still have to contend with the exhaust bellows.
This is where you get to use your new exhaust bellows expansion tool!
This tool will pay for itself with just ONE use.
Clamp the exhaust bellows first to the gimbal housing (transom).
You really don't need adhesive for the exhaust.
The clamp should be on the bottom if possible.

Now place the other clamp on the rear end and get them position CLOSE to the installed position.
Work the bellows expansion tool in through the bellhousings exhaust passage and into the bellows.
Expand the tool and place the lock in place.
Pull on the tool to work the bellows up onto the bellhousing.
Now, slide the metal rod pin through the hole in the tool. This allows you to release the tool so you can
tilt the bellhousing up to access the last clamp.

Hey! your practically done!

Finish up by properly installing the drive and go boating.

Change your Alpha Gear Lube
Change your Bravo Gear Lube
Why does my drive lube have white streaks?
Why does my drive lube have gray mush?
Replace Your Alpha One Water Pump
Replace your Alpha Gen II Water Pump
Rebuild your Bravo Raw Water Pump

Troubleshoot & Replace your Alpha Shift Cable
Troubleshoot & Replace your Bravo Shift Cable

Replace your Alpha One Bellows & Gimbal Bearing
Replace your Alpha Gen II Bellows & Gimbal bearing
Replace your Bravo Bellows & Gimbal Bearing
Why does my drive "Growl" when I turn?
Water is leaking into my boat from the transom

Replacing your Trim Sender Switches
My Trim doesn't work but my Trailer Switch does
My Trim Gauge is Pegged

Rebuild your Alpha One Upper Driveshaft Housing Assembly
Rebuild your Alpha One Lower Gear Housing Assembly

Check your Engine Alignment
Check for Excessive Steering Play
Troubleshoot an Overheating Problem
Should I remove my thermostat?
Why do I overheat when going fast?
Troubleshoot a No-Crank Condition
Troubleshoot a No-Start Condition
My Engine Backfires and/or Surges and has Lack of Power
What is an Anti-Syphon Valve?
My Engine blows Steam from the Exhaust
Why do I hear a "clakity" sound while at idle?
Exhaust Manifolds...IMPORTANT Information
How do I Winterize my engine?

What is Galvanic Corrosion?
I have a Bravo III Galvanic Corrosion Problem
What is a Mercathode?
All about Zinc Anodes
How do I check my carburetor?
What carburetor do I have? A Rochester or a Mercarb?
I have water in my fuel
My fuel smells like varnish
My fuel is old
My engine has been sitting for several months without being run.

I have a Mercruiser 470, 485, 488, 190, 3.7L Engine
I have coolant dripping from the front of my engine
Can I install a regular Alternator instead of the Stator-Rotor?

Converting an OMC to a Mercruiser

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