My test and repair procedure for the Linear Drive (LD):
Disconnect the LD drive rod from the rudder
quadrant so the LD drive rod is easy to move. I strongly recommend removing the entire LD from it’s mount and from the rudder
quadrant and testing it in your shop or on deck
. IF you remove the LD to work on it on deck
then you need to have a small battery
or 12V power source to energize the clutch and the drive motor (they are separate circuits). Or, connect new + and GND leads from the course computer to wherever you are working. They can be 14 gauge or lighter since the clutch uses little current
In my boat, I do not have easy access to the Linear Drive and it is much easier to remove it and work on it in my shop.
When I refer to Voltage it should be more than 12V and in my system was always slightly less than battery
voltage. Engage AUTO to cause the Course Computer (CC) to output V for the LD clutch which uses a circuit separate from the LD drive motor. The clutch circuit should always have 12V on it when in Auto mode.
Measure the Voltage at the +12V output (marked Clutch) on the (CC). If there is no voltage then the CC is not generating the power to engage the LD clutch. There is little hope of repairing the course computer!
Disconnect the power wires from the course computer to the Linear Drive (LD) AT the LD. The easiest way to do that is open up the LD and use thin multimeter probes on the wires.
If you have voltage at the CC but do not have voltage at the LD then you know the wire from the CC to the LD is bad (it could be either the + wire or ground wire). Be sure to use the ground wire for the clutch voltage as your ground point for the measurement. If it is a bad ground wire and you use some other ground you will measure OK but still not have a good 12V circuit for the clutch.
If you have voltage on the CC 12V “Clutch” wire at the LD then you suspect the clutch itself is bad. With the clutch wire activated (Auto at course computer) you should be able to move the LD drive rod in or out by hand and hear the gears in the LD drive motor turning. If you move the rod but do not see or hear the drive motor gears turn then the clutch is bad.
You can take the clutch/drive motor apart fairly easily and inspect the clutch parts
. My clutch did not fail and looked brand new when I inspected it after 18-years and 4,000 hours of usage.
If the clutch looks good then you will need to check the Linear Drive planetary gear
system to see if the SUN gear
is stripped. My old “plastic” sun gear stripped due to operator error after 6-years and 500 hours usage. I replaced it with the “new” bronze gear that will never strip. That bronze gear was used in all LD units after about 1999.
The SUN gear replacement is easy if you are mechanically inclined and have rebuilt car or motorcycle transmissions. Otherwise, find a good mechanic
The entire Linear Drive system is fairly simple and I learned all about it by tearing it apart and playing with it. The first time I explored the LD innards - we were anchored off of Cabo San Lucas in the worse 5-foot rolling swell I had ever experienced. Lying on my back between the battery box
and rudder post while removing the LD from it’s mount and rudder quadrant was no fun.