If you trim your outdrive up and you loose the ability to shift it typically means the short shift cable is bad and needs to be replaced. Too much slop in cable, it has stretched or worn out the inside isulation.
Here is the adjustment proceedure for the short shift cabel. (this is for a new installation but can be used to make sure yours is set correctly.
One key issue in the proceedure is the distance between the trunion/barrel and the cable end mounting hole distance.
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Trim out drive up 2 inches from all the way down.
Take keys out of ignition!!!!!!!!!!!
Have a second person stand at the prop.
You, remove the short shift cable from the shift bracket.
After the cable has been removed, push the plastic cable end all the way in and hold in place while prop is being spun C’Clockwise..
Have second person rotate prop counter clock wise until the prop is fully engaged and wont turn anymore. Maintain light effort on shift cable plastic end pushing it to keep forward engaged.
Measure the distance from the center of the brass trunion to the center of the round mounting hole in the plastic end. Adjust trunion/barrel to make that distance 6 inches. no more no less! In cases where the shift cable is old but still works well you can adjust this dimension to 5 15/16”. NO MORE.
Put shift control handle in forward FULL throttle position.
Remove the control shift cable from shift bracket at this time.
Install short shift cable back onto bracket at this time.
Take the shift control cable and adjust the trunion so it fits perfectly back into the shift bracket.
Before installing it turn the brass trunion 4 complete turns away from the plastic end and reinstall into shift bracket.
Now put shift control handle in the neutral position.
Have second person spin prop, it should spin freely.
Put shift control into the forward detent position at ~ 10:00 position. NO FUTHER.
Have the second person rotate the prop counter clockwise. You should have solid engagement with no ability to continue to turn the prop.
Now shift back into neutral. Prop should spin freely with no clacking or clunking.
Now shift to reverse to the 2:00 o’clock position detent NO FURTHER!!
Have the second person spin the prop clockwise.
If you have positive engagement with no clunking or jumping out of engagement, you are done.
If it does not fully engage into reverse than look at the shift bracket where the short shift cable mounts and there is a slot. Loosen the 7/16 hex that is touching the bracket and move the stud so you are pulling the short cable.
Try this and retest in water under load.
Anyway there are tests that would tell you if the cable is bad but to difficult to type out here but in general if you remove the shift control cable from the shift bracket, shift the control handle to full forward/wide open throttle and make a mark on the cable end, now go full reverse and repeat. Measure distance between marks, (2 7/8" to 3 1/8") any more and replace the control cable.
Short cable measurement test, remove short cable from shift bracket, push all the way in and spin prop by hand until full forward is made. Make a mark on shift cable end where the plastic stops over the metal.
Now with someone holding the prop from spinning pull the cable end out with two fingers, as soon as resistance is felt mark the inner cable where the plastic cable end ends. Now measure between the marks,
The measurement should beif I remember correctly 1/2 " to 9/16". anymore and the cable or linkage is bad.
