Boat Transmission: Stuck In Gear

 

A shift-interrupt switch system aids in shifting the drive into and out of gear. It  senses a load on the cable housing when the driver shifts gears. Sterndrive Parts illustration.
A shift-interrupt switch system aids in shifting the drive into and out of gear. It senses a load on the cable housing when the driver shifts gears. Sterndrive Parts illustration.

An acquaintance of mine recently bought a new-to-him boat. He was out in it for the first time when he discovered he couldn’t get it out of gear, so he called me to ask what the problem might be. It would make a better story to say I knew what it was right away,  but it took me a while to figure this one out. Then, once I had, I wondered why I hadn’t thought of it sooner.

Clearly, his shift-interrupt switch had stopped working, which is why it was stuck in gear. Nearly all marine engine and drive packages that use “dog clutch” gears also use a shift-interrupt switch. That includes MerCruiser’s Alpha One drives, Yamaha outboards, and old OMC Cobra drives, among others.

The switch momentarily interrupts the ignition power, which allows “dog clutch” gears to mesh easier at lower speed. In the case of shifting out of gear, the load is relaxed on the meshed gears, enabling them to disengage.
The switch momentarily interrupts the ignition power, which allows “dog clutch” gears to mesh easier at lower speed. In the case of shifting out of gear, the load is relaxed on the meshed gears, enabling them to disengage.

A shift-interrupt switch system aids in shifting the drive into and out of gear. It’s mounted in different places depending on the manufacturer, but the interrupter is usually a microswitch attached to a floating mount, which senses a load on the cable housing when the drive is being shifted into and out of gear. The switch momentarily interrupts the ignition power, which allows the gears to mesh easier at lower speed. In the case of shifting out of gear, the load is relaxed on the meshed gears, enabling them to disengage. Listen closely, and you can actually hear the engine cut out for just a millisecond.

If you find yourself in the same boat (pun intended) don’t call a lemon law attorney. Call a mechanic. You’ll be back on the water in no time at all.

Tow Boat Powertrains: Direct-Drive vs. V-Drive

Most boaters start out with the classic runabout as their first boat. It’s great to get the family out on the water together. Then it happens. Your kid goes out with another family and they have a ski boat, an inboard, and it’s waaaay better than your runabout for skiing and wakeboarding.

A direct-drive setup helps center the weight in the boat and makes a smooth, flat wake at higher speeds.
A direct-drive setup helps center the weight in the boat and makes a smooth, flat wake at higher speeds.

Now your kid is whining for a tow boat. Don’t fret. Odds are you’ll like it better than a stern-drive or outboard-powered runabout. Inboard tow boats are fun to drive. They have a better hole shot than anything on the water. They turn more crisply and sharply than nearly any other kind of boat, and they all have that magic thrum of V8 power.

There are two kinds of inboards, a direct-drive and a V-drive, and they’re used for particular disciplines in water sports.

First, a direct-drive features an automotive V8 mounted longitudinally, flywheel at the rear as it would be in a car or truck, but angled downward in the back. Behind the engine is a transmission with a drive shaft that comes out the back and is routed through the hull. It’s the same power path as a rear-drive car.

Direct-drives are the drivetrain of choice for water skiing because they were built to create soft, flat wakes at 30 mph and above. They can be made to work for wakeboard applications, but that usually involves bringing big, heavy water bags onboard, a practice so cumbersome that it’s just easier to buy a different boat. If you’re interested in doing mostly skiing, the direct-drive is what you want.

With a V-drive, the engine can be located farther aft. This makes bigger wakes for wakeboarders, and opens up room in the cockpit.
With a V-drive, the engine can be located farther aft. This makes bigger wakes for wakeboarders, and opens up room in the cockpit.

If your kids are into wakeboarding — and odds are good they are — you want a V-drive. A V-drive also features an automotive V8, but it’s mounted with the flywheel — the rear of the engine — facing forward. The transmission is mounted forward of the engine. The output shaft from the transmission comes out the back, goes under the engine, through the hull, to the propeller. Essentially, the terms direct-drive and V-drive refer to the path of the power. V-drives are better for wakeboarding because the weight of the engine and transmission is farther aft. The stern of the boat rides lower in the water and throws a larger wake.

As with any boat, it helps to know what you’re going to do with it before shopping. It’s especially true for water sports boats.

Boat Transmissions: Shifty Issues

Ski boats, some cruisers, and high-performance boats that don’t have shiftable stern drives use transmissions instead, and that particular piece of the drivetrain is often ignored, which means used boat shoppers should pay special attention to it.

One of the biggest causes of transmission failure is too much throttle in reverse gear. It can happen when trying to keep the bow from hitting a piling, or when you’re trying to power the boat off the trailer at a shallow ramp, or stopping before you run over a downed skier.

This PCM transmission is designed and optimized  for ski and wakeboard boats.
This PCM transmission is designed and optimized for ski and wakeboard boats.

To keep reverse gear from failing, the rules are quite simple. No more than 2,500 rpm in reverse gear. No shifting at more than 1,300 rpm, either. Two other culprits are low fluid levels and moisture intrusion.

While you’re checking the transmission fluid level, take a moment to look closely at the fluid and smell it. It should be a translucent reddish pink, and should just smell like plain old automatic transmission fluid, which doesn’t have much of an odor. If it smells burnt—and if you’ve ever smelled burnt transmission fluid before, your mind is probably recreating it for you right now—caveat emptor.

Visually inspect the fluid to see if it looks murky or emulsified or shows other signs of moisture intrusion. Even trace amounts of water inside a transmission can wreak havoc at the temperatures at which transmissions operate—roughly 130 to 150 degrees Fahrenheit.

Typically, fluid should be changed annually, and good old Ford Type F or FA works best.

Low fluid is a leading cause of clutch failure, so keeping fluid at optimal levels is critical. To check the fluid level, start the engine, shift it a couple of times into forward and reverse, turn it off and check it quickly, within a minute. If the oil cooler is mounted above the transmission, when you turn it off the oil will drain back into the transmission. So if you check it after it’s been sitting too long you get a false fluid reading. It will look as though it’s overfilled, which also is a no-no.

In general, one-speed boat transmissions don’t produce any debris, so there’s no filter to change;  there’s nothing for the filter to catch until something major fails, at which point you need to remove and rebuild it.

If you can get a sea trial, do it, and run the transmission lever through several gear changes to be sure the transmission is functioning properly. And remember, don’t use too much throttle in reverse.