Lost reverse: overheated or shattered reverse clutches

AS7-71CR 1017-008 1.91:1

What Chris sees on the bench

• Shattered reverse plates that took out all the reverse springs, including the pressure plate separator plate, which often warps too.
• Strawberry milkshake in the sump, a thick goo that makes the pump work harder and the transmission overheat.
• A clutch hub on the input shaft with grooves in it, gone black from overheating.
• On one 71 1.91:1, a previous rebuild had put a Speedi-Sleeve on the input shaft when the shaft should have been replaced, and reused a worn bronze washer.
• A reverse plate starting to wear next to a brand new one: the notches and teeth get skinnier and narrower.

What causes it

Ski boats are the classic setup for this failure. A hard port turn can tilt the transmission enough that reverse briefly sucks air, and slamming into reverse right after that is what shatters the reverse clutches. Velvet Drive's installation manual makes a similar point about angle and oil level: max installed angle is 15 degrees at rest and 20 degrees bow-high running, and a steeper angle combined with low oil lets the pump cavitate in rough water. Wear plays into it too. As a reverse plate's notches and teeth wear down, eventually you'll shift into reverse one hard time too many, the cavities that hold the reverse springs blow apart, and the springs go everywhere and get into the pump.

A slipping reverse clutch usually squeals first. If the engine is turning faster than it should for the load, that's often a slipping clutch, and running it that way overheats and warps the plates, sometimes welding them together, and then the transmission can tie up when the other clutch applies. Velvet Drive's own manual is blunt about it: don't keep running a transmission that's slipping.

Fix and prevention

When the reverse plates shatter, you have to replace all the springs, including the pressure plate separator plate. A lot of times that separator plate warps too. Velvet Drive uses 11 of these reverse pressure-plate springs, part number 71-97, common to both the 71C and 72C, and the rule is to replace the full set rather than mixing old and new.

To keep from getting here, take your time shifting. Chris's rule is five seconds from forward to neutral to reverse, instead of banging it into hard reverse. See the five-second shifting rule.

Other things that can look like lost reverse

When to call

If reverse is gone, call (804) 333-3677, Monday through Friday 9 to 3 Eastern, or email sales@halemarine.com.

Related reading: the five-second shifting rule and Velvet Drive torque specs.