Teague’s Take: It’s Drive Time

This issue’s Q&A session features a few drive-related questions

As Seen In Speed On The Water

As Seen In Speed On The Water

Two issues back, I answered a few questions regarding propellers. This time around we have a couple of drive-related inquiries. I won’t be doing this every issue, but if you have a question for me, please ask. I like tech questions and think Q&A formats can be informative and fun.

LAZY SHIFT

Q: I have a 2005 32-foot Advantage Victory with twin MerCruiser 496 Mag HO engines and Bravo One X drives. The starboard drive is very slow to fully respond to the shifter at the helm. When shifting into gear in reverse and forward, the prop begins to spin immediately, however, it spins with very little power.

It takes 5 to 10 seconds and then the clutch locks up and the boat responds appropriately. The port drive responds immediately as did the starboard drive prior to having it serviced. I recently had the drives serviced, which included removing them, checking the alignment and replacing the drive oil.

The problem with the starboard drive started shortly after servicing with a brief delay that has grown to 5 to 10 seconds. I had this same problem with the port drive a year ago, but was unable, at the time, to link it to drive service due to some other factors, although the drives were serviced within the time frame of the problem. The shop ultimately replaced the cone clutch assembly in the port drive unit.

Is it possible that there is air in the starboard drive unit that has accumulated creating an air pocket that is preventing full engagement rather than a problem with the
cone clutch assembly?

Do you have any other suggestions as to the cause of the problem, diagnosis and
the fix for it before I replace another cone clutch assembly?

A: There is no way that it’s related to air in the drive. A Bravo drive is a wet-sump drive and is filled to the midpoint of the upper input shaft. When the engine is running, the upper pinion gear and the driven gears are always in motion. When the cone clutch is engaged, one of the driven gears is locked to the upper shaft, which is coupled to the lower vertical shaft. When the lower driven gear is engaged, the propeller spins clockwise, and when the
upper driven gear is engaged, the propeller spins counterclockwise.

There are brass rings attached to the two driven gears. When the drive is assembled, the driven (forward and reverse) gears must be timed in order for the cone clutch to shift properly. The brass rings are high on one side and low on the other so there is a “wobble” when they rotate. The shifting fork that rides in a slot in the cone clutch goes between the two brass rings on the gears. The shifting fork also has some cam ramps on it that contact the brass rings. When the drive is shifted, the uneven motion of the rings helps to kick the cone clutch into an engaged position.

I don’t believe your problem is from having the drives serviced unless they put the wrong oil in the drives. I believe that the brass rings on the gears may be worn or there is a problem with the shifting fork or cams. There’s a possibility that the problem is only being caused by the shifting fork or the linkage that connects to the intermediate shift cable. There is a setscrew on the shift shaft that also might have come loose. Remove the back cover from the drive to inspect the linkage, shift fork and the setscrew.

It’s possible that the intermediate shift cable wasn’t properly engaged in the shift linkage when the drive was reinstalled on the boat. It is sometimes tricky to get the linkage to latch on the cable end. To inspect that connection, the drive will have to be removed. The linkage is connected to the drive’s starboard side. It must be unlatched to remove the drive fully.

If all of the shifting mechanism is in good order, it is likely that you will need to replace the cone clutch and shifting fork. If the brass rings on the driven gears are excessively worn, replacement of the upper gear set also will be necessary. If there is any metal on your upper plug magnet, it’s possible that the thrust bearing is failing. The debris that is generated can cause the cone clutch to act weird.

BRAVO ONE TO XR

Q: I recently upgraded from a Bravo One drive to a Bravo One XR drive. The new drive
sheared teeth in the upper unit after only three hours of use. In contacting the selling company, they informed me that since I had “upgraded” and not simply replaced my old
drive, I should have purchased a kit, which includes spacers to be installed on the cylinders so the drive cannot be raised as high as the Bravo One. Also, the kit has some kind of part that would be placed in the gimbal housing. Have you heard of this?

A: The first design of the Bravo One XR drive used a more massive universal joint and yoke assembly in comparison to the stock Bravo One. Because of the larger U-joints, it is desirable to not run them at too much of an angle. That is the purpose of the trim-ram
blocks. Also, if your transom is an earlier model Bravo One, the gimbal bearing has to
be changed to the later design that has less of the inner race protruding on the drive side
of the bearing. The Spicer version of the XR universal joint assembly is slightly longer. The
design of the later gimbal bearing provides the additional room needed. The late-model XR
gimbal bearing is easily identified by a red dot on the aft face of the bearing unit.

The aluminum bellows retaining ring also needs to be changed to the later design that is slightly narrower in order to provide adequate clearance for the larger universal joints.

All that being said, it is very doubtful that the cause of your upper gear failure was because you didn’t have the “kit” installed in your boat. There has been a run of teeth breaking off the “forward” and pinion XR gears lately. If your engine is in the 500-hp range or less, was full of oil, and you didn’t hit anything, I think the seller should stand behind it if they are a marine business.

–Technical editor and offshore racing world champion Bob Teague is the owner of Teague Custom Marine in Valencia, Calif.

This article appears in:
Speed on the Water, Issue 15; September/October 2015