Gearbox issue, forward works fine while reverse doesnt engage, Volvo HS63VE gearbox

[MochiCraft35Fly]

Hello all,

I have searched the forum for threads descrbing similar problem as we are experiencing, but havent found something similar. I apologize in advance I have missed a relevant thread.

The boat in question is ACM 38 Excellence, twin D4-260B with HS63VE , reverse gearbox.

The issue we are expereincing, as described in`title, is that starboard engine or rather gearbox doesnt engage in reverse, while it engages in forward just fine.

Here is what we know for fact:
1. Issue started appearing last year, occasinaly, only when engine/gearbox was warm. Next day, when starting the engine, everzthing would be fine
2. We changed the solenoid valve on the reverse control link, but the problem persisted
3. We ruled out the Control level issue, or PCU issue by reconnecting cables from starboard to port engine PCU
4. We tested voltage on the reverse gear control link to find out it changes once control level engages into reverse
5. We also tested engagement of the control link by leaving spare solenoid` connected to the control link, while outside gearbox housing, to find that it opens as it should.

The conclusion is that the root cause of this issue is the gearbox itself and not electronics of the EVC system.

The mechanic suggests taking apart the gearbox, the control housing to be exact, but would like to better understand how mechanics of the gear engagement work before I go forward with any additinal guess work.

A manual for HS63VE would be highly appreciated as I dont have one.

Thanks in advance.

 

[vas]

had similar issues on engaging fwd on my port engine, different gbox though (mine was twindisk)

Crude explanation (very crude!) assuming a hydraulic box:
there is high pressure ATF oil being pumped about in the box
when you try to engage gear, a diverter valve assembly directs the oil to the right place so that the multidisk assembly "locks" engages and propellers move.
Now, if there's wear in this thing, oil pressure leaks and doesn't arrive at the multidisk assembly to engage shafts and rotate props (doesn't mean you get a leak, oil pressure leaks inside the box, no signs outside!).
This can be on one of the directions and not both. If in both, you may have to search at the pump part but from what I hear it's extremely rare.

Cut a long story short, doubt it's realistic to attack it on the spot, best to get a qualified mechanic to remove it from the boat, open it up and test/repair it.