Port Side Engine Reverse gear problem

[doverden]

On my 2005 Open, with twin D6-310 Volvos, I am currently experiencing a problem with reverse gear on the port side transmission, but only after boat has been underway or reached normal operating temperatures for 20 minutes or more.  At this point transmission pressure is normal when in neutral, but as soon as I shift to reverse, pressure drops and also RPMs drop to the point of stalling the engine, and I have no power in reverse on the Port engine. Reverse mode is fine when boat is first started and not yet at temperature.  Thought maybe there was a crab trap line caught in the prop but checked this and can find nothing or anything affecting the port screw and prop. (In my introduction post I mentioned the boat floated off my boat lift during hurricane Mathew..wanted to point out this problem with reverse surfaced before the hurricane so there is no possible cause from that.)
Any suggestions please?

[johnhesch]

Assume you have a ZF63?

How long has it been since fluid/filter change? you'd be surprised how much gunk builds up. Make sure its correct fluid.

Do u have a trolling valve?

Forward is ok? check pressure with actual mechanical gauge too. The VDO sending units can fail.

There is a manual override on the transmission too. You can test the transmission that way to eliminate the electrical portion.

PM me.

John

[doverden]

Assume you have a ZF63?

How long has it been since fluid/filter change?  you'd be surprised how much gunk builds up.  Make sure its correct fluid.

Do u have a trolling valve?

Forward is ok?   check pressure with actual mechanical gauge too.  The VDO sending units can fail.

There is a manual override on the transmission too.  You can test the transmission that way to eliminate the electrical portion.

PM me.

John

---

Thanks John for the response. A Hurst filter kit was installed in October of 2015 and fluid changed then. Not sure what a "trolling valve" is as it relates to my Tiara but there is nothing in any of my documentation that mentions it so I assume not. Forward is just fine and boat reaches full power and smoothly. I will have the other items checked out. Boat is currently hauled and will be put back in the water mid-January at which time the transmission will be tested.

Dennis