[Tkey]

2004 3200 Volvo D6 310's.

The port engine is intermittent shifting into reverse. In fact, mostly not at this point. Problem came up suddenly (at a bad time). It will  take throttle commands into reverse but just revvs. All other functions fine on both engines. Thoughts?

[Sans Peur]

The shifting is done by 2 solenoids on the transmission. It could either be the reverse solenoid is going bad (most likely) or not receiving power from the shifter on the dash.
Go below and put a meter on the solenoid wire and have someone shift the lever into reverse. If it is getting power it is the solenoid. You can also swap the connectors between the forward and reverse solenoids. If it still won't go into reverse (when you shift the lever into forward because you reversed the wires) then it is the solenoid. If it goes into reverse and not forward. Then it is the lever.

[Tkey]

I appreciate the reply. I'd thought the solenoid and had a mechanic take a look. They came back reporting slightly low hydraulic pressure and wanting to replace the entire transmission. Crazy. Now that I'm free from work I'll be taking a look myself.

[Sans Peur]

Do you have pressure gauges for the trannies on the dash? If so put it in gear and look to see what it is.

[Tkey]

Just an update, the problem fixed itself and has been reliably shifting for many hours of operation not long after my last reply here. Not my favorite not knowing but I'm guessing electrical.

[Tkey]

I was right. Electrical. Problem re-emerged and I simply cleaned the terminals on the solenoid, which had become a bit crusty.

[Reel Pursuit]

2004 3200 Volvo D6 310's.

The port engine is intermittent shifting into reverse. In fact, mostly not at this point. Problem came up suddenly (at a bad time). It will  take throttle commands into reverse but just revvs. All other functions fine on both engines. Thoughts?

Had similar issues with failed FWD solenoid(theres 2 a fwd and reverse)  you can unscrew cap of solenoid and push bottom to shift manually.
The solenoid should give about 10 ohms if tested with meter.

[Sans Peur]

Yep, that's the thing about electrical, or most any, problems. They will sometimes go away but they will usually return again.

[Tkey]

Yep, that's the thing about electrical, or most any, problems. They will sometimes go away but they will usually return again.

It returned. Ended up replacing the whole transmission. Was the same price as replacing parts.