Case 580b Drive and reverse engaged at the same time

My 580b developed this problem after a house demo job. Reverse will engage after a few seconds in drive. I can move forward about ten feet then the machine stops. Pushing the clutch or pressure dump pedal does not stop the reverse movement. I can kill the engine for a few minutes, restart then move forward another 10 feet and the cycle repeats. Reverse is great. Pressures on the gauge seem normal. Its like a battle between drive and reverse with reverse eventually winning. I found other similar posts with no resolution. Thanks!!

A somewhat educated guess would be that the sealing rings on the front of the power shuttle unit are allowing pressure from the forward clutch circuit to transfer and apply the reverse clutch pack. I have seen the sealing rings actually damage the casting where they run and require a replacement casting or have a sleeve installed to repair the damage. There are gaskets under the control valve and adapter plate that maybe could have blown but that is somewhat unheard of, the spool valve cannot pressurize both r and f at the same time

that make senses except why does depressing the clutch/ dump valve not kill the pressure to the reverse clutch. Is there somewhere you know of that line/pump pressure could get into reverse? It could be the reverse clutch seizing without pressure but it relaxed after the motor shuts off for a few seconds. Shouldn't the clutch pedal kill the pressure everywhere in the clutches? Sorry for so many question! Just trying to get my mind wrapped around whats going on inside this thing! Thanks for your reply and info

Further to what @melben has said - If the sealing rings are damaged & the machine has been used for a long time like this, it is possible that the reverse clutch pack has been damaged due to having pressure while forward has been used.
It's possible that it may now have broken a friction disc & the pieces are interlocking causing reverse to be mechanically engaged - without any pressure - causing reverse drive while in neutral.

Thanks Airman! Could be. It just seems hydraulic because it cures itself after the machine shuts off. I believe Im going to have to stop talking and swing some wrenches to fix it. I've got it listed for sale too. See what happens. Thank again!

Sometimes when you shut the machine down, the clutch pack relaxes & the broken plates separate, allowing semi normal operation.
Then when drive is attempted, they interlock again & lock up the pack.

Thanks Airman! That makes perfect sense!