Ok let me start with a little back history on the car.
Transmission was rebuilt about 8000 miles ago. Shifts perfectly, never felt a transmission so smooth.
Recently, (past week or 2) when accelerating in first, I get a loud vibration noise that sounds like me engine hitting the firewall, more so when the AC is on.
Today I reversed quickly in a parking lot and the car went about 2 car lengths in reverse, the tires locked up, car bogged and it started moving slowly forward. I pressed in the clutch and the car wouldn't go fully into any gear. I tried holding it in the reverse position and slowly letting off the clutch but the car tried moving forward again. Shut the car off and with the car off it still would not go into any gear fully. (felt like when your reverse gear doesn't line up and you need to roll some, but in every gear.) Started the car, held the stick into second, (because it felt like it was the most engaged) let out the clutch slowly. The car made almost the exact same vibration noise it had been making the past few week just louder. Then the stick slipped all the way into gear and the car started working as normal. Shifts perfectly again in all gears and no sign of any problems.

I first thought motor/trans/torque mounts, but they are all in almost perfect condition. I'm totally stumped on what could cause this.... Maybe I did something wrong on the transmission rebuild, but I have no idea what could possibly even do this...

Please help me oh great Honda wizards!

 

If you put the car in reverse and the car moves forward, and this isn't the result of gravity, it's safe to assume you have internal transmission issues.

 

I would think the same, but how could it "go back" into place and work? The main and counter shaft are locked in by the bearings, and a slipped shift fork would be highly unlikely to go back into place, IMO. What internally would you expect it to be?

 

Provided the shifter is staying in the reverse position when its going forward something has to be bent/broke internally.

 

i was leaning towards the internals as well, I just can't imagine what it could be.. I was thinking maybe linkage or something with the input shaft length. It's a 97 Del Sol transmission with a 96 Civic clutch, pressure plate and flywheel. I had some issues with the starter lining up right and had to shim it to make it work. Didn't know if this was somehow related...

 

Interlock guide bolt. There's a piece that this bolt keeps aligned so that only one shift fork can operate at a time (located at the bottom of all three shift forks, sorry I don't know the technical names off the top of my head). 5th and reverse share the same fork so to speak. Anyways that's where I'd start. The damage will be apparent if this is in fact the source of the problem.