I did a swap 97 LS motor to 97 Civic coupe. All the wiring are done, no check engine. During a test run, the car moves reverse or forward on gear. Then later on the car suddenly won't move in gear reverse or forward. You can change gear 1st to 5th without using a clutch (no grinding) but you have to use the clutch to put it in reverse. Turn off the car put it in gear without anyone pressing the clutch and push the car, it moves (like pushing it in neutral). It shouldn't because the gear should lock. What could be the problem?

 

check for which axle is not engaged in the tranny.