MG Car Repair: pops out of gear, shift fork, car transmission

Question
why does my 67 midget pops out of 3rd gear under hard acceleration

Answer
Hi Mike,
Popping out of gear can be caused by several things. First pull up the shift boot and put it in 3rd gear to see if the shift lever is close to contacting the shift tower. If so, drive the car and watch to see if a movement in engine or transmission mounts allows the shift lever to contact the tower. If so you just need to correct the mounts. If not, then it is inside the trans.

Inside the gears have a large spline on the gear itself that is engaged by a sliding hub when you shift. The teeth of this spline over time and ware can get worn at an angle which allows the hub to "walk" out of gear under load. Other factors can be too much end play in the gear or worn shifter forks or even a weak detent spring that holds a detent into a groove to hold the shift fork in place.
All of these need to be very closely examined by an experienced British car transmission mechanic as the angle ware in subtle and hard to see.

Howard