[keislerNick]

That plug is the pivot for the reverse, overdrive lever which has forks with guide pins in slid into the bottom of it. By taking that out it pulls the clip of the lever. The lever however stays upright and will not fall, problem is you cant get the clip back on without taking the trans apart. Most of the time we have repaired the trans the customer will put the bolt back in and it will push the lever over and break it pinning it against the gears locking the trans up. Bottom line you should never have to remove this unless you are doing repairs to the reverse setup.