My car wont stay in first gear! ahhhhhhh 8v jh motor 5 speed

[lovinmaracco91]

ok so just recently my car started jumping out of first gear
it will stay in if i keep the rpms very low but not for long and if i go heavy on the throttle it pops right out
i changed the fluid a while back and it wasnt having any problems for like 2 months after it happened
its only first gear
any help would be great

[Broke]

Disconnect the linkage from the trans (pinned rod and ball/cup connection) and then manually select 1st gear. You can select it, then unhook the linkage as well.

Anyway, once the linkage is off, make sure the trans is fully selected in 1st gear.

Hop in, press the clutch, start the engine, and try pulling away.

If it pops out of gear, there is damage inside the trans, or something with the selector.

If it stays in gear just fine, the linkage is pulling it out of gear under load.
It could be a linkage alignment issue, it could be bad engine mounts allowing the engine to move and pull the linkage tight.