1989 toyota pickup r150f pops out of first gear

[Kauai_hawaii808]

Aloha guys, new to the forum,  just wondering on ur guys input on this problem I have.  I have a 1989 toyota pick up 4x4 with a r150f transmission with. 3.0 liter engine,   Transmission pops out of 1st gear when I pulling out from a stop.  I have replaced shifter bushings, and also replaced all synchronizers and bearings in transmission assembly.   Transmission mount and engine motor mounts are still good, no cracks or damage.  Can't seem to figure it out aloha

[Goldrush]

Is it possibly your interior shifter boots? There have been instances to when the boot actually forces the shift handle to pop out of gear. And you said you replaced the bushings. Did you replace them with our HD Shift Lever Ball Seat and socket?

[Kauai_hawaii808]

I test drove the vehicle with the interior shift boots off to see if the body was forcing the shifter to pop,  but it was ok. I replaced the bushings with OEM shift bushings. 

[Kauai_hawaii808]

Also I installed a intermediate helper spring, to apply more spring pressure on ball bearing that locks 1st gear in place. But it still pops out.  Kinda stuck on what's left to repair

[Yotaleigheehoo]

I have the same problem in my stock 94 3.0 v6 5spd. On flat ground, first gear stays put most of the time. On an incline, it's guaranteed that I have to hold the shift lever in place or it will pop out. I've replaced both shifter bushings with Marlin's without success. Anyone know where the problem is?

[Dingman.]

my 4runner transmission use to do that.  i just got used to always holding the trans in first gear when i was taking off.
I swapped the shifter bushings but it would still do it.

haven't had a problem since i swapped transmissions out when i went dual cases.

[Kauai_hawaii808]

If I hold it in I doesn't pop out, if driving casually,  but if I hold it full throttle,  it will pop even if my hand on the shifter.  Can't seem to figure this out.  Torn down the trans 5 times and no luck, any input would be helpful