gearbox advice needed

[ka-lin]

It's a shame that my first post here (hello, forum! ) is about a technical problem.....

What actually causes the 4th gear to jumps out while decelerating with engine as a break at 4th gear?

When I put 4th gear in, if i press the gas pedal, everything is fine, until I release the gas pedal, and let the car to kill the speed with engine...Only in this case the 4th gear jumps out..

Things I've checked/tryed:

1. Another input shafts - a little bit better, but still not dramatically improvement. 4th gear jumps off while decelerating at high speed.2. Changed direction of coupling sleeve of 3&4 syncho - even worst:annoyed: 3. Tryed another 4th gear selector (pressing it out with a press from old input shaft and put it into another input shaft) - nothing improved.4. Tryed another synchro (baulk) rings, nothing improved.

The synchroniser hub looks fine, all the clearances are fine, all gears, especially the 4th are fine.

Please note that If I put a little bit harder the 4th gear in, the things got a little bit improvement. But not for long.

I'm ouf of ideas. Please, could anyone to help, and give mi direction what can be that, because every day I remove, disasemble, replase something, assembly and mount the gearbox. I've do that probably 15-16 times, until now..

[480sx]

Your 4th gear shifter fork is broken. The part itself is not expencive, the labor can be if you dont do it yourself.

[ka-lin]

Shifter fork? ?You mean that part that actually moves the coupling sleeve between 3rd and 4nd gear? How can I to determine where is the damage exactly? Thanks, mate

[ka-lin]

Could be overfilling to be the reason?