Hello everyone,

long story short, I had a N/A rb25de neo manual r34 skyline. After swaping rb25det neo i had decided to leave it on stock 280hp power.
I left my stock transmission from N/A rb25de neo which is FS5W71C from what i've researched and it should withstand 400ish hp from what i've also researched.
I was expecting the clutch to start slipping, which did not. but heres what happened:
On third day, i noticed slight crunch when shifting on high rpms. Then the crunch noise got even stronger. And now it always crunches if i shift above 2000 rpm (crunches occur when shifting from 1st to 2nd, from 2nd to 3d and sometimes from 3d to 4th).
It will not crunch if i shift using double clutching (with that im able to drive around and shift whenever i want without problems, thou it will still crunch if i shift on redline)
No crunch when changing gears if not moving.
It will sometimes crunch when pulling out of gear to neutral (mostly from 1st).
Will sometimes crunch after engaging gear and i release clutch pedal (the crunch occurs just at the last moment when i lift off the foot from pedal and it disappears immediately).

Thought it was because of the clutch, but changing flywheel, pressure plate and clutch disk did not help.

Any ideas what it may be?
I would appreciate any advice.

thanks

Sychros are like baby clutches for each gear inside the tranny. Sounds like you need a rebuild kit (bearings, seals and synchros) and some downtime. Maybe someone else can verify. The details have me thinking about the transmission input shaft actually being the source of this issue... which is also fixed with a rebuild.

Keep us posted please.