hard downshifting from 5th > 4th

[J__]

my 5th gear went in my old tranny so my mechanic put in a new one for me. same 5 speed but the gear ratio seems ALOT longer than my old one, especially 5th... the tranny he said was rebuilt by him 7 years ago and never been used, he also put in an used buy almost new clutch for me since mine was like a trombone and roughened my flywheel. anyway, 2 problems i found after the swap

 

1. there's a a mild rattling noise when i am in neutral with the foot off the clutch. almost a very very mild grinding noise. and it happens too when i put the car into gear at standstill. the noise is gone under normal driving conditions.

 

2. when im goin at a good speed/rpm and downshift from 5th > 4th, its hard and makes a "clunk" when i put it into 4th gear and i can feel it in the stick. almost like trying to force it into 1st gear from 2nd at 30mph. this happends everytime when i go approx 120km/h at over 3000rpm in 5th into 4th.

 

i rev match, double clutch. and nothing helps still clunkeds into 4th at over a certain speed..

 

is it a syncro? if it was, wouldnt this not happen if i double clutch?

 

i read up on some other tranny threads with hard shifting and some ppl recommend throwing in some redline fluid in there to slip things up a bit. what fluids do u guys recommend? thank you!