True that.

I finally changed the gearbox oil and diff.

I used Amsoil synchronmesh MTF for the box and Amsoil 75w110 for the diff.

The gearbox feels more notchy than my 8 year old mtf... Just had a short 1 km drive, but barely could get the stick in reverse. Even worse than the old honda mtf stuff. This amsoil feels like water.

Is this a normal experience? Outdoor temp was about 15 C. Fresh fluid.

Secondly, I hear more gear whining than before. Not sure where it comes from exactly but I think the front/gearbox. I heard it most clearly when slow accelerating from zero, I think only on power when press the throttle, not when coasting or less audible. Its not overly loud, but it easily reminds of the reverse gear or a straight cut gearbox. Just not as loud.

Anybody can tell me what this is?

Added proper amounts?

Give the tranny fluid some time to mix with the remnants of the old fluid, it can take a couple weeks and you may feel changes. Amsoil is definitely not like water, it is thicker than Honda MTF and much more thicker than 8 year old MTF which likely sheared down to water like consistency after that age.

15c is too cold for amsoil, If it were 25c out it would feel smooth as can be. If you drove your car for like 20-30mins at hwy speed you would notice a drastic improvement because it would heat the up. Either deal with it or switch it out for gm syncomesh.

I've used honda mtf, amsoil, and gm syncromesh all within a short time frame for comparison. Honda is the worst out of the bunch. I use gm syncromesh in the winter and amsoil in the summer. The GM syncromesh works VERY well in the cold, but not as good as amsoil is when it get very hot.

I can't comment on the diff fluid as I've never noticed a difference from one to the next.

Yes sir till it poured out the filler hole. About 0.85L for the diff and 1.6-1.7L for the gearbox.

I can confirm the mtf didnt shear down to water. It was very similar to the Amsoil. Similar like a fresh engine oil viscosity or a bit thicker.

When moving the gear stick, it feels like going through a very low viscosity with little resistancy. And then suddenly for reverse or shifting back to first, it felt like I had to push it through firmly, like something was holding it back to get it in. The honda mtf was getting a bit like that when cold recently, so due to its age, I expected an immediate improvement. Not to get worse when at medium cold temp.

Thanks for your info. I just dont get why it got worse than old honda mtf when cold.
The honda mtf used to feel thick when cold so you had to push with some effort into gears untill it warmed up. Now with this amsoil at cold, it still felt thin and easy to move the stick, but I felt more resistance just before getting it into the gear. Like if you hit things in the gearbox before it goes into gear. Like if you have to push it trough a too narrow space. Not sure how to explain. I could barely push it into reverse when parking. I had to use quite some force and then it kinda snapped in reverse. In all years never had this. So just wondering if that is part of the Amsoil? Or my gearbox works better with honda mtf? I mean even if I take a short ride I need to get it in reverse sometimes without feeling im braking the gears...

The honda mtf was in the car from about 2010-2012 till now. Could it be that it was an older mtf that was thicker when cold? Then amsoil or current honda mtf?

Honda MTF is somewhere around 6.0 cSt @ 100C and Amsoil is 10.1 cSt so it's significantly thicker.
"Measuring" the viscosity by just looking at it or feel it with your fingers is not very accurate and most often your mind is biased and it will fool you.
Drive it until it's properly up to temp and I bet it will feel much better, after that you can decide if you want to go back to a thinner viscosity oil instead.

You do have the car stationary when you try to put it in reverse? Sometimes it can help to double clutch it.

Sounds to me like you might have a problem in your gearbox. I've never heard anyone report this kind of change switching grearbox oil, no matter the brands.