[MidwestManiac]

I've ALWAYS seen 2.2 & 2.0 qts referenced for a refill. The larger #'s are for a dry fill. The real problem here is ppl consistently fill the trans fluid wrong, document their incorrect method, then other ppl follow it without ever checking the correct way for themselves. FWIW using the correct method to fill removes any question of amount. The amounts quoted are useful only for considering how many quarts of fluid to buy before starting...they have nothing to do with filling. If you're significantly off from the quoted 2.2/2 qts its also an easy way to identify a larger problem.

Most importantly:
You fill using the fill plug, until it drips out of that plug...with the car flat & level. Put a little vinyl tubing on a funnel, the trans fluid goes down slow due to viscosity/tube size but it really isn't any more work once you're accessing the drain plug from below anyway IME...you should loosen the fill plug first regardless, then just stick the tube in there at the same time. 1 extra time sliding under the car to tighten the fill plug & you're done.

Never in my history of googling "Toyota c60 LSD oil capacity" has 2.0qts popped up. That's more of what I'm getting at

 

[MerryFrankster]

1st to 2nd lockout is a thing on transaxles like ours (1st and 2nd syncros on the output shaft) in high-revving cars. In brief the input shaft just keeps on spinning even with the clutch engaged and delays the syncro engagement. Things you can do about it is replace the 2nd gear syncro to improve its grip and/or use a lightweight clutch disc or a twin-disc clutch with lower moment of inertia. Changing fluid to a lightweight shockproof could also help.

 

[Funnyman]

Is it really possible for excess oil to prevent gear shifting in a manual transmission?? I’ve heard of automatic transmissions being sensitive to oil level since they shift on hydraulic pressures, but a manual transmission only has gears sliding on shafts, and synchro rings made of brass engaging a tapered steel surfaces. I can’t see how excess oil could hurt anything but possibly the rubber shaft seals (due to elevated gear case pressure?)
I have read that some manual transmissions will baulk at high rpm shifts. I know my S51 transmission occasionally doesn’t like to shift at high rpm. But what’s the point of a high revving 2zz engine if you can’t shift gears, at high rpm? I believe there are hundreds of 2zz engines running with C60 transmissions. And I doubt they all shift gears at low rpm’s.

Yes it's possible (Toyota C 6 speed series does not have breather valve). I did have made this mistake. My previous transmission was fine before installing it. But after over-refilling the gearbox, I started to have more difficulties to shift gear. I tought it was because of winter season. The trans has started to make whine sound after 6 months of overfilling and 2nd/3rd synchros have started to failed. When pignons/diffferentials/ect are spining quickly while splashing oil, it create high pressure. And no need to go fast to create high pressure. From the video below, imagine if the transmission was fully oil filled.