I decided to change the transmission fluid in the Hurth transmission of an Universal M18 on a Catalina 27 since I have about 200 hours on the engine since acquiring and not known when it was replaced last by previous owner. The manual says the M18’s used the HBW-50 transmission which takes 0.29 quarts or 300 mL. I removed 350 mL of transmission fluid by suction pump since the drain plug is pretty much unreachable. I scoped the inside of the gear box after the fluid was removed which looked pretty empty except for some slight residual. I put 300 mL according to the manual. I put the dipstick back in to check (not screwing it down just resting it). The dipstick is really hard to read and laying in on a paper towel or white cardboard tends to soak up across the dipstick beyond the full mark. I can see fluid in the quarter inch full notch mark and some droplet formation from the ATF viscosity about halfway below the full mark. Laying it down on white plastic it looks there may be some very slight fluid above the full mark, but I find it hard to believe I would have overfilled putting 50 mL less than what I took out and being able to see the bottom of the inside of the case.
How critical is it to have it exactly to the full mark or if I’m a little above is that a huge deal?
Is there any downside if it is slightly less than at the full mark?
How critical is it to have it exactly to the full mark or if I’m a little above is that a huge deal?
Is there any downside if it is slightly less than at the full mark?
