Hodge, I wasn't referring to the implement pushing the tractor. I know that's what the OC is primarily intended to fix. There is always some back feed with over running clutches, it's why the peddles on a bicycle move if you don't have you feet on them while coasting. Looking at the design I think enough power will be back fed to keep the main shaft turning even with the clutch in and the transmission in neutral. I'm just curious if the level of force being transmitted at full PTO speed is enough to upset shifting. You'd notice it as a more audible clack or even slight grinding while changing directions while mowing compared to doing it with the PTO disengaged.
Eric, I was just talking about changing directions, should have mentioned that in the first post, but it is possible to shift gears on the fly but not recommended as you say. Up shifting is fairly easy as long as you don't miss your shift. I used to do it all the time from 2nd to 3rd while mowing with out old Wheel Horse.
It's very similar to shifting an unsynchronized semi tractor transmission if you know how that's done. When up shifting you put the clutch in, guess how long to wait for the gear you want on the main shaft to slow down to match speeds with it's partner on the counter shaft (it's similar with a constant mesh design), slap the shifter quickly into gear and let the clutch out. If you did it right it goes into gear quietly, a little off and you can hear an audible clack, too far off and it grinds. If you miss you've got to come to a stop or double clutch and spin the main shaft back up.
Down shifting is similar in principle, you've got to match the gear speeds, the difference is you must speed up the main shaft instead of letting friction slow it down. You put the shifter in neutral and let the clutch back and rev the motor up til the set of gears you want are matched and then put the clutch in and slap into gear. The trick of course is knowing what speed the gear you want is turning which is different for every machine and difficult under the best of circumstances. In semi tractors once you get the hang of it you can do both shifts without using the clutch but doing it that way is even less forgiving of mistakes. The primary difference in a tractor is you're working with a set of gear ratios that were not designed to do it and you have less momentum to work with as well as higher rolling friction (makes you slow down faster) to deal with. You can also run out of your RPM range very quickly and you don't have very fine control of the engine RPM with the foot throttle. It's not bad on the flat and low speeds but add hills and road speeds into the equation and it gets ugly fast.
In the Ford 4500 I've talked about my dad and I used to drive it back and forth from his friend (the owner's) house to ours which is about 2 miles of hilly back roads with a nasty left turn at a stop light on top of a hill. When driving on the road we would start it in 3rd HI on the flat, 2nd HI on hills and shift to 4th once it got up to speed. Going up steep hills we would have to double clutch and rev match back to 3rd at the bottom to climb the hill. 4rd is so much taller than 3th from full speed in 4th you actually have to wait for the tractor to slow down while holding it at max RPM in neutral before you can put the clutch in and shift into gear. This worked fairly well as long as you didn't try to shift going up hill. The first time we did that my dad made that mistake on the hill with the light and missed his shift. He stalled it (that hill is very steep and 3rd can only do it near maximum rpm) and when he started again the fronts tires came off the ground very briefly because of the angle and the weight of the backhoe. We both turned white (I was following behind in the truck).
It's a very touchy affair under the best of circumstances. I consider myself very good with manual transmissions, as good as my dad was, better by far than any of my friends and driving that thing on public roads is still the most difficult thing I've ever done driving. Around the yard it's not nearly as bad but it takes a while to learn and everytime you mess up you damage the transmission a little.
