Took me a few days to reply, sorry! You guys have a very active forum here, so I had to sift through a page or two of threads!
I'm going to start with your #3 question:
when should you perform your first fluid change?
The short answer is - it depends.
Climate, hours used, and type of usage all affect the fluid condition in the transmission.
If you live in a wet climate, or one that has great fluctuations in temperature, your trans case will draw moisture eventually. It's not a huge concern, but I know a lot of these units I see at work will sit all winter, and run only in the summer. That sitting all winter is what allows moisture to creep in.
Hours used obviously is the major concern. I've seen fluid in transaxles with 500 hours that looked crystal clear, and some at 250 that were sludge. If you have a relatively flat property you mow and you don't tow anything behind the unit, do any plowing, etc - you could easily go 300 hours before changing the fluid. Personally, if it were my unit, I would run it for a minimum of 50 hours before changing the fluid, and a maximum of 150. The kind of heavy use that my tractors see would make me tend towards sooner rather than later.
The first change will have more "break-in" contaminants from the metal-to-metal wear that initially occurs. Most likely, the fluid will only need to be changed once or twice in the life of the tractor - but again, it depends on the type of use it sees.
question #1:
how effective would "several" incomplete changes be -- by using a vacuum pump
If you don't want to remove the trans, you could easily replace a good portion of the fluid by using a vacuum pump, and it done more regularly yes, that method I believe would be effective in replacing the fluid.
question #2:
why is it better to perform this with the rear wheels off the ground?
The reason I believe that they recommend you purge in both the engaged and bypass modes is to properly circulate all the fluid - and since the pump and rear diff share the same fluid, getting the gears and axles to move the fluid they are immersed in as well can help to ensure that all the air is purged into the expansion tank. I don't think it is absolutely crucial, but what the heck - it only takes a second to jack up the tractor. You can purge in bypass mode with the wheels on the ground if you like, that doesn't make a difference in my opinion.
I'm going to start with your #3 question:
when should you perform your first fluid change?
The short answer is - it depends.
Climate, hours used, and type of usage all affect the fluid condition in the transmission.
If you live in a wet climate, or one that has great fluctuations in temperature, your trans case will draw moisture eventually. It's not a huge concern, but I know a lot of these units I see at work will sit all winter, and run only in the summer. That sitting all winter is what allows moisture to creep in.
Hours used obviously is the major concern. I've seen fluid in transaxles with 500 hours that looked crystal clear, and some at 250 that were sludge. If you have a relatively flat property you mow and you don't tow anything behind the unit, do any plowing, etc - you could easily go 300 hours before changing the fluid. Personally, if it were my unit, I would run it for a minimum of 50 hours before changing the fluid, and a maximum of 150. The kind of heavy use that my tractors see would make me tend towards sooner rather than later.
The first change will have more "break-in" contaminants from the metal-to-metal wear that initially occurs. Most likely, the fluid will only need to be changed once or twice in the life of the tractor - but again, it depends on the type of use it sees.
question #1:
how effective would "several" incomplete changes be -- by using a vacuum pump
If you don't want to remove the trans, you could easily replace a good portion of the fluid by using a vacuum pump, and it done more regularly yes, that method I believe would be effective in replacing the fluid.
question #2:
why is it better to perform this with the rear wheels off the ground?
The reason I believe that they recommend you purge in both the engaged and bypass modes is to properly circulate all the fluid - and since the pump and rear diff share the same fluid, getting the gears and axles to move the fluid they are immersed in as well can help to ensure that all the air is purged into the expansion tank. I don't think it is absolutely crucial, but what the heck - it only takes a second to jack up the tractor. You can purge in bypass mode with the wheels on the ground if you like, that doesn't make a difference in my opinion.
