Hello Bob,
"Again I am sorry about all the stupid questions but you can't learn anything if you don't ask questions."
A wise teacher once told me that, with a few exceptions, "The only stupid question is the one you don't ask."
"1) Does this trans need to be clutched between every shift?"
Yes. A better answer is that if you are shifting "on the go," the transaxle needs to be "unloaded." In other words, moving the shift keys between gears with the engine still applying a load to the transaxle will result in rapid damage to the tips of the shift keys and the mating notches of the shift gears.
"2) I am looking for a maximum ground speed of 22 mph; rear tires are 18" diameter."
I doubt you will be able to get close to 22 mph with the MST transaxle. You would need to turn the input shaft 6000-7500 rpm to achieve 22 mph with 18" tires. Maximum recommended tire diameter for the MST is 20". An 820 transaxle with a Gearset Upgrade on the final-drive gears would allow the speed you are wanting.
"3) How much can I exceed the rated 2000 rpm input-shaft speed?"
I wouldn't recommend more than 3000 rpm unless you plan on replacing your input-shaft bearings regularly.
"4) I will have a vertical jackshaft in the build...hoping to set input-shaft speed to drive at approx 2500 rpm while only
turning the motor around 1500/1600 rpm. Is this possible?"
Possible, but not recommended. Your 14.5 B&S OHV single is air-cooled, and the slower you run it, the less cooling air you have flowing over the cylinder fins. You will overheat your engine quickly running it below 3000 rpm. Best to run it at the maximum governed speed -- 3400-3600 rpm.
"I will also be adding a go-kart disc brake on either side of the transaxle or is the internal brake of the transaxle good
enough as a service brake or is it more of a parking (brake)?"
Go with the go-kart disc brakes. There is no internal brake on the MST transaxles, and the external brake is, as Peerless Gear states, a "parking brake," even though most mower OEMs use it as the vehicle brake.
"If I have to or want to change out the clay-type lube for a premium 90 weight synthetic, I would also like to add a drain
plug with a magnet."
MST transaxles already use a petroleum-base 80W-90 gear oil, not the clay-based Bentonite grease. Adding a drain plug would be possible, but with the design of the MST bottom case, one drain plug will not drain all the oil -- you would need four drain plugs, one at the bottom of each section. And as thin as the case is, you would need to weld on thicker reinforcements where you wanted plugs.
Hope this helps.
Respectfully,
Rodney Rom
Rom's Reworks
Butler, MO
