Is there a 2 1/2 hp flotec sprinkler pumpI got to replace a 21/2 pump but a can not find it anywhere. Maybe somebody put a bigger motor on it and that is why it getting confusion

recheck the seal -gasket and housing [crack or warpage]

https://www.pentair.com/en-us/products/residential/water-supply-disposal/water-supply-pumps/pentair-flotec-fp5172-thermoplastic-sprinkler-pump-1-5-hp.html

Is the pump a 120 or 230v pump? Is it grounded properly?

That will be a difficult locate!
it is stamped on the capacitor itself. Do you no longer have it? Or is the stamp no longer readable?
The 5100 Sprinkler series owners manual is linked below...
if the capacitor/part is not identifiable within that, there is a support phone number you can try? Maybe technician within their service department maybe able to help you personally.
http://www.flotecpump.com/resources/images/527.pdf

good Luck

i believe you have it wired wrong, i dont have enough info here to tell you what you did wrong. look at your instructions again and double check everything. you may have damaged the pump motor. basic wire hook up is black to black and white to white and green to a ground. black is your hot (load)
white is your neutral. thats about all i can tell you from the info you gave

I've never heard of a shift sell for a flotec water pump. That is if you are looking for a part for a Flotec sprinkler pump. Maybe you're looking for a shaft seal.If you need parts or a manual you can look at www.flotecpumps.com The flotec part number for the mechanical seal and gasket kit is:5PP5000. You can search their web site for local suppliers, I'd call first to see if they'd have part in stock. Follow directions when installing. Do not use oil or grease to lube new seal. Liquid dishwashing soap is best.

The impeller screws on the motor shaft. First replace the through bolts in the motor. These are the long bolts, they will just cause headachs. On the back of the motor their will be a place to hold the shaft from turning, If you hold the shaft the impeller just unscrews. If you look in the center of the impeller it may have a set screw holding it to the shaft. If you have one of these it will be a left hand screw. Then you will need to break the impeller free as the brass that holds the impeller on will stick to the stainless steel of the shaft. Don't let how tight this is fool you when you put this back together it just goes on hand tight. Good luck

Try to match it to sta-rite PLBC

green to srcew on the motor. this is ground.,
Black on T1
Red on T2

If the rotation is going the wrong way, simply switch the black to T2
Red to T1.

Check this before you couple it to the pump..

it might be that the pump is prewired at 230 volt and you are running a 115 power supply to it, if motor just humms and little water comes out this might be your fix