most likely your tensioner spring is worn that holds tension to the belt when engaged , or you may just get a inch or 2 smaller belt.
why does my rider cut off when i engage the blades
look for the engage switch that has a picture of blades
Fix the drive belt.
check to be sure the blades have free movement. usually if you have this problem it is caused from something stopping the blades from rotating therefore it stops the engine
If John Deere mower blades won't engage, it could be due to several issues. Common reasons include a faulty electrical connection, a blown fuse, or a malfunctioning safety switch that prevents the blades from engaging. Additionally, a worn or damaged belt that connects the engine to the blades may be the culprit. Checking these components can help diagnose and resolve the issue.
Lever on right side of steering wheel, push up
The STX-38 should have an electric clutch for the mower deck. The switch to engage it is on the right rear fender. It is a toggle switch. You will have to pull up on the switch and forward to engage the blades.
Most lawn tractors don't have any fancy clutch system, but simply use the belt to engage and disengage the blades. When the blades are disengaged, the drive belt is slack and there isn't enough friction to the pullel to drive the blades. When engaged, the belt is taught and the belt drives the blades. Tension is controlled by a spring loaded pulley. When you pull the lever to disengage the blades, you pull this pulley away from the belt. When you engage the blade, the spring pushed the pulley into the belt, tensioning it.
there already engage
check the front and back belt pulleys and if the elt is on the right side of the engager.
pto switch energizes a vacuum solenoid which puts pressure on the pto belts
If you are saying that the mower shuts off when you engage the blades (or put the lever for the blades in the up position) then the most common problem is a bad seat safety switch. This is located under the seat. It has two wires going to it.