It's a 14 hp ... 42" cutting deck
It just quit going ....5th gear....1st gear....it doesn't matter
Do I need to put transmission fluid in it??
Maybe tighten up something?

Thanks

 

Without at least a model and ser. # how would we know?

 

And, "it just quit going"? Like you put on the brakes or did it coast to a stop or did it gradually stop moving over the past, say 2 mowings or 4 mowings? Or was it running fine like it always does then 3 feet later it was not going anywhere?
Did it growl, grind, squeak or squeal? Did it bump or jerk? Did it make a noise? Did it NOT make a noise?
Was you going up hill, level or down hill?

 

Check for a broken belt dude!

 

I agree, the belt most likely came off.