I just finished installing my UPR short shifter into my T5 and now it seems like I can't get my T5 into reverse? Even with the "shift stops" fully backed out it won't go into reverse. It's a used tranny that I bought and with the stock shifter I'm fairly sure It went into reverse before. But now it seems like I'm locked out. I can go into all the other gears fine, but can't budge reverse even with my buddy spinning the input shaft. The transmission is sitting on my milk crate so It won't be installed any time soon.

What can cause this lockout issue?

 

I would try to put the stock shifter back on if you have it and see if it is the UPR shifter, because if its not that then there must be a problem with the reverse gear on the tranny.

 

I can't think of any reason why one shifter would cause a problem vs the next one.
They are basically just a lever rotating on a ball. Without the transmission connected to it they will basically overshoot any gear they are pointed to.

I'm wondering if it's just a case of not enough effort put towards pushing it into gear. You said this thing is sitting on a milk crate?

These transmission need quite a bit more effort going into reverse, even if the gears are perfectly lined up, compared to one of the forward gears. The short shifter may just be taking a bit more mechanical advantage away from you making it seem like the shifter.

 

try putting it in first, rotate the input shaft a little, then go into reverse. that would be the equivalent to putting it in first while its in a car, letting the clutch out a hair so the car starts moving, then clutch and go reverse. probably 50% of the time thats how i have to do it in my car cuz i dont always drive in first when im about to park.