Garage plates water damage; need refresher course on plate raising with threaded rod & concrete.
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Or you can try this. See illustration click for full size.
The over all length is 2 or 3 inches longer then your garage door or some suitable jacking place. You put it in position with eh hinge section bent slightly and then a small push will allow you to life considerable weight a couple of inches.
The stop will prevent it going past vertical and you can put a clamp round the moving part and the stop to hold the position.
NOTE for safety you should shore up the lifted part with other timber or screw type support jacks before you start work under the garage.
Always work as if the worst is going to happen, one day it will and you will be grateful you were prepared.
A lever may be easier.