So, I bought my first shrinking disc and have been using it with very good results. But, I just learned the hard way, that an over-shrunk spot without open access behind it can be a problem. I have enough space behind the panel to hold dolly, but not enough to hammer. Will hammering on-dolly from the front raise this area? What's the proper way to fix this?
How long is a piece of string? Without seeing panel it's damn hard. Can you get a body spoon in the cavity and attempt to put pressure on the low area and use a slapper to stretch and raise the metal?
Yes, in theory. Make sure you are holding the dolly inside firmly and using pressure toward the direction the panel needs to stretch. Even if you are hammering from the outside and the panels needs to stretch outward. Sneak up on it, it won't take much.
This view looking down from top shows the sunk in area. Needs to come out about 1/4" or less. There was a small oil can here and I'm thinking that being at the end of that body crease may have contributed to it sinking in as it did. Again problem is no access to swing a hammer behind it, only room to get a dolly in. Going to see what further advice you guys have before I start working on it. This is the hard part of being self taught.
That is a fairly large area to fix with access mainly from the front. I would cut a section out of the inner reinforcement to allow hammer swing or a pushing tool. It's easy to weld the piece back in. Make it easy on yourself.