I recently bought a house built in the 50's. It looks in several places that maybe the floor begin to buckle. It also appears that they took a saw and cut between the boards and nailed the floor back down. They did a terrible job of filling the gaps back up and i have places that any wood filler they put in it is gone and you can see the sub floor. Any suggestions?
Sounds like they tried to correct a problem caused by moisture from below by hacking up the floor. Unfortunately, that means that you are past the point of being able to make simple repairs that look good.
First step is to determine if you are getting moisture under the floor - check your crawl space or basement. If a crawl, then it needs a 4 mil vapor barrier over all the dirt. If a basement, you may need a dehumidifier if it's damp down there.
As to fixing the floor, you are looking at using more filler to fill the gaps. Only other way is to remove flooring and replace with new.
There was a lot of moisture but we have a new barrier put down now. One of the first things that we did.
You need to be spending your time and money preventing the moisture in the first place before any flooring goes in.
Moistures going to cause mold and fungus, attract termites and powder post beetles.
Working gutters, grade slopping away from the foundation, no mulch piled up against the foundation.
No flower beds forming ponding of water.
May even need a French drain.
Sounds like you have fixed the problem but not the 'cure'. Had the former owners gone the vapor barrier route first it's likely that the floor would have settled down on it's own.
The bad news is that like I said above, the 'repair' damage is now done and there's not much you can do short of replacing the flooring that will make it look like it should.
I thought complete home renovation is the only solution to your problem.