When I shut my doors they both shut fine (2door). The problem is when I'm driving both doors shake and make deep thudding and its pretty annoying. I noticed that the striker is fine on both sides but the latch in the door shakes back and forth when i manually close it with my finger. I'm pretty sure thats it but I'm not shure how to go about fixing it. It's kind of odd how its on both sides. Was this just a common problem for these? Will I have to replace them or is there a way to fix it. Thanks for the help.

 

I assume the slack is in the striker side and the hinge side is good.
Do the strikers have the ring / bushing in place? The 72 has a metal one but some cars (like my old Furd) have plastic ones that break and disappear.
Or might the wrong strikers be installed?
Are the doors flush with the quarters when door is closed?
Shakey doors are NOT normal at all. Make sure the 2-stage latches are closing all the way, too.

Missing or totally compressed or rotted weatherstrip can also cause this noise - it happened in my old Furd.
Normal wear in the latch will always have a little mechanical slop.
Replacing the weatherstrip in my car now keeps enough tension on the door to dampen out any slight movement of it.

 

There's also the two small oval door bumpers that could be missing

 

The strikers are fine. They have the washers and are solid, they don't shake at all, no rust on or around them either. I think the weather stripping may be part of the problem, but like I said the latch, when i manually close it with my finger shakes back and forth. The door sits flush and when i grab onto it and pull and push it shakes slightly and makes the thudding noise. Where is a good source for weather stripping?

 

If the doors close all the way with just a light finger pressure, your weatherstrip is probably far gone.
It looks like OPG carries them for the 76 - it is $62 a set for the doors (fair price). They have a 10% off sale until 4-30 as well.