Hello, the short side of the front axle (drivers side) has some in and out play so when you put the brakes on hard it makes a thump noise. when I bought the car the keeper was gone and the part that bolts to the half shaft just was sitting in the axle I replaced the keeper and the part that bolts to the half shaft back in 1986 the car had been stored a few years so I may not have noticed it when I drove it a lot. should I worry?
A common problem that causes loose fasteners is the front slip yoke. Make sure you check that the front slip yoke is free and lubricated.
Conceptually the transfer case and front axle are both bolted to the engine rigidly so a slip yoke shouldn't be critical in the front driveshaft. In practice it does a great job of eliminating vibrations and if it locks up you will quickly shake the bolts loose. I've had my front axle fall free because of it and I've gotten other Eagles for cheap because that happened to the previous owner. The CV shafts blow up and wipe out the front brake lines when it happens.