Uni. Joint Problem 2
There are two possibilities here.
One is the cap is not sitting down in the U shape of the yoke.
The other is the caps won't come together enough onto the u-joint itself.
If the caps won't fit the U shape then they are too large or you need to clean the seat out in the yoke.
If they won't come together then you might have a pin on it's side under one cap or both. Sometimes the seal on the cap can be a bit hard also which will hold the caps out too far.