Sounds like you have air in the Hydraulic line. There must not be air because air will compress and it will do exactly what you described. To remove the air make sure your hydraulic fluid is full. Then cycle the ram a few times. Do not try to split yet. Do this again few times and top off the fluid again. When all the air is removed from the lines It will work properly.
Answers & Comments
Sounds like you have air in the Hydraulic line. There must not be air because air will compress and it will do exactly what you described. To remove the air make sure your hydraulic fluid is full. Then cycle the ram a few times. Do not try to split yet. Do this again few times and top off the fluid again. When all the air is removed from the lines It will work properly.