We have one of these machines and it was in a similar state when I started here five or so years ago. So yes. First of all it is critical that the spindle is unclamping consistently and that can be a combination of the air over hydraulic cylinder not functioning properly, or the the hydraulics in the spindle leaking (top of cylinder not sealing properly or loose. After that there are two issues that can mess up a tool change. The big one are the cam followers on the indexing plate on the tool changer. Take the cover off and take the end guard off of the tool changer motor. Take the fan off the motor and use a small set of vise grips to rotate the motor by hand. Looking down from the top the cycle starts with the limit switch cam on the lobe. You can slowly cycle the changer through the stroke (empty). The changer arm attaches to the shaft via a tapered style lock ring. You get to it by removing the finger lock on the bottom of the changer shaft. There is a spring and an E shaped lock that should slide easily in and out by gravity. This locks the fingers in place while the arm is in transit so the holders don't fly out The locking mechanism is then pushed out when the tool changer shaft lifts, allowing the fingers to let go. If a cam follower is broken or bent on the index plate this can affect the end position, so indexing the unit through a couple changes and inspecting the cam followers when they become disengaged from the plate, then adjusting the arm position by loosening the taper lock screws, adjusting position, and then locking them down once the arm is in place. In Home position this should be parallel to the edge of the tool changer base plate. So, if the oil level is low in the charge cylinder the spindle will not fully release and the result is that the the changer finger will likely bend or break when trying to pull the tool out of the spindle resulting the the tool dropping out of the spindle once it's fully released because the holder can't hold it. Changing the tool manually isn't a good indication of what kind of shape the release is in as there is no time limit on a manual clamp/release like there is on an automatic tool change. The spindle clamps the tool via a stack of belleville washers and releases when the hydraulics compress those washers. This results in a fail-safe condition of the tool being clamped by default when there is no power or hydraulic pressure present.
Hope this helps.
