I had the same problem, turned out to be the control valve on the fel seems like there is a restriction or limiting device on the down side, which makes scence as you don't want the bucket free falling to the ground with a load on, I got around this by hooking up to the 4in one rams with a seperate control valve I mounted near the splitter ram, I tied the lever back with the bucket in the closed up position so the other valve was used to control the ram It was all plumbed up with quick connect couplings and extra long hoses 5/8" as thats what I had laying around, the ram is 3 1/2" dia with a 30" stroke, I also improved the spliting capability by mounting a back hoe bucket tyne over the standard wedge it's 2" wide and has a similar shaped wedge to the back, Iron bark,and our hard woods generally laugh at less than a 40t splitter, By the way this was done on a old CAT 428B backhoe with a rated 6500 lb front bucket loading.