I have a 1989 Cat 426 backhoe with a tilting issue on front bucket. All rear hydraulic functions perform as they should and front boom lifts as it should. Also the dump function will raise the backhoe off the ground at idle throttle when bucket is on the ground but will not tilt up. I've tried the working another function while attempting to curl the bucket but that has no affect on it so I'm assuming it is not resolver related. Also, since the valve allows the dumping part to work then I 'll also assume the compensator spool is not stuck which would shut off hydraulic fluid to the main spool which would not allow the dumping part to work. When I raise the front boom, the bucket will not hold it's position and will just tilt down with gravity until it is in the full dump position. Could this be a relief valve stuck open on the curling side of the valve allowing the hydraulic fluid to bypass and not reach the cylinder? Any help would be appreciated. Thanks.
Sounds like you might have a piston come off the end of one of the rods. Disconnect the hoses from one of the cylinders, cap them and leave the cylinder ports open. See if it will work on one cylinder. Repeat for the other side if necessary.
The Cat 426 has only 1 dump cylinder.
Depends on the series, but yes, the first series 426 has only one. The theory of the loose piston still applies though.
Actually, forget that. The single cyl tilt mechanism works the other way round. My bad.
To eliminate the cylinder as the problem, swap the hoses around and see if the problem goes the other way.
Thanks for the replies. I will try swapping the hoses as you suggested and report back. Thanks again.
Swapped hoses and now it will curl inward under pressure but will only dump by gravity. I guess that rules out the cylinder. Must be something in the valve that would only affect half the valve since the other part is working. Any other ideas to try?
The problem is possibly in the line relief valve for the head end which will be item 14 at the bottom of the picture. If you remove it and can't see anything obviously wrong, try exchanging it with the other line relief valve at the top and see if the fault goes the other way. From memory, these are not easy to get to.
Does the spool move the same distance each way as the loader boom spool? I can't figure out that diagram, and I'm not familiar with Cat valves, other valves will block movement in one direction from debris inside the valve, broken springs, or oil built up in the cap on the bottom of the spool.
Thanks for everyone's help. Finally got around to pulling the relief valve out yesterday evening. It was noticeably stuck open. I swapped it out with a spare relief valve that I had and now the tilt function is working as it should. Thanks Again!!
where is the relief valve located????
re read Cmark's post #9 above. #14 in the diagram. On the side of the hose that goes to the function in question.