450 C Blade valve

blade has downward drift. Can the valve be rebuilt . I have already had the arm cylinders packed. If so where could I have this done?

Yes, valves can be rebuilt, but results depend on what is worn and if parts are available. You might end up replacing the valve. A dealer or good hydraulic shop should be able to do it. Drift is often a cylinder problem, new packings can be damaged at installation. Not saying that is your problem, but is a possibility.

More info may help. What is the brand of your machine, John Deere and Case both had 450C models. In some cases there might be other things to check particular to a brand. You had the cylinders packed, one would assume trying to remedy this drift. Is that correct? If so was there a change in drift rate after the cylinders were packed? Is this a 4 way or 6 way blade? Any idea of hours on the machine? Single or multiple lever control? Is the linkage free? If you carefully move the lever can you get the drift to stop? Does the lever center itself when you let go of it or do you have to move it to neutral? You say the arm (lift?) cylinders were packed. Where were those done? Were OEM packing materials or aftermarket fit matched?

I know this answer is more questions than answers, but having all the info possible helps.

Drive up to a tree stump or the like and lift the front of the dozer up and see if it will hold,if it holds the issue may well be in the valve as the piston in the cylinder has only the one seal sharing both up and down,if it does not hold it is more than likely a cylinder,it only takes one to be leaking to cause the blade to drift,If the dozer is JD it would be unlikely the seals got damaged on installation, but very likely with the Case,it has a groove to carry a square backing ring and if that ring gets twisted during installation you will have an internal leak,the outer pressure ring is often stretched too much and gets caught in the thread of the barrel when installing the rod,care and experience is needed with the Case setup,about the valve,it is very seldom a valve will need service,they are supposed to be working in clean oil and unless something fails in the system it is unlikely it is the cause of the problem,if the valve feels normal and returning to neutral position and has no leaks I would leave it alone.
AJ