1988 machine with 14K hours. Semi U blade. Is there an adjustment for the "down" feed of the blade ? If you ease the control you can walk the blade down . If you use any swift motion the blade just drops and slams the ground. This issue has been getting worse as I run it so there is something wearing or something coming out of adjustment. Thanking you guys in advance, I love this site !
Push the control lever slightly forward from the centre (hold) position and the hydraulics should power down the blade. In other words it'll lift the tractor off the ground. Push the lever further forward past the detent and you are in float. The blade will come down with a crash. I'd suspect wear and/or maladjustment in the linkage between the lever and the valve. With the blade on the ground and the engine off try pushing the lever gently forward from the centre position. Can you feel the detent..? if not then that's where you need to be starting to look. Also when the machine is at normal operating temperature do the lift cylinders drift down slowly under the weight of the blade..? If so how much..? Serial Number prefix always helps. There are a million & one different D6H models.
Sorry Nige, 3ZF00730 I will probably run the machine back in the shop today and remove the cover plate around the control to have a peek. No work today, it is about 2 degrees and blowing 20+ mph. If the blade is in the up position and the machine is off it will drift down ever so slightly about once a minute or two. If the blade has the front of the machine lifted up (to help clean tracks) then it will drift down at a slightly higher rate.
That sounds fairly normal. The cylinders aren't really designed to support the machine so it creeping down if you use the blade to lift the front of the machine is certainly not unexpected. Regarding downward creep with the blade in the air I'm not sure what the specification is for a "good" (i.e. not leaking excessively past the piston seals) cylinder, I'd guess probably about 1-2" of rod movement in something like 5 minutes with the hydraulic system at normal operating temperature. As above try finding the detent on the blade control lever first and report back if you can feel it or not.
OK, I did not get the machine back in the shop today but I was able to run it for an hour or so.... BRRRRR!!!!!!. The detent is there but the blade will fall well before you get against the detent, or past it. So in other words this is not the "float" dropping the blade. The linkage is clearly worn. If you do go foreword through the detent the control handle is darn near touching the front of the opening in the cover plate.:Banghead
It is more likely you are having issues with your quick drop valve. They are located on the end of your lift cylinders. You may have a broken spring, they can also be adjusted by adding or removing shims. Add shims to decrease sensitivity, remove shims to increase sensitivity. Weight (frozen dirt on the blade) also affects quick drop operation
I need more information on this "quick drop" valve. I will search my books tonight. Thanks Ron
It may be located on top of the grill between your lift cylinders
On my H one of the lift cylinders had a a cracked piston that fits at the top of the lift cylinder.There is a spring loaded plugger that was also stuck.They are for the quick drop and inside the top of the lift cylinders.Had to block off each cylinder at a time to find which one was bad.Good luck