Hydraulics pause when lowering blade into ground?

CAT D3B with 6 way blade...
When I lower my blade to the ground, there is a noticeable 'stop' or 'delay' to the blade, before it starts to apply down pressure. The easiest way for me to describe it is: Let's say I wanted to lift the front end of the machine up in the air but my blade was all the way raised. I would lower my blade, then when it hits the ground, it stops lowering, and after about 4 seconds of holding the stick, it continues to lower and starts to lift the machine up.

This makes it obviously more difficult to carry a steady grade.

What is the most likely cause of this? Where should I look first for troubleshooting? I'm not very experienced with dozers.

It has open centre hydraulics, so when a load is met, the system has to develop pressure before it goes further. This takes time.

Open centre = flow is continuous and pressure is intermittent.

Closed centre = hydraulic pressure is continuous and flow is intermittant.

.RC. said:

It has open centre hydraulics, so when a load is met, the system has to develop pressure before it goes further. This takes time.

Open centre = flow is continuous and pressure is intermittent.

Closed centre = hydraulic pressure is continuous and flow is intermittant.

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Although yes, it is an open center system, I don’t believe this is the cause. Would there be another reason?

Piston said:

I don’t believe this is the cause. Would there be another reason?

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What you describe is somewhat typical on a system such as you have. Without actually being there and observing the reaction of the blade it's impossible to judge if your machine is normal or worse than it should be. 4 seconds does sound like a long time
Amongst other possibilities could be a worn pump, cylinder seals leaking, a loose cylinder piston, etc, etc.

Nige said:

What you describe is somewhat typical on a system such as you have. Without actually being there and observing the reaction of the blade it's impossible to judge if your machine is normal or worse than it should be. 4 seconds does sound like a long time
Amongst other possibilities could be a worn pump, cylinder seals leaking, a loose cylinder piston, etc, etc.

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Do you mean typical because it’s an older dozer? I’m just surprised it would be this extreme. None of my other open center machines that I’ve had over the years have acted anything close to this, I’ve never noticed enough of a pause to think anything was abnormal. However, I’ve also never had a dozer before so perhaps it’s just with dozers, but I can’t understand why.
It’s hard for me to see what is happening because I don’t have anyone to raise and lower the blade while I watch it either.

i can deal with it the way it is, I’m only using it as a homeowner and do my finish work with a tractor, but it is an annoyance and if it could be fixed I’d be interested in making it right.

Look at the linkage where the blade is hooked to the C frame .
Check where C frame is hooked to tractor.
Bet it's wore out or pieces are missing.
Bob

4 seconds is too long but a slight delay is common. Wear in pivot points could add to the problem but still think 4 seconds is too long. If the blade is left in the air does it creep down after you shut the machine off?

Welder Dave said:

4 seconds is too long but a slight delay is common. Wear in pivot points could add to the problem but still think 4 seconds is too long. If the blade is left in the air does it creep down after you shut the machine off?

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I’ll have to try that, I’ve never left it in the air to see.

It would/could indicate if the piston seals in the cylinder(s) were leaking.

Most dozers cavitate during full speed blade lower. That means the oil exits the cylinder rode end faster than the pump fills the head end. The cylinder area ratio works against you here also. The delay is the pump catching up to fill in the empty void in the head end of the cylinders. Try the test lowering the blade at slower speeds. If you reach a point where it no longer happens, that will verify what is going on. Typically you don't notice the spongy cylinder because the cutting edge puts down pressure on the blade causing it to dig in. It usually shows up on hard or rocky ground where the cutting edge rides up over the rock/hard material.

Anti-cavitation valves help by filling in the cavitation even if you aren't commanding a blade lower, but not every valve has them and they aren't always real effective.