Hydrostatic diagnostics

Futbalfantic

Well-Known Member
Joined
Aug 5, 2006
Location
Charlotte
I have a Lesco Z-two Z turn mower and the right side hydraulics are on the blink. When the left stick is pushed/pulled full value the motor lurches but does not apply significant power. After getting it to move it travels OK but not at full power or speed. I’m guessing there is blow by in either the pump or the motor.

it is a dedicated pump system with both sides having a pump.

How do I go about figuring out if it is the pump or the motor. Are these things rebuildable? Really not looking forward to having to drop $700 on a new pump/motor
 
Since this is a split system, there is unfortunately not a good way to see which part is failing without a hydro test kit, but we'll see what we can do. I have to ask a few questions first. How many hours on the machine? What's the hydro oil level? When was the last hydro service? What's the condition of the drive belt? What about the drive pulleys? What does it SOUND like, i.e. is that side screaming like a 70s Ford power steering pump that's low on fluid? Any leaks?

Make sure that the bypass valve is not open at all. It should be the fitting on the pump that has a hex head with a hole drilled through it. DO NOT CRANK IT DOWN, just see that it is seated.

That's about the extent of it without having a hydro test kit and not being there to personally see what's going on. There are relief valves that should be externally accessible, but without knowing which pump you have, I'm not going to say remove them.

When the pumps fail internally, it's usually cheaper and wiser to replace them instead of rebuild them. Same story with the wheel motors. The wheel motor is "less likely" to have failed since it is a less complicated device than the pump. With that said, depending upon what actually is wrong, there is a chance that if the pump failed, it could have wiped out the wheel motor as well.
 
So turns out it was just a stretched belt. Runs like a champ now (minus all the other neglected stuff).


maulcruiser said:
Make sure that the bypass valve is not open at all. It should be the fitting on the pump that has a hex head with a hole drilled through it. DO NOT CRANK IT DOWN, just see that it is seated
Click to expand...
So what if that fitting is super sticky and quite impossible to turn without force? Not sure if I’ve cranked it down or if it just wouldn’t turn.

what entails a rebuild of a pump. Guessing way more than just replacing seals. Just hard to swallow $700 for a pump
 
My apologies on the late response. I've been on vacation the past two weeks.

Happy to hear that it was simply just a belt that was worn!

That fitting, unless it has a bolt through it to be used as a handle, is typically sticky. I've never had one I could turn without a bolt or a wrench to get it unseated. After that, they "should" turn fairly easily.

A pump rebuild is a plethora of possibilities. It could simply be a reseal, or it could get down to replacing hard parts. A visual inspection of the internals will typically reveal most of the issues. If there is ANY scoring that can be felt with a fingernail between the pump rotor and the base, it should all be replaced. In these pumps there are typically 5-6 pistons in the pump rotor (think of it as a revolver and the ammunition is a piston) and each piston usually has two springs inside of it. If these springs are broken or soft, they should be replaced. The swash plates can wear. These look like half of a crankshaft bearing. There are also the relief valves that can stick or become too soft. That's pretty much all of the points of failure. In the grand design, these are very simple devices with few moving parts, but the parts that do move need to be precise and clean. Simple lint from a rag could potentially score the pump rotor faces.

I say all of that to finish with you needing the specifics for your pump to know if it needs to be fully rebuilt or replaced. There are measurements that can be taken on the springs to see if they have failed. With all of that said, it's typically more cost effective to replace it than to rebuild it.
 
Thanks for the reply! So the one pump the T-bolt is still in place and once I break the seal it is easy to turn with minimal effort. The other pump the T-bolt is missing and it take pretty good force with a wrench to turn.

With a new pumping being $7-900 I feel like the break down and checking the pistons and the swash plate and replacing the seals and springs would be cost effective solution.

The biggest concern, since replacing the belt fixed the slipping, is the bypass bolt being such a pain to turn. Can that cause pump problems and is it something I should address to prevent pump damage?
 
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