Broke Hydrostat twice? Why?

[dfkrug]

After splitting the case, I first removed the motor (1st, 2nd photos). On first inspection, it
looked OK. The slippers looked smoother than I am used to seeing. Other HSTs
have pre-cut scratches in the slippers to help retain an oil film. I will check the
thickness with a micrometer later, after getting the spec from the manual.

I meant to report on the slippers, but I do not have a good close-up of the
pump slippers. I did mike them.

The manual has no spec on the slipper thickness, as I would expect, so I
just compared the thickness of those from the motor to those from the
pump.

They were the same. The pump slippers do have the pre-cut micro-scratches
that I expected to see on the motor slippers. This indicates to me that
none of the slippers had experienced significant wear.

Why the maker did not use micro-scratches on the motor slippers, I do not know.

 

[dfkrug]

Sure was cavitation, I was going ask how it was getting air but Roy posted the
reason.

Whether the proximate cause of the erosion of the valve plate was boiling or cavitation, which are very
similar, heat was a major factor.

Cavitation or boiling occurs when the vapor pressure of a fluid exceeds the ambiant pressure. Get any
fluid hot enough and it boils, even when the fluid is in a closed system under high pressure. In a
dynamic system with fluid flowing, any interruption in the flow causes lower pressure regions in the
fluid, sometimes resulting in bubbles of vapor to form locally (cavitation). Usually those bubbles
immediately collapse, which can cause damage to the surrounding surfaces of the fluid passages.

Cavitation can also occur at the inlet of any pump, as it attempts to move fluid by applying
low pressure to it. That is one of the reasons there in a charge pump to pressurize the
inlet on the HST pump. A pressure test by Bob's mechanic showed it was working.

The system RV, passing full flow of the implement pump at 2000psi, to the tank at 0psi ambient is
going to cavitate the fluid, as OnS says. After minutes of this abuse, the fluid in the tank is
going to probably aerate with all that agitation. Will the whole 5-7 gals of fluid get a bit foamy?
Possibly.

Entrained bubbles can even explode (Diesel) when pressurized by the system, if they
contain the right combo of oxygen and oil vapor. It is possible that the fluid was
dieseling at the high-pressure region near the valve plate. I suspect that dieseling
would foul the fluid rapidly.

But Bob reported that the loader still worked fine while he was experiencing loss of HST power.
Was it under-performing due to entrained air? Maybe, maybe not.

To me, that points to more localized boiling at the point of highest pressure on the fluid, at the
pump valve plate. Just my opinion. I welcome others, too.

 

[dfkrug]

So what about the broken spline, what does that indicate? Any part of cause
and effect on this particular HST, or is the manufacturer rebuilding used/broken/returned under warranty, HSTs
and selling them as replacement units, possibly?

I am scratching my head over the broken spline. The adjacent splines are fine. I suspect it just missed
QA at the factory.

 

[dfkrug]

It may be me, but I don't see the wear you refer to on the port(s) etc. I do see subtle scratches on some metals you
showed and some darkening of the metal discs in others. Can you possibly circle the exact areas you're referring to,
if not too much trouble, for us feeble minded older guys?:confused3:

See yellow dotted line.

When I refer to a "fingernail" test, if I can feel any ridge with my nail, that is a failure. Also used
with engine cylinder bores, cylinder heads, other critical mating surfaces, etc.

 

[Billrog]

dfkrug thank you for your time and explanations I now have a lot more knowledge on what actually goes on inside all I knew before was the caused damage just not what the damage actually was. I've ran tractors with the remote hydraulics engaged before but only for a min. or so until I figured out the reason for pour hydraulic pressure to the loader or transmission.

 

[dfkrug]

I've ran tractors with the remote hydraulics engaged before but only for a min. or so until I
figured out the reason for pour hydraulic pressure to the loader or transmission.

I suspect a newer tractor with a good engine and an implement pump RV set at 2000psi or less is going to bog
down less on relief, vs. a tired older machine with a tired engine.

When I operated my old Kubota with the 3-pt cyl valve at the top (on relief), it was very noticable. My
tired old rental tractor with 2000h on it really bogged down, so I did not use it that way for more than
maybe a minute. A minute on relief should not hurt anything.

That was my first tractor, back in the 90s, and I was a CUT newbie.

 

[oldpilgrim]

I cannot hear/feel my tractor FEL or BH go into relief. It just stops working.

If I drive into a pile of dirt that I can't move, it will either spin the wheels or stall the engine. I sense no relief at all.

 

[dfkrug]

I cannot hear/feel my tractor FEL or BH go into relief. It just stops
working.

If I drive into a pile of dirt that I can't move, it will either spin the wheels or stall the engine.
I sense no relief at all.

That is the HST relief, not the implement pump RV. The latter is set at 2000-2500psi, and
will only affect the FEL, 3-pt, and AUX valves. The former HST RV is set at 4000-6000psi, and
you may not feel it go into relief. I don't always on my tractor.

This is an important distinction. Bob's tractor saw the implement pump circuit go to relief, not
the HST pump circuit.

 

[dfkrug]

If I drive into a pile of dirt that I can't move, it will either spin the wheels or stall the engine.
I sense no relief at all.

In the case you describe, your HST RV is not opening. For that to happen, try driving into
that immovable pile in M or H range. THEN, tell us what you hear. If you are bogging the
engine, then turn up the revs to max.

 

[C4Ranch]

Great thread! I've always wanted to see inside of HST. May not fully understand how it works but thanks for this!

As the easiest failsafe, wouldn't plugging in a loop hose be simple and easy? No need for any lockout plates, etc.

 

[oldpilgrim]

this past winter, the fluids were very cold and the fel would react very slowly until the fluid got warm.

I read somewhere that if the bucket is put into full dump mode and held there, the relief would kick in and warm up the fluid faster as it squirted thru a smaller opening.

Is this true? It seemed to work. Is this a bad thing to do?

Very interesting thread.

 

[oldnslo]

this past winter, the fluids were very cold and the fel would react very slowly until the fluid got warm.

I read somewhere that if the bucket is put into full dump mode and held there, the relief would kick in and warm up the fluid faster as it squirted thru a smaller opening.

Is this true? It seemed to work. Is this a bad thing to do?

Very interesting thread.

FEL operating speed is a function of oil flow rate. If it is running slow from cold oil this is an indication that the pump is being starved of oil or cavitating. Running the pump at max pressure (over relief) will shorten the life of your pump considerably.

 

[oldnslo]

this past winter, the fluids were very cold and the fel would react very slowly until the fluid got warm.

I read somewhere that if the bucket is put into full dump mode and held there, the relief would kick in and warm up the fluid faster as it squirted thru a smaller opening.

Is this true? It seemed to work. Is this a bad thing to do?

Very interesting thread.

FEL operating speed is a function of oil flow rate. If it is running slow from cold oil this is an indication that the pump is being starved of oil or cavitating. Running the pump at max pressure (over relief) under these conditions will shorten the life of your pump considerably.

 

[GManBart]

FEL operating speed is a function of oil flow rate. If it is running slow from cold oil this is an indication that the pump is being starved of oil or cavitating. Running the pump at max pressure (over relief) under these conditions will shorten the life of your pump considerably.

The manual for my backhoe says that if the hydraulic light comes on, it means either the filter is plugged, or the fluid too cold. If it's due to cold temps, they direct you to put the loader into relief and hold it there for something like 15 seconds at a time, and do that several times, to heat up the fluid until the side of the reservoir is warm. I can't imagine they'd be recommending something that would shorten the pump life.

 

[Sysop]

There is nothing wrong with detented AUX valves....I need them for running
a backhoe, or a hyd PHD, or hyd concrete mixer. Mine is very hard to
accidentally engage. That's really the issue.

I like the solution on my tractor where it is a self centering valve, but they put a little hook on the platform of the tractor you can engage to hold the valve when using the backhoe or something requiring full time flow.

 

[dfkrug]

The manual for my backhoe says that if the hydraulic light comes on, it means either the filter is plugged, or the fluid too cold. If it's due to cold temps, they direct you to put the loader into relief and hold it there for something like 15 seconds at a time, and do that several times, to heat up the fluid until the side of the reservoir is warm. I can't imagine they'd be recommending something that would shorten the pump life.

That's interesting. Does CASE recommend that procedure for the 580?

Of course, running the implement pump circuit on relief will warm up the oil, fast. But sucking cold oil into
the pump can cause cavitation, as OnS says. I have not seen that recommendation in any tractor manual
I have read, and I do read them. They all recommend letting the tractor warm up for a while before
using it.

My tractor when cold (50F or so) protests when I try to put much of a load on the HST too soon. A light
on the dash comes on that looks like a horizontal squiggle with circle around it when I use the go-pedal
too soon up even the slightest grade. It comes on steady, or flashing. No info on this light in the OM at all.

In terms of manufacturer recommendations, I remember reading a Caterpillar manual for an early 30s Cat
28 dozer. It recommended lighting a fire under the engine to help with warm-up. Wow.

 

[DavesTractor]

This is a great thread. The OP is a customer any dealer would want. Yes, dealers have good customers and not so good, just like customers have good dealers and not so good.

Of course this is already solved by people more knowledgeable than I, but we cannot over emphasize the amount of heat generated in a system that is bypassing. One formula I saw is BTU/HR = 1.5 x PSI x GPM. PSI is the difference in pressure from the relief valve to where it is going, the tank in this instance. Relief should be around 2400 PSI in most small tractors. GPM is the pump flow I think, maybe 5 gallons on this tractor at 2000 rpm. Do the math and you get 18,000 BTU/hr. Lot's of heat.

Keeping the oil cooler clean is important. Making sure the relief is not open due to a remote in detent is critical. I like the ideas mentioned of securing the lever, but also putting a loop hose in just in case. Great idea. Finally, installing a heat gauge in the tank would also be smart.

 

[dfkrug]

Keeping the oil cooler clean is important. Making sure the relief is not open due to a remote in detent is critical. I like the
ideas mentioned of securing the lever, but also putting a loop hose in just in case. Great idea. Finally, installing a heat
gauge in the tank would also be smart.

I have no problem with any of those methods to avoid this problem. There are a lot of ways to break a tractor.
I especially like an oil temp gauge cuz that is always working and does not require any special procedure to
avoid putting a RV into more than momentary relief. It also guards against other things that could raise temps.
It also could tell the operator when it is OK to do some work (oil warm enough).

From your perspective as a dealer carrying more than one brand, Dave, do any of them sell internal parts of
their HSTs?

(BTW, I told Bob to stop by your place to oogle new tractors if he decided to take the I-5 (faster) route home.)

 

[DavesTractor]

We can show Bob some cool tractors. We have a DF tractor here that is just a little longer, but no wider or taller than a 30 HP Mahindra and it is 96 HP. Made for vineyards or orchards. Dangerous to stop here though, it often causes one to buy a new tractor!

Our OEMs do not sell HST parts. Just complete units.

 

[Coyote machine]

I second the let it warm up to temp thinking instead of, even if recommended by a manufacturer, idea of throwing the system into relief as a way to raise the trans fluid temp. From my perspective, I want a long life from my tractor, so giving it a few minutes to come to operating temp is time well spent doing a walk around to see if there might be something that might need attention, low tire pressure, torn or leaking hose, etc.

And consciously putting a HST into relief to bring oil temp up is not likely to do any real harm, partly because the oil is already cold and will have to get to temp to do it's tasks. BUT the accidental knocking a lever into relief, likely when the oil is already at operating temp is a whole different situation, especially if it is left in relief for unknown, possibly extensive amounts of time. Relief is just that, something that is meant to protect, not meant as a means of pulling excess heat constantly.

I hang my 'loop hose' near where my tractor sits, and whenever I remove my backhoe it goes on to protect the circuit from overloading the HST. It's cheap and easy 'insurance' against what could otherwise be a very expensive failure. YMMV.