Broke Hydrostat twice? Why?

[oldpilgrim]

when I referred to 'cold' in my post about making it to go into relief to warm it up, I was referring to winter cold, like teens or below. At plus freezing, the hydraulics are only sluggish and I never felt the need to 'relieve' them.

Would those temps be more or less likely to cause damage.

 

[GManBart]

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.

Luckily Case doesn't recommend any fires! Yes, for both the 580 L and M series (only two I'm familiar with) they recommend rolling the bucket back until the pump goes into relief, holding it there for 15 seconds, then repeating until the reservoir feels warm to the touch.

 

[MinnesotaEric]

Good photos of a failed GST unit, MHE.

Back when I repaired my Kubota B21, purchased with a bad transmission, I was able to get a quotation
for the HST pump or motor separately. But components of each were not sold separately; the pistons
were all "matched" to the cylinder blocks. I do think that any bad pistons with slippers should have
been replaceable separately, as long as the bores were in spec. Even in a case like yours, as you say.

I did end up buying the charge pump separately cuz the rotor and block showed some wear. In that
HST, the charge pump is on the front of the HST. Other HSTs have it separate.

I'm just getting back to this thread. Aren't hydro motors like ring and pinion or planetary gear sets that wear into each other, and because of the unique wear patterns must be replaced as an assembly or face certain doom?

I know there was a big lawsuit against a supplier over planetary gears in rebuilt UH1 and AH1 transmissions because the contractor cheaped-out and replaced individual gears rather than using all new planetary sets that led to a bunch of failures and several deaths. Years ago in both my Army and civilian tech schools, the instructors were adamant about replacing gear sets.

 

[MinnesotaEric]

While working today (with rest breaks for both me and the tractor) I noticed something disturbing.

I have a frame mounted backhoe. It is usually not attached. There is a lever that comes out from under the front of my seat that operates the rear remotes. The lever moves either way sideways and has a detent position at its full travel point. It is possible when entering or leaving the tractor to brush up against the lever and if you do it hard enough, it will stay at its full side detent position. I've noticed this before and I just re center the lever. There is no strange sound or any thing.

But now I'm more alert for any thing odd. How often have I NOT noticed this? There is no telling.

So I tried something. While traveling down the driveway at 2200 RPM, I moved the lever over to full detent. Tractor immediately bogged down by about 200 rpm. No hydro noise. No relief valve noise. No change at all except losing 200 RPM. Since the lever can only be accidentally moved while entering or exiting the tractor, I would never notice the missing RPMs. I would just start it and adjust the throttle.

More and more I'm thinking this is an overheat thing. Sometimes too low RPMs, sometimes the wrong gear, sometimes dirty oil cooler, no temp guage, and now this.

MHE's very helpful post - particularly those graphs - tell me that it is possible to ruin a hydro over a fairly long time without burning or even dis coloring the oil.

Well, tomorrow Jordan is going to mail me the old hydro and my wife and I are going to drive it down to DKrug as soon as we can schedule it, and then we'll all know.

I had a weird happening with one quick disconnect popping off. The only way to connect reconnect my QD again, was to set the detent lever to open the valve and then force the coupling together enough to bleed off the pressure. Course, after all that fiddling, twice I forgot to move the detent back to center before starting the tractor. At idle, cold and my 60hp tractor would start, fight to run, lose, and die. Warm, and the no stall was able to keep the tractor running at idle. I noticed the pressure relief noise immediately both times and corrected in seconds. However, at anything above idle, my tractor would easily have enough power to bake its bits until Kingdom come.

 

[JohnMacca]

Great thread for a newbie! It makes enjoyable reading, especially when there is no hint of preaching, just a desire to help people understand their equipment :thumbsup:

With my CK35HST, both the sales guy during the delivery walk around and the mechanic doing the free first service warned of the danger of engaging the AUX lever with nothing attached to the remote. They called it "deadheading" the pump and demonstrated the slight drop in revs and how the machine sounded to be straining. They didn't go into a lot of detail but said it was something to be aware of because you could do some serious damage without knowing. Now I know why.

Thanks again for taking the time to make TBN a great forum.

 

[dfkrug]

Aren't hydro motors like ring and pinion or planetary gear sets that wear into
each other, and because of the unique wear patterns must be replaced as an assembly or face certain doom?

That's one of the cool things about HSTs; no gears!

You are prob thinking about conventional automatic trannies on cars and trucks. They are a complex set
of wet clutches, planetary gearsets, wet brakes, and spool valves. I saved some parts from an 80s
4-spd Ranger AT I took apart, and it must have had 20 spool valves in it! These units are WAY more complex than
an HST. They are the 2nd most complex element of your auto, after the microprocessors, IMO.

Although, I do not like brand-bashing (there is something good about all brands), I really like how
some of the majors sell HST internal parts, and it seems NONE of the 2nd-tier brands do.

 

[Bob Christensen]

OP here. I'm back home after a really beautiful drive down and back on the coast highway from northwest Washington to just south of Big Sur. Just wow!

The visit with Dkrug was very satisfying indeed. I am sure he is right in his analysis (it was fascinating to watch that analysis develope through the postmortem).

It is now my responsibility to use the knowledge gained here to change my methods/habits so that there is no repetition for me and perhaps avoid such failures for others who read this.

The way I see it, the cavitation was caused over time by oil thinned by excess heat. The likely culprits and remedies are :

The rear remote detent lever. It is almost certain that the tractor ran for extended times with the lever pushed over into full detent position, deadheading the oil flow and creating heat. This process is particularly diabolical because it would have to happen as I climb onto the tractor, sometimes brushing the lever over into detent - then starting the tractor and not noticing the slight lowering of RPM and slight straining of the motor. No relief valve sound to my ear.
So I can't be sure how often or for how long this happened.
Anyway, it won't happen again. I will devise a way of locking it into neutral position and if I have any doubt at all of its effectiveness, I will have a quick connect hose made as described by others.

I will be more conscientious about cleaning the oil cooler.

I will install a temp guage. I'm not sure how yet, but I'll learn.

I will fix the front grill. It won't be pretty.

I will pay more attention to RPMs in future, using more when there is more work to do.

I will lean towards using low gear more often.

I will not use cold weather oil.

Please feel free to add to or modify anything on this list.

I must say it is humbling to find so many errors in my procedures, but if you look at my Original Post, that is just what I was asking for.
I never dreamed that I could get so much specific help, or that it could be so much fun in the process.
I thank you all.

Bob

 

[Bob Christensen]

Double post

 

[dfkrug]

Here are a couple of photos that Susanne took. One is a better look at the broken
spline on one of the shafts.

 

[dan268]

OP here. I'm back home after a really beautiful drive down and back on the coast highway from northwest Washington to just south of Big Sur. Just wow!

I will install a temp guage. I'm not sure how yet, but I'll learn.
Bob

Very interesting thread. Bob, did you ever install the temp gauge? If so, can you post some pictures and explain what you did? The transmission on my Kubota BX2200 just died and when I get it fixed (probably by the local Kubota dealer), I'd like to install a temperature sensor.

-Dan

p.s. Sounds like a lovely drive. My wife and I are planning to do that this summer to visit family.