HST Problem Solved?

[jerkyboy]

So I took my HST apart and found that the bottom of the cylinder block on the pump side scored the port block (not sure if that's what its called) pretty heavily and the cylinder block on the motor side scored it, but not nearly as bad. Otherwise, the inside of the HST looked fine. I've attached some photos but would love to know the cause.

 

[crazyal]

How many hours are on your BX? Did it have the filter and fluid changed when recommended by Kubota? I had a service man tell me that the HST is much more sensitive to anything in the fluid than the hydraulic pump.

 

[jerkyboy]

It has 480 hours and the fluid was changed at 3xx with a Kubota filter and their SUDT2. All fluid changes have been done per factory recommendations.

 

[Deano]

Wow, that doesn't look like 480 hours...very interesting. Did you cut open your filter and see if anything is abnormal?

Deano

 

[Yandaddy1110]

I had my hst backing plate resurfaced and I replaced both pumps.

 

[jerkyboy]

Wow, that doesn't look like 480 hours...very interesting. Did you cut open your filter and see if anything is abnormal?

Deano

Not yet, but I will and post the results. When I took out the tranny screen and saw metal filings I figured something was up.

 

[jerkyboy]

I had my hst backing plate resurfaced and I replaced both pumps.

Just like having a flywheel resurfaced.:thumbsup::thumbsup: Great idea, I didn't think of that but I've already got a new HST on the way. I just need to figure out what caused it so it doesn't happen again. I'm thinking of replacing the priority flow valve per mattj's suggestion from another post.

 

[oldnslo]

So I took my HST apart and found that the bottom of the cylinder block on the pump side scored the port block (not sure if that's what its called) pretty heavily and the cylinder block on the motor side scored it, but not nearly as bad. Otherwise, the inside of the HST looked fine. I've attached some photos but would love to know the cause.

Do the surfaces look pitted at all or just scored?
What did the slippers on the pistons look like?
Was there any scoring or marks on the swash plates? I.e. Slipper wear plates

Since these are "closed loop" usually when one component (pump) starts to wear it puts the trash into the rest of the components (motor).

Do you use this for plowing snow in the winter? FEL, blade, or blower? Does it sit in a cold building or heated building?

Do you use it mostly for mowing lawns or lots of FEL work.

Just trying to get a feel for use which may help narrow down some possible causes.

Roy

 

[Texas Fella]

You should not have the port block (yes, that is the correct term) "resurfaced", just not a good idea. Just looking at the pictures, it looks as if the charge pressure for the system was low. But I admit that it is strange to see that type of damage on 1 side only. On the BX, the charge pressure is created by the main hydro pump (if I remember correctly) and a regulator valve the splits oil off to steering, pto, and hst. I would check the charge pressure after reassembling.

 

[jerkyboy]

Do the surfaces look pitted at all or just scored?
What did the slippers on the pistons look like?
Was there any scoring or marks on the swash plates? I.e. Slipper wear plates

Since these are "closed loop" usually when one component (pump) starts to wear it puts the trash into the rest of the components (motor).

Do you use this for plowing snow in the winter? FEL, blade, or blower? Does it sit in a cold building or heated building?

Do you use it mostly for mowing lawns or lots of FEL work.

Just trying to get a feel for use which may help narrow down some possible causes.

Roy

Not sure what the slippers on the pistons are. I did a pretty thorough look over of the internals and that is all that I noticed but I'll check again later this week.

The prior (original) owner did use it every winter for snow blowing. He also had it dealer serviced (I have all the receipts) during his ownership. The tractor does sit in an unheated garage, but mine is very well insulated and does not typically go below 30 degrees.

I use it mostly for mowing and I have the Kubota leaf system, which I use extensively in the fall. The problem started happening when I was moving crushed stone (6 ton) and leveling out a small area with the FEL.