BX23 HST Oil Leak

[rScotty]

I've been able to confirm what I posted above. This is a 3/4-16 UNF threaded opening, not tapered.

Good. It would have been poor form to cross-thread that opening at this stage in the game.

I have found out since the other day that the old B7100HST tractors (vintage 1977-1984) used a HST charge filter in that same top of the HST case position that was a 10 um (0.0004") filter and mounted with a 3/4-16 UNF thread. So your BX may do the same. Some Work Shop Manuals do mention that thread specifically, so apparently that filter is special that way. The filter may even have a male thread??

I've no idea why my M59 transmission filter is threaded differently.
rScotty

 

[rScotty]

Sorry to hijack the thread, but a related question: Are these hydrostatic transmissions "flooded" with just an overflow back to the tank/sump/reservoir/transmission casing?

TIA

I don't know about all HST transmissions....or for that matter about the BX in particular.
If anyone has a BX Work Shop Manual, it will be in there.

But in general, HST transmissions could use their own separate enclosed "flooded" oil system...., but we could spot the ones that did pretty quickly because a separate HST oil sump would also need its own separate cooling system & radiator. HST trannys make a lot of heat.

In the past I have looked at the old B7100HST( post 1977) as well as the B6200HST, B8200HST and the modern HST+ tranny by Kubota. In all of those the HST shares a common sump and common oil with the rest of the hydraulic system. All of those do have an extra very fine filter specifically for treating the HST oil before it goes inside the HST itself.
Enjoy,
rScotty

 

[dicktill]

I don't know about all HST transmissions....or for that matter about the BX in particular.
If anyone has a BX Work Shop Manual, it will be in there.

But in general, HST transmissions could use their own separate enclosed "flooded" oil system...., but we could spot the ones that did pretty quickly because a separate HST oil sump would also need its own separate cooling system & radiator. HST trannys make a lot of heat.

In the past I have looked at the old B7100HST( post 1977) as well as the B6200HST, B8200HST and the modern HST+ tranny by Kubota. In all of those the HST shares a common sump and common oil with the rest of the hydraulic system. All of those do have an extra very fine filter specifically for treating the HST oil before it goes inside the HST itself.
Enjoy,
rScotty

Hi rScotty,

Was hoping you'd reply. When I said the hydrostat may be flooded, I did not mean that it was its own sump, nor that there was a separate pump for it. On "Fergie", as far as I can tell from factory manuals, parts books, and especially some photos of individual components I found on eBay, it appears that there is one input to the hydrostatic transmission. The hydraulic schematic (which is quite similar to the Kubota BX) shows a low-pressure internal relief valve set at 57-85 psi, dumping back to the tank. There is also a high-pressure relief valve between the two sides of the pump-motor connections set at 2554-2700 psi. Going back to the eBay pictures there only appears to be one connection (near the top) back to the tank. I am guessing that the hydrostatic transmission casing is always flooded with this one connection being an overflow, and that the low-pressure relief valve as well as any motor and pump leakage just dump inside the casing and then eventually through the overflow. Does this sound correct? And if it is, then when I do a hydraulic system drain and refill, should I also pull one of the plugs on the bottom of the hydrostatic transmission to drain that?

Thanks, Dick

 

[rScotty]

Hi rScotty,

Was hoping you'd reply. When I said the hydrostat may be flooded, I did not mean that it was its own sump, nor that there was a separate pump for it. On "Fergie", as far as I can tell from factory manuals, parts books, and especially some photos of individual components I found on eBay, it appears that there is one input to the hydrostatic transmission. The hydraulic schematic (which is quite similar to the Kubota BX) shows a low-pressure internal relief valve set at 57-85 psi, dumping back to the tank. There is also a high-pressure relief valve between the two sides of the pump-motor connections set at 2554-2700 psi. Going back to the eBay pictures there only appears to be one connection (near the top) back to the tank. I am guessing that the hydrostatic transmission casing is always flooded with this one connection being an overflow, and that the low-pressure relief valve as well as any motor and pump leakage just dump inside the casing and then eventually through the overflow. Does this sound correct? And if it is, then when I do a hydraulic system drain and refill, should I also pull one of the plugs on the bottom of the hydrostatic transmission to drain that?

Thanks, Dick

That's interesting. I see what you mean by "flooded" now. No, I don't know off the top of my head whether Kubota is built that way or not. Or if they all are.

But your explanation does explain why some of the early Kubota HSTs exploded diagrams seemed to show an extra relief valve where the relief leads to an internal passage.

I also wonder if all HSTs use a dedicated HST charge pump and filter like Kubota does? Does MF?

The reason I ask if the Massy Fergie hydrostatic transmission has that second super fine filter mounted inline with the HST charge pump is to give my best guess at answering your question about draining the HST during a fluid change.

Here goes.....My guess is If the HST has that second super fine filter (10 micron) in line with an internal HST charge pump, I would NOT drain the HST when doing a hydraulic system drain and refill. I just cannot see it being necessary.

But if the HST relies on hydraulic oil that is only filtered by a single typical screw-on hydraulic filter (often a 30 micron) - then I WOULD drain the HST when doing a system fluid change.

The nice thing about the systems that have the two screw on filters - the 30 and the 10 micron - is that eventually all of the trans/hydraulic oil passes through the finer filter. In that way the HST charge pump and fine filter act like a "bypass" or "polishing" filter for the entire trans/hydraulic system. That's a nice bonus..

rScotty

 

[dicktill]

That's interesting. I see what you mean by "flooded" now. No, I don't know off the top of my head whether Kubota is built that way or not. Or if they all are.

But your explanation does explain why some of the early Kubota HSTs exploded diagrams seemed to show an extra relief valve where the relief leads to an internal passage.

I also wonder if all HSTs use a dedicated HST charge pump and filter like Kubota does? Does MF?

The reason I ask if the Massy Fergie hydrostatic transmission has that second super fine filter mounted inline with the HST charge pump is to give my best guess at answering your question about draining the HST during a fluid change.

Here goes.....My guess is If the HST has that second super fine filter (10 micron) in line with an internal HST charge pump, I would NOT drain the HST when doing a hydraulic system drain and refill. I just cannot see it being necessary.

But if the HST relies on hydraulic oil that is only filtered by a single typical screw-on hydraulic filter (often a 30 micron) - then I WOULD drain the HST when doing a system fluid change.

The nice thing about the systems that have the two screw on filters - the 30 and the 10 micron - is that eventually all of the trans/hydraulic oil passes through the finer filter. In that way the HST charge pump and fine filter act like a "bypass" or "polishing" filter for the entire trans/hydraulic system. That's a nice bonus..

rScotty

Hmm, I'm really hijacking this thread now. : (

“Fergie” has only one hydraulic oil pump (positive displacement, and open center system); there is no separate HST charge pump. There is a screen/strainer in the transmission housing where the oil is drawn from, and another small screen/strainer between the pump and the "control valve". The pump's output goes to a divider valve inside the "control valve" with one side going to the steering valve and the other to the loader valve and beyond. The “power beyond” from the steering gear goes to a tee with the PTO clutch on one side and the PTO relief valve on the other. When the PTO relief valve pops open (which is apparently 99%+ of the time) it "drains" through the main hydraulic oil filter (only a single real filter) to the hydrostatic transmission and back to the tank, which in this case is the main transmission housing. I.e., the filter output is the pseudo "charge pump" to the HST.