B7100 HST 4wd swash plate stop bolt

[Henro]

The "diagram" the OP refers to is a drawing posted on TBN (copy posted here below). The HST unit shown is oriented the other way up from the diagrams in the Kubota parts lists - hence all the confusion about upper and lower.

Once we get past that, the "stop bolt" in question locates the motor's thrust plate to keep it from rotating. The plate's angle is fixed - the motor slippers slide on it as the motor block rotates. To keep the thrust plate from rotating, a "stop bolt" engages a notch on the edge.

The stop bolt is important because the sippers need to ride a film of oil constantly to dissipate heat and prevent wear. If the thrust plate is allowed to rotate, the sliding surfaces would become damaged very soon.

Theoretically its possible the "notch" could come back into view, but it's a long shot and risks scratching something.

View attachment 62480

BTW, the actual "swashplate" is part of the PUMP assembly and is not really involved in this.
The pump's swashplate moves - tilting forward and back with the pedal linkage. The MOTOR's corresponding thrust plate is fixed - the angle doesn't change. Its sometimes called a swashplate because the slippers move in and out as their block turns. Kubota just calls it a thrust plate.

I may be a moron, but it sure looks like the OP's image posted at TBN is the same as what whitetiger posted, and that the motor is on the top.

Why do you think the image that the OP posted at TBN shows differently? This inquiring mind wants to know...

 

[rbargeron]

EDIT: This post was deleted when tractor model was corrected to B7100HST. See posts #23 & #27.

 

[Tnkubotaguy]

Okay, I'm a bigger idiot, I posted the correct drawing but I have a B7100D HST 4wd not a B1700 as I wrote on TBN. I must be becoming dyslexic besides getting old, not sure how this will change everyone's opinion but I apologize for all the confusion this is causing, I have the case apart now and seeing if I can move a shaft or something to get than pin hole aligned. No luck yet.

 

[rbargeron]

EDIT: WSM for B7100HST online - see drawing with stop bolt in post #27 below.

 

[Henro]

Well that makes quite a difference - it means your diagram is the right layout (motor on bottom, swashplate/pump on top - my WSM's for the 5 HST Types don't cover the H6640-10600. Sorry but I nuttin' on that one. Hope you can fix it. Good luck - Dick B

Man am I confused now!

Just for my understanding, in the drawings there is a angled piece that I assumed is the swash plate that can be changed in angle, to cause the pump output to the motor to change or reverse. So I assumed that unit was the pump part of the assembly. And the other part was the motor.

Should I be seeing something differently? This is an honest question..I certainly do not know the answer...

 

[rbargeron]

The parts shown at an angle are the MOTOR's "fixed swashplate" and its thrust plate. They stay at that angle.

The HST works basically like this: On this unit (pump above motor) the upper shaft from the engine passes through the variable swashplate (curved on one side, mirror-flat on the slipper side) with a hole in it so it surrounds the shaft, not touching it. The swashplate rides in cradle bearings and can pivot. When it's in neutral (perpendicular to the shaft), the pistons and slippers in the pump body just go round and round and pump flow is zero (motor does not turn).

But when the swash plate tilts. the pistons start sending more oil out on one side. The more it tilts, the greater the flow. The motor always moves in lock-step with the pump output. If the swashplate tilts the other way, past neutral, the motor and output shaft then turn backward, making an infinitely variable reversing coupling between engine and range gearbox.

The passages between the pump chambers and matching motor are connected to each other through slotted valve plates at the ends of the two rotating piston barrels. The clearances are very small and the pumping circuits can reach pressures of several ksi. An HST unit is a near-zero-leakage, variable speed, reversing hydraulic coupling. To make up the small internal leakage between components, a "charge pump" keeps the circuit filled at around 100 psi.

Pretty cool design - to manufacture them you need a zillion-dollar clean-room factory and machine shop to hold the microscopic clearances. That's why the HST assembly is priced high (plus installation) and they can't reasonably be repaired if worn. Luckily if the oil and filter are kept clean and changed on schedule, they last a long time. Dick B.

 

[rbargeron]

Here's the diagram for the B7100HST Type I transmission showing the stop bolt on the bottom.

 

[Henro]

The part that is at an angle is the motor's thrust plate and the fixed swashplate. It stays at that angle (machined to hold it there permanently).

Here's how it works. On this unit (pump above motor) the upper shaft from the engine passes through the swash plate (mirror-flat on the slipper side) with a hole in it so it surrounds the shaft, not touching it. It can pivot (in cradle bearings), but when perpendicular to the shaft, the pistons and slippers in the pump body just spin round and round and pump flow is zero.

When the swash plate tilts. the pistons start sending more oil out on one side. The more it tilts, the greater the flow. The motor always moves in lock-step with the pump. If the swashplate tilts the other way, past neutral, the motor and output shaft turn backward, making an infinitely variable reversing coupling.

The passages between the pump chambers and matching motor are connected to each other through slotted valve plates at the ends of the two rotating piston barrels. The clearances are very small and the pumping circuits can reach pressures over 5000 psi. An HST unit is a near-zero-leakage, variable speed, reversing hydraulic coupling. To make up the small internal leakage between components, a "charge pump" keeps the circuit filled at around 400 psi.

Pretty cool huh? All you need to manufacture them is a zillion-dollar clean-room factory and machine shop to hold the microscopic clearances. That's why the HST assembly is priced high (plus installation) and they can't reasonably be repaired if worn. Luckily if the oil and filter are kept clean and changed on schedule, they last a long time. Dick B.

Thank you for taking the time to write that explanation! Highly appreciated and will be helpful to others now and in the future I am certain.

 

[Henro]

here's the B7100HST trans diagram showing the stop bolt on the bottom View attachment 62514

One thing that confuses me is that the parts diagram that Whitetiger posted the PDF of shows the pump being on the bottom, while the image posted in the reply I am replying to shows the pump being on the top.

Now the parts list posted by WT says it is for a B1700HSD, while the image in the post I am replying to says that image is for a B1700HST. Both cannot be right, unless there is a difference between HSD and HST.

I believe I remember the OP saying his tractor was a HSD...

Edit: after reading the following posts, I see I can't read very well...I transposed the numbers and changed the B7100HST into B1700HST in my mind...insert red face here...

 

[rbargeron]

The important development in this thread is that the base tractor model has been CHANGED from B1700 to B7100, which takes all those earlier-posted parts list pages off the table. See OP's post #22 above.

Whitetiger did post a valid parts diagram - but for what turned out to be a different tractor

In a side conversation with Tnkubotaguy I've sent a link to the WSM for his B7100HST , (where the above Kubota diagram came from).

He says he has the machine apart now and plans to paint it too, while waiting for gaskets, etc. Hope he posts back after a few days with good news.

 

[whitetiger]

One thing that confuses me is that the parts diagram that Whitetiger posted the PDF of shows the pump being on the bottom, while the image posted in the reply I am replying to shows the pump being on the top.

Now the parts list posted by WT says it is for a B1700HSD, while the image in the post I am replying to says that image is for a B1700HST. Both cannot be right, unless there is a difference between HSD and HST.

I believe I remember the OP saying his tractor was a HSD...

The parts pic that I posted was for a B1700 tractor since the title of the thread and OP's information both listed his tractor as a B1700.
Now, magically his tractor has changed from a B1700 to a B7100 which is a completely different hydrostat. Some Kubota hydros have the pump on the bottom, some have the pump on the top, some have the pump and motor side to side. The design depends on the amount of room available and whether the input for the hydro will go to the upper or lower shaft.

 

[Henro]

The parts pic that I posted was for a B1700 tractor since the title of the thread and OP's information both listed his tractor as a B1700.
Now, magically his tractor has changed from a B1700 to a B7100 which is a completely different hydrostat. Some Kubota hydros have the pump on the bottom, some have the pump on the top, some have the pump and motor side to side. The design depends on the amount of room available and whether the input for the hydro will go to the upper or lower shaft.

Yes it did become confusing.

Hopefully the OP will report back with a successful resolution!

 

[number two]

Reminds me of a sign at a parts store-the wrong information will get you the wrong part every time!
Kudos to all that helps that helps this guy out!

 

[Russell King]

What I don’t understand is why that bolt can be easily removed. Why not put some lockplate or cover to indicate that you should not remove it.

I guess that you should just be certain that you are removing the correct bolt but I know on my tractor the drain plugs and other bolts all look the same so I painted the drains red (like they may have been from the factory?)

 

[rbargeron]

I agree that bolt head on the B7100HST with the Type I hst invites loosening!

TheWSM shows a couple versions of that HST. There's a Type I with the lock bolt and a Type II without the lock bolt. I'll bet the OP isn't the first to take it out - and won't be the last !

The Type II version in fact has its DRAIN BOLT on the bottom near the same location ! Not a very friendly setup for potential DIY fluid changers !! Bet it's even caused problems at dealers' shops.

Compare this to the Type I drawing in Post #27 above

 

[rbargeron]

See new inserted WSM image in post #35 above. Before criticizing the OP too much for loosening the wrong bolt, consider the two product versions. I think anybody could fall into a trap like that. My 2 cents. Dick B.

 

[RCW]

See new inserted WSM image in post #35 above. Before criticizing the OP too much for loosening the wrong bolt, consider the two product versions. I think anybody could fall into a trap like that. My 2 cents. Dick B.

Good point, Dick.

It's an unfortunate error, and Lord Only Knows how many I've done in my lifetime.

For those that have never made a mistake, throw the first stone....

Can't/won't sound holier than thou...'cause each time I f-up I swear like a drunken sailor...

Oh wait, I swear a lot anyway.....

I certainly hope the OP can find a good resolution.

 

[rbargeron]

Good point, Dick.

...........I certainly hope the OP can find a good resolution.

I expect he will - when he gets to it.

I knew my L48's HST needed to come apart and I procrastinated for several YEARS before I worked up the courage to actually spread the machine all over my shop!

HST's are not intuitive mechanisms - and they have an "exotic" reputation. But once you first get into one you realize they're just machined parts that fit together really well. Nothing to worry about - except letting dirt get into it. Dick B.

 

[arto98607]

I expect he will - when he gets to it.

I knew my L48's HST needed to come apart and I procrastinated for several YEARS before I worked up the courage to actually spread the machine all over my shop!

HST's are not intuitive mechanisms - and they have an "exotic" reputation. But once you first get into one you realize they're just machined parts that fit together really well. Nothing to worry about - except letting dirt get into it. Dick B.

I appreciate you posting about the L48 HST repair couple years ago and mostly because of that went ahead to open up the HST in my F3060 !
It had sticky HST control pedal & few oil leaks so I wanted to inspect the cradle bearings in order to eliminate chance of those being the problem while I had the mower split already due to oil leaks.

The sticky pedal issue turned out to be external problem but just wanted to make sure and replaced the cradle bearings and all drive train seals 100%

Couple of shaft seals seemed to have shrunken OD and had slightly loose fit in their housing!

It's all back together now and I have put on 10 hours of mowing so far and it is working beautifully.

No more leaks!