L5740HST Drivetrain Slipping

garf658 · Oct 15, 2017

I was finishing up some rotary cutting for the day when I noticed a chattering noise while turning corners. Front wheels were not falling off so I decided to drive the tractor home immediately, and by the time I made it back 2 miles the drivetrain was slipping so badly I could only move in Mid range, low speed at 4 mph. When I tried high speed, it created a terrible grinding noise equivalent to shifting a vehicle without clutching. Made no difference in 2 or 4wd.
The clutch still works fine to engage the pto, so that seems ok. Once I reached the yard it seemed to work slightly better in reverse, probably because that side of the gears has not been chewed off yet.
It almost seems like a spline shaft has backed out, and is just barely making contact with the driven gear.
Tractor has 298 hrs, I envision thousand dollar bills floating away to the dealer next week. Any thoughts?

whirly · Oct 15, 2017

Have you checked the HST oil level recently?

diesel85 · Oct 15, 2017

As whirly said, I recommend checking your fluid levels.

But it sounds like you have other issues going on. I would pull the filter to see if there is any chunks of metal debris. If you see that, then you need to have it serviced.

rbargeron · Oct 17, 2017

First step is to make sure trans oil level is good. But if fluid is way low, the HST just quietly stops sending power to the wheels. The HST uses the same internal parts for F and R, so if one direction is really different the grinding noise is not likely related to the HST.

The racket could be from broken shifter parts in the range gearbox, or possibly a failibg/failed main clutch. The foot clutch disk at the engine flywheel powers everything else from there back. (The small hydraulic pto clutch only affects whether the pto is engaged)

To isolate symptoms, jack up both rear wheels, select 2wd, select high range, idle the engine and see what it sounds like. If reasonably quiet, slowly push HST pedal toward F, back to N, and toward R, noting how it acts with low turning resistance in the drivetrain. If there's less noise than when driving, it would point to the range gear selector parts. May still mean splitting the machine but unlikely to be crazy expensive. Good luck, and let us know what is found. Dick B

SPYDERLK · Oct 17, 2017

garf658 said:
I was finishing up some rotary cutting for the day when I noticed a chattering noise while turning corners. Front wheels were not falling off so I decided to drive the tractor home immediately, and by the time I made it back 2 miles the drivetrain was slipping so badly I could only move in Mid range, low speed at 4 mph. When I tried high speed, it created a terrible grinding noise equivalent to shifting a vehicle without clutching. Made no difference in 2 or 4wd.
The clutch still works fine to engage the pto, so that seems ok. Once I reached the yard it seemed to work slightly better in reverse, probably because that side of the gears has not been chewed off yet.
It almost seems like a spline shaft has backed out, and is just barely making contact with the driven gear.
Tractor has 298 hrs, I envision thousand dollar bills floating away to the dealer next week. Any thoughts?

Sounds like some failure in the differential. Is the problem really range related -- What happens if you engage diff lock?

garf658 · Oct 18, 2017

Its loaded on the trailer and going into the dealer tomorrow.
After looking at the online parts diagrams, I could see a coupling failure occurring between the spline shafts of the hst and transmission. As to checks; oil level is good, diff lock works. I can hold the unit in place with the brakes, and put the hydro pedal down to hear the gears grinding. If I release the brakes it goes forward and shifts between high or low speed. Reverse works way better, due to the gears not being chewed off as much. That's how it went onto the trailer. I'll keep you guys posted.

garf658 · Nov 16, 2017

So the techs finally lifted the cab and split the tractor to discover this mess in the hydro drive. I see what parts were making the grinding noise now. One of the pistons in the hydro motor broke loose and helped chew up the others with the brass filings.
First parts estimate (plus the 30 hrs shop time @ $130) was $8k for a complete new hydrostatic. Once they disassembled, they revised it to $1700 for the parallel motors and $1700 for a new pump. Techs stated they rarely have ever seen a hydro failure, but for me with just under 300 hrs use I'm sure not impressed having to deal with it.
I guess its a lesson for me anyways, that if I cannot come close to using the warranty hours on a machine I sure will never consider buying a new one to include it.

Fallon · Nov 16, 2017

Ouch. I've rarely heard of HST issues myself here on TBN or elsewhere & thats what my dealer has told me as well.

rbargeron · Nov 16, 2017

After reading your first post of the symptoms, I tried to offer some tests to narrow the possibilities. Carnage like this in an HST's pump/motor is really rare. Different noises in forward and reverse is very odd too because all the same parts are working, just turning the other way.

Perhaps your dealer can arrange to get Kubota factory help examining (and correcting) this bizarre failure of a young machine. It's not supposed to happen. TBN posts about HST issues are almost always traceable to linkage on the outside. I was hoping yours wasn't as serious a problem as it clearly is. Sorry my post was too optimistic. Dick B.

Greenfield Dave · Nov 16, 2017

garf658 said:
So the techs finally lifted the cab and split the tractor to discover this mess in the hydro drive. I see what parts were making the grinding noise now. One of the pistons in the hydro motor broke loose and helped chew up the others with the brass filings.
First parts estimate (plus the 30 hrs shop time @ $130) was $8k for a complete new hydrostatic. Once they disassembled, they revised it to $1700 for the parallel motors and $1700 for a new pump. Techs stated they rarely have ever seen a hydro failure, but for me with just under 300 hrs use I'm sure not impressed having to deal with it.
I guess its a lesson for me anyways, that if I cannot come close to using the warranty hours on a machine I sure will never consider buying a new one to include it.

View attachment 528631 View attachment 528630

Ouch!!
Why isn't it under warranty? I thought 300 hours was the cutoff...

ProjectKing · Nov 16, 2017

garf658 said:
So the techs finally lifted the cab and split the tractor to discover this mess in the hydro drive. I see what parts were making the grinding noise now. One of the pistons in the hydro motor broke loose and helped chew up the others with the brass filings.
First parts estimate (plus the 30 hrs shop time @ $130) was $8k for a complete new hydrostatic. Once they disassembled, they revised it to $1700 for the parallel motors and $1700 for a new pump. Techs stated they rarely have ever seen a hydro failure, but for me with just under 300 hrs use I'm sure not impressed having to deal with it.
I guess its a lesson for me anyways, that if I cannot come close to using the warranty hours on a machine I sure will never consider buying a new one to include it.

View attachment 528631 View attachment 528630

Completely unacceptable! Especially at 300 hours. Clearly pump had a defect when it was made leading to failure. I would raise h$ll over this with Kubota.

garf658 · Nov 16, 2017

I think it is a 2008 machine. Don't remember the warranty details from back then.

MHarryE · Nov 16, 2017

I have a few bags of similar hydro piston around as souvenirs all resulting from low oil viscosity. Our problem was having released for production a machine that did not meet our hydraulic cooling requirement and in Middle East heat, oil viscosity became so low piston slippers started melting down. It was surprising how long the machines would run before one piston slipper would completely fail and the machine would stop.

garf658 · Nov 16, 2017

Thks for the info. I don't have my record book now to know exactly when I did the first hydraulic change, but It was replaced with the super UDT and a factory filter. This summer I used my 8 ft disc in high 80 heat for an afternoon, while the failure occurred in 60 degree temps in Oct.

ProjectKing · Nov 17, 2017

garf658 said:
Thks for the info. I don't have my record book now to know exactly when I did the first hydraulic change, but It was replaced with the super UDT and a factory filter. This summer I used my 8 ft disc in high 80 heat for an afternoon, while the failure occurred in 60 degree temps in Oct.

Heck even if you did no maintenance... it shouldn’t fail at only 300 hours!

rbargeron · Nov 17, 2017

Any chance of pictures of more parts? The most deformed slipper looks like something else was chewing on it as it went around. If it was an overheating situation seems like there would be some scorching or discoloration? The charge pump body (in the background) still looks decent. Failed Kubota (Kayaba?) hydrostats are rare to see in the flesh. You must want to get it running again asap - but it would be great to preserve the evidence of the wreckage for forensic study.

dfkrug · Nov 17, 2017

rbargeron said:
If it was an overheating situation seems like there would be some scorching
or discoloration?

It looks like the slippers have worn down quite a bit. Pix of the valve plates would be nice to see as well.

Overheating the fluid can sure destroy an HST, but that one exploded slipper sure points toward a defect.

(Thx for posting pix, GARF.)

crazyal · Nov 17, 2017

It may have just been a defective part. It happens. I would think if it was bad oil then all of them would look similar. I guess it's possible something floating around in the oil got stuck on the face and damaged it. I doubt you'll get much help if it's a 2008 even though the hours are low.

lakeridge · Nov 19, 2017

There is a known manufacturing issue with a serial number range of L40 HST transmissions. The tolerance between the HST piston and bores are to tight and will seize in the bore. The slipper will get hammered against the swashplate when it gets tight in the bore and either pull the slipper completely off the piston or hammer the face as has happened to yours. I had this failure occur when my tractor was within the warranty period. Make sure your dealer installs the most current parts or this could happen again. I would ask your dealer to contact kubota if they are not aware of this type of failure and proper repair solution. No problems with my HST since new parts were installed.

ProjectKing · Nov 19, 2017

lakeridge said:
There is a known manufacturing issue with a serial number range of L40 HST transmissions. The tolerance between the HST piston and bores are to tight and will seize in the bore. The slipper will get hammered against the swashplate when it gets tight in the bore and either pull the slipper completely off the piston or hammer the face as has happened to yours. I had this failure occur when my tractor was within the warranty period. Make sure your dealer installs the most current parts or this could happen again. I would ask your dealer to contact kubota if they are not aware of this type of failure and proper repair solution. No problems with my HST since new parts were installed.

Great information!! I hope OP reads this.