Broken HST/ No Reverse= HUGE $ to Fix!

[dfkrug]

I remember some hydraulic shuttles on older models that could change direction
quick enough for a face plant in the steering wheel.

Until I drove a new L5740 a few years ago, I thought that was a feature, not a bug. My older HSTs have all
been pretty abrupt. I guess some of that is due to age and damper wear, but some seems designed-in (Deeres).
All my Kiotis have been very smooth and damped.

 

[rbargeron]

......They orifice the flow to the servo piston so the swash plate doesn't tilt too fast.....Each side of the piston is orificed separately......if it gets a chunk in it, it may not stroke at all or it may become erratic...The fix.. is to pull the orifice and clean it .....

Good suggestion Michael - the servo piston has a removable bottom head. I took it off and drained it (oil was dark but no metal chips). I blew out the feed passage from the regulator - it has an orifice pressed into one end - seemed clear. The piston is vertical and goes up for reverse, so I was glad to be able to clean it. Getting at the top of the piston and its feed passage requires taking more floor & cowl parts off. I'll do that and have a look to make sure there's nothing visible preventing the piston from moving up. It's still keyed into the swashplate so it won't want to move very far. But maybe I can verify smooth travel short of separating the tractor.

 

[rbargeron]

Update - the piston can move in both directions ok. Pilot hydraulic pressure moves it down (for forward) normally. But for upward motion (reverse) only a tiny amount of pilot pressure is getting to it.

Stopped on level ground it barely moves backward - but I noticed that starting down an incline in reverse, the tractor will then build speed and act normal. It's obvious the piston and swashplate are moving ok then. Once the tractor is moving backward there's plenty of power to keep going. The grade can level out or go up but the tractor maintains normal torque and speed - in reverse. Pretty sure the regulator still has an issue. I haven't found it yet but I'm closing in on it. If you have read this far, my thanks for your patience. Describing it to someone else helps me understand it myself.

 

[rbargeron]

Here are a few pictures of the process so far. I didn't find images on the net for the HST regulator so I figured I'd post some. This L48 is the later style so the parts book says it shares HST design with Grand L3010 thru L4610 machines. Taking it off required a little patience but compared to splitting the tractor it was duck soup. It's a bit odd working on this heavy machine with jeweler's tools.

 

[brain55]

Very nice

 

[curtisfarmer]

Hi Dick,

Looks like you are making progress! Good for you! I sent you a PM a while back about your email so I can send the diagnostic results (pretty bare description from dealer) and your address to send the linkage arm. I'll look for your reply. Best regards, Matt

 

[rbargeron]

The L48 again has reverse !! All that noise inside the regulator was due to the "neutral" adjustment being off.

I had earlier found the regulator valve didn't move freely but after freeing it up and reinstalling it the behavior was still the same. So then I tested the regulator on the bench with air instead of oil from the charge pump - with the valve "centered" the two outlet ports (pic above) should have been blocked. But the forward port was getting air in neutral. That would mean that moving toward reverse both sides of the piston were getting pressure and it didn't move. Anyway I adjusted the stop to put the valve in the middle of the sweet spot (no flow in neutral). With the regulator back on the tractor, the HST pedal put it in reverse right away.

The thing I noticed is how narrow the regulator's sweet spot is. Pretty tricky to get it just right so both ports are blocked in the center. This is good in a way because when it's right it makes a very responsive linkage. But it also turned on another light bulb.

The picture below is looking up from under the tractor. The bottom of the regulator sticks down and gets rubbed by grass and weeds, sticks etc. - notice the gray paint is worn thru to the white primer. When I first took the regulator off I noticed the end of the adjusting screw was slightly damaged (deformed enough that an Allen wrench wouldn't go in) I used a die grinder on the bad spot and didn't think about it much. But the bottom of the regulator housing is aluminum and anything that could whack the steel adjusting screw hard enough to deform it might cause just enough permanent deformation of the aluminum to upset the regulator's sweet spot. We're talking half a millimeter or less, so it's plausible. Couldn't tell for sure whether the locknut had been loosened or if it had ever been adjusted before. But regardless it works now.

Part cost: 1 regulator gasket $10
Tool cost: 1- T25 torx bit (cut short) $7
Materials: about 1 qt SUDT not recovered - $10
Labor cost: would have watched the Mecum Auction anyway
Not paying Kubota's confiscatory HST part prices: quietly satisfying

Dick B

 

[CanuckPT]

Way to go Dick!!! Problem solved - inexpensively! Sense of accomplishment - priceless!!!

 

[crazyal]

Just think of all the knowledge you've gained. I would like to think that a dealer should have been able to figure this out but maybe it's an extremely rare fail so they've never heard of it.

 

[k0ua]

The L48 again has reverse !! All that noise inside the regulator was due to the "neutral" adjustment being off.

I had earlier found the regulator valve didn't move freely but after freeing it up and reinstalling it the behavior was still the same. So then I tested the regulator on the bench with air instead of oil from the charge pump - with the valve "centered" the two outlet ports (pic above) should have been blocked. But the forward port was getting air in neutral. That would mean that moving toward reverse both sides of the piston were getting pressure and it didn't move. Anyway I adjusted the stop to put the valve in the middle of the sweet spot (no flow in neutral). With the regulator back on the tractor, the HST pedal put it in reverse right away.

The thing I noticed is how narrow the regulator's sweet spot is. Pretty tricky to get it just right so both ports are blocked in the center. This is good in a way because when it's right it makes a very responsive linkage. But it also turned on another light bulb.

The picture below is looking up from under the tractor. The bottom of the regulator sticks down and gets rubbed by grass and weeds, sticks etc. - notice the gray paint is worn thru to the white primer. When I first took the regulator off I noticed the end of the adjusting screw was slightly damaged (deformed enough that an Allen wrench wouldn't go in) I used a die grinder on the bad spot and didn't think about it much. But the bottom of the regulator housing is aluminum and anything that could whack the steel adjusting screw hard enough to deform it might cause just enough permanent deformation of the aluminum to upset the regulator's sweet spot. We're talking half a millimeter or less, so it's plausible. Couldn't tell for sure whether the locknut had been loosened or if it had ever been adjusted before. But regardless it works now.

Part cost: 1 regulator gasket $10
Tool cost: 1- T25 torx bit (cut short) $7
Materials: about 1 qt SUDT not recovered - $10
Labor cost: would have watched the Mekum Muscle Car Auction anyway
Not paying Kubota's confiscatory HST part prices: quietly satisfying

Dick B

Wow!.. way to go, you da' man.:thumbsup: If I ever have hydro trouble, I know who I want working on mine!

James K0UA