M4900 Hydraulic Problems. Power steering, PTO are OK. Everything else weak

[wheelinag]

My intelligent colleague just made a good point. Maybe there is some kind of suction problem? How much PSI does it take to make the steering work?

 

[TheOldHokie]

My intelligent colleague just made a good point. Maybe there is some kind of suction problem? How much PSI does it take to make the steering work?

I dont see this being a suction side problem and I don't like guess work when I can quantify things.

You now have a pump pressure test adapter - test the PS pump. PS pressure relief specification is 2631 PSI. Also measure the flow rate coming to the loader valve. All that takes is a bucket and a stop watch.

Dan

 

[wheelinag]

I dont see this being a suction side problem and I don't like guess work when I can quantify things.

You now have a pump pressure test adapter - test the PS pump. PS pressure relief specification is 2631 PSI. Also measure the flow rate coming to the loader valve. All that takes is a bucket and a stop watch.

Dan

I'll do this when I get the pump in as I'll be taking that off anyways.

While I haven't done any flow tests yet, I've discharged fluid into a bucket quickly a couple of times and did the pressure tests into a bucket as well. Probably 20 seconds total, but I'd say there's a little over a few gallons in there. Obviously not very scientific.

I need to put it on the back burner until the pump gets in and catch up on work.

 

[Russell King]

Just to provide you with more information on the tank return line since you asked a question that I didn’t see an answer to.

These Kubota tractors have open center hydraulic systems (for the most part). That means each valve just lets the hydraulic oil flow through with little pressure since there is no restriction to flow. The Power In port is the feed into the valve, a Power Beyond sleeve is added to one port that allows the open center flow to the next valve. Most valves in modern hydraulic systems have two lines that go to a double acting valve, pressure on one side forces the piston and ram to move. Tho other hose is used as a return line so the hydraulic fluid is fed back to the valve. Then the valve has a Tank Return port that dumps the fluid back to the tractor sump.

So most valves today on smaller Kubota tractors will have three lines (P, PB, T) connected to them. In older systems the valve may only use 2 lines and that can cause problems with too much pressure in the valve body (if I recall correctly).

 

[TheOldHokie]

Just to provide you with more information on the tank return line since you asked a question that I didn’t see an answer to.

These Kubota tractors have open center hydraulic systems (for the most part). That means each valve just lets the hydraulic oil flow through with little pressure since there is no restriction to flow. The Power In port is the feed into the valve, a Power Beyond sleeve is added to one port that allows the open center flow to the next valve. Most valves in modern hydraulic systems have two lines that go to a double acting valve, pressure on one side forces the piston and ram to move. Tho other hose is used as a return line so the hydraulic fluid is fed back to the valve. Then the valve has a Tank Return port that dumps the fluid back to the tractor sump.

So most valves today on smaller Kubota tractors will have three lines (P, PB, T) connected to them. In older systems the valve may only use 2 lines and that can cause problems with too much pressure in the valve body (if I recall correctly).

His valve has IN, PB, and TANK via the manifold.. Its the unused work port thats the issue.

Dan

 

[wheelinag]

To start off, I didn't check the power steering side pressure. There was no way I was fitting anything in between the pump and the hardline without taking the entire hard line off and I really didn't want to take the dash apart to get to the steering valve. A fairly interesting observation was that that when all the intake and pressure lines were off the pump, the steering side was still fluid all the way to the top, and the main side had no fluid in it.

I had read that somewhere on this forum that someone used a chinese pump, but the bolt's didn't line up correctly. I measured the individual ports on the top and they were fine. Get the pump off and first thing I notice is the new shaft doesn't have a snap ring groove to hold the drive gear on. Secondly, the pump is shorter. Looks like there are spacers in the middle that are different. The shaft wouldn't be an issue, I'd probably just be lazy and grind a groove carefully with a thin cutoff wheel. The spacing is an issue for the bottom, as the the ports on the hardline are fixed.

I'm going to take the main side of the pump apart and see if anything is apparently wrong. I don't think I have much to lose at this point.

 

[wheelinag]

Alright experts, seal kit? Worth a try for $100? I thought there was varnish in there at first, but looks like it's a backer.

The only real concerning thing I can see is the wear on the aluminum bushing holders. Not actually sure what they are called.

Pics.

 

[TheOldHokie]

Alright experts, seal kit? Worth a try for $100? I thought there was varnish in there at first, but looks like it's a backer.

The only real concerning thing I can see is the wear on the aluminum bushing holders. Not actually sure what they are called.

Pics. View attachment 155574 View attachment 155574 View attachment 155575 View attachment 155576 View attachment 155577 View attachment 155578

The pump has self destructed from oil starvation or over pressure. A seal kit is not going to fix it. If the new pump will fit put it on. If not a new OEM pump is $2K.

Dan

 

[wheelinag]

The pump has self destructed from oil starvation or over pressure. A seal kit is not going to fix it. If the new pump will fit put it on. If not a new OEM pump is $2K.

Dan

I could cut the intake tubes and reweld them to fit this pump, or make an adapter plate, but with the shaft also not having the two grooves for the snap rings, I'm worried about what else in the pump is wrong. I'm probably just going to buy an OEM pump.

What I really want to know is why this pump failed at that moment, so the new pump doesn't fail the same way. There was plenty of fluid at the time of failure. All I had done for the previous 6 hours was use the mower and push around a little dirt from irrigation ditches with the loader. There was not lack of power, noise, etc...

The seals were not in good shape. Did the seal cause the failure or did failure chew up the seals?

I will add another line to the cylinder on the mower. Maybe 1000's of times of hitting the relief valve pressure caused this? The last time was just the straw that broke the camels back?

 

[TheOldHokie]

I could cut the intake tubes and reweld them to fit this pump, or make an adapter plate, but with the shaft also not having the two grooves for the snap rings, I'm worried about what else in the pump is wrong. I'm probably just going to buy an OEM pump.

What I really want to know is why this pump failed at that moment, so the new pump doesn't fail the same way. There was plenty of fluid at the time of failure. All I had done for the previous 6 hours was use the mower and push around a little dirt from irrigation ditches with the loader. There was not lack of power, noise, etc...

The seals were not in good shape. Did the seal cause the failure or did failure chew up the seals?

I will add another line to the cylinder on the mower. Maybe 1000's of times of hitting the relief valve pressure caused this? The last time was just the straw that broke the camels back?

The new gear is probably pressed on or retained in some other fashion. I doubt its a manufacturing defect and would not worry me in the least. There are probably other internal differences.

I am assuming the bushing blocks in the old pump are also wear plates. A common design technique is to provide an internal oil passage that uses the oil pressure generated by the pumping gears to push a movable wear plate up against the gears. That compensates for normal wear and limits oil loss (slip) caused by excessive end clearances. From the looks of your failure the wear plates were destroyed by the gears. Two things come to mind - excessive pressure and/or insufficient oil. I dont think the case seals had a role in the failure.

At this point in my life I am inclined to spend money for parts rathrr than retrofit things. But $2K is a lot of money and a little bit of hose is cheap. Welding would not be in my game plan.

Dan

 

[wheelinag]

The gear is probably pressed on or retained in some other fashion. I doubt its a manufacturing defect and would not worry me in the least. There are probably other intermal differences.

I'd still have to cut grooves for snap rings to locate my gear correctly.

Two things come to mind - excessive pressure and/or insufficient oil. I dont think the case seals had a role in the failure.

Ok, but why now when it wasn't really being used hard? Mainly, I just don't want to repeat this.

At this point in my life I am inclined to spend money for parts rathrr than retrofit things. But $2K is a lot of money and a little bit of hose is cheap. Welding would not be in my game plan.

I'm probably just going to go OEM. I need the tractor sooner than later. I work for myself, so time working on this is taking away from that.

Lastly, when I called the hydraulic shop last week, they said they have a guy there who rebuilds these type of pumps. I'm skeptical as I can't find parts. It could definitely end up that the guy on the phone doesn't know this style pump. I guess I'll find out tomorrow and talk with them before I buy and new pump. Anyone had luck with going this route?

 

[TheOldHokie]

I could cut the intake tubes and reweld them to fit this pump, or make an adapter plate, but with the shaft also not having the two grooves for the snap rings, I'm worried about what else in the pump is wrong. I'm probably just going to buy an OEM pump.

What I really want to know is why this pump failed at that moment, so the new pump doesn't fail the same way. There was plenty of fluid at the time of failure. All I had done for the previous 6 hours was use the mower and push around a little dirt from irrigation ditches with the loader. There was not lack of power, noise, etc...

The seals were not in good shape. Did the seal cause the failure or did failure chew up the seals?

I will add another line to the cylinder on the mower. Maybe 1000's of times of hitting the relief valve pressure caused this? The last time was just the straw that broke the camels back?

Probably more than you ever wanted to know about external gear pump design and operation:

https://apps.dtic.mil/sti/trecms/pdf/AD1169714.pdf

There are some things that are just not rebuildable. Small external gear pumps are in that category.

Dan