L3750 lost hydraulics after filter change

[stvdilln]

The tractor was bought at an auction a couple of months ago. It looks like somebody was working on a restoration, new paint and decals. It has about 6000 hours. No history avail. We bought it to pull a row bed maker that is too big for our other tractor.
Last week we tested and the hydraulics were slow and we had to rev it to get it to lift the 600 lb implement.
Adding another 200 lbs of drip tape and plastic mulch the tractor refused to lift it.
The dash had a warning light for hydraulic filter blocked so we replaced that. Filter only, lost about 2 qts of fluid.
after filter change, the 3pt won’t lift even with no attachment and the hydro shuttle won’t shift.
Is there some priming or trick needed For what we did?

 

[jyoutz]

The tractor was bought at an auction a couple of months ago. It looks like somebody was working on a restoration, new paint and decals. It has about 6000 hours. No history avail. We bought it to pull a row bed maker that is too big for our other tractor.
Last week we tested and the hydraulics were slow and we had to rev it to get it to lift the 600 lb implement.
Adding another 200 lbs of drip tape and plastic mulch the tractor refused to lift it.
The dash had a warning light for hydraulic filter blocked so we replaced that. Filter only, lost about 2 qts of fluid.
after filter change, the 3pt won’t lift even with no attachment and the hydro shuttle won’t shift.
Is there some priming or trick needed For what we did?

Did you top off the fluid?

 

[stvdilln]

Did you top off the fluid?

I topped off with what I had in shop, but it is just a bit low still like a 1/8 of inch from full mark, we ran to tractor supply last night and bought more, will be adding that this morning.

 

[TheOldHokie]

The tractor was bought at an auction a couple of months ago. It looks like somebody was working on a restoration, new paint and decals. It has about 6000 hours. No history avail. We bought it to pull a row bed maker that is too big for our other tractor.
Last week we tested and the hydraulics were slow and we had to rev it to get it to lift the 600 lb implement.
Adding another 200 lbs of drip tape and plastic mulch the tractor refused to lift it.
The dash had a warning light for hydraulic filter blocked so we replaced that. Filter only, lost about 2 qts of fluid.
after filter change, the 3pt won’t lift even with no attachment and the hydro shuttle won’t shift.
Is there some priming or trick needed For what we did?

• The dash warning light probably indicated an overly high suction pressure in the oil supply line.
• You now have no hydraulic pressure probably becuase the pump is not picking up its oil supply.
• Is the warning light out now?

Dan

 

[stvdilln]

The warning light now occasionally flickers with revs, but is on at idle. I didn't change the fluid as it looked ok to my untrained eye. Is next step just to change the fluid as well and hope to flush out blockage, or is there a procedure/manual on cleaning hydraulic pump.
I am an intermediate car mechanic, with a decent collection of tools, but new to tractors. Tell me where to find a manual to follow and what I should do and I'm on it.
Steve

 

[TheOldHokie]

The warning light now occasionally flickers with revs, but is on at idle. I didn't change the fluid as it looked ok to my untrained eye. Is next step just to change the fluid as well and hope to flush out blockage, or is there a procedure/manual on cleaning hydraulic pump.
I am an intermediate car mechanic, with a decent collection of tools, but new to tractors. Tell me where to find a manual to follow and what I should do and I'm on it.
Steve

I prefer to do some diagnostics before launching into any major disasembly.

You trouble shoot hydraulic circuits much like electrical circuits. First identify the wiring/plumbing and then start testing as you move along the circuit. You had poor function before you changed the filter and now you have none. That suggests a flow//supply problem at the pump. So the first thing I would do is check for output flow from the pump. You can do that quickly and easily at the point indicated in this parts diagram. Disconnect the pump supply line at fitting number 180 and slip a length of cheap clear vinyl tub over the end of the pipe. A small hose clamp is good insurance againd it blowing off and making an oily mess. Put the pther end of the tube in the hydraulic filler hole and secure it in the hole for the same reason. Now start the tractor and observe the flow coming from the pump. If you have a good solid flow we move on to a pressure test. If poor flow we start working on the suction side of the pump. This should be easy and fast to nail down.

Dan

 

[Russell King]

@TheOldHokie said “pump supply line at fitting” but I believe he meant “pump output line at fitting” above

 

[TheOldHokie]

@TheOldHokie said “pump supply line at fitting” but I believe he meant “pump output line at fitting” above

Oh the joys of the English language. I try to make a point of avoiding ambiquous references but I don't always succeed.

Its the oil line coming from the pump that supplies pressurized oil to the tractor as shown/described in the accompanying parts diagram and identified wiith reference number 180.

Dan

 

[stvdilln]

The warning light now occasionally flickers with revs, but is on at idle. I didn't change the fluid as it looked ok to my untrained eye. Is next step just to change the fluid as well and hope to flush out blockage, or is there a procedure/manual on cleaning hydraulic pump.
I am an intermediate car mechanic, with a decent collection of tools, but new to tractors. Tell me where to find a manual to follow and what I should do and I'm on it.
Steve

Sorry for the delay, I’m in south Florida and had to deal with our 2nd possible hurricane this fall.
Opening the hydraulics at the connector just before the splitter yielded a gusher of a flow. After that test, hydraulics improved back to original poor performance. The hydraulic shift now works, 3 point works with mo attachment but can’t lift the 700 lbs or so bed making implement.
We noticed rusted metal bits in the hydraulic fluid in the drain pan from our filter change, so we changed hydraulic fluid, but that didn’t make a change in performance.
Is next step a pressure test at same point?

 

[TheOldHokie]

Sorry for the delay, I’m in south Florida and had to deal with our 2nd possible hurricane this fall.
Opening the hydraulics at the connector just before the splitter yielded a gusher of a flow. After that test, hydraulics improved back to original poor performance. The hydraulic shift now works, 3 point works with mo attachment but can’t lift the 700 lbs or so bed making implement.
We noticed rusted metal bits in the hydraulic fluid in the drain pan from our filter change, so we changed hydraulic fluid, but that didn’t make a change in performance.
Is next step a pressure test at same point?

Probably not at that point. We need to know where the main pressure relief is and test immediately down stream of it. We went down this rabbit hole in a previous thread - I will have to go back and see where that was finally located.

Dan

 

[Oil pan 4]

I had a weapons load truck lose hydraulics after a filter change a few times. The filter is on the suction side of the pump for these things.
One time a guy changed the filter and put 2 o-rings, the old one stuck to the head plus the new one, that caused a slight air leak, took me longer than it should have to find it.
Then a filter got put on with a cut o-ring,
The last time it happened a guy didn't put the o-ring on at all.
I know the manufacturers like those suction side filters, they are like 1/4 to 1/10 the cost of a high pressure filter.

 

[TheOldHokie]

Sorry for the delay, I’m in south Florida and had to deal with our 2nd possible hurricane this fall.
Opening the hydraulics at the connector just before the splitter yielded a gusher of a flow. After that test, hydraulics improved back to original poor performance. The hydraulic shift now works, 3 point works with mo attachment but can’t lift the 700 lbs or so bed making implement.
We noticed rusted metal bits in the hydraulic fluid in the drain pan from our filter change, so we changed hydraulic fluid, but that didn’t make a change in performance.
Is next step a pressure test at same point?

OK - had to go refresh my memeory. On the L4150 the releif is in the hydraulic outlet. I would doble check that before proceeding - there should be a hex head plug on teh front back side of the block.

If so it looks it like the easiest place to pressure test is at the end of the 3pt supply line.

Dan

 

[stvdilln]

I had a weapons load truck lose hydraulics after a filter change a few times. The filter is on the suction side of the pump for these things.
One time a guy changed the filter and put 2 o-rings, the old one stuck to the head plus the new one, that caused a slight air leak, took me longer than it should have to find it.
Then a filter got put on with a cut o-ring,
The last time it happened a guy didn't put the o-ring on at all.
I know the manufacturers like those suction side filters, they are like 1/4 to 1/10 the cost of a high pressure filter.

Thanks since it wasn’t working very well before the filter, it has now returned to its initial state before the filter change. Which is a very low lift capacity on 3pt hitch.

 

[stvdilln]

OK - had to go refresh my memeory. On the L4150 the releif is in the hydraulic outlet. I would doble check that before proceeding - there should be a hex head plug on teh front back side of the block.

If so it looks it like the easiest place to pressure test is at the end of the 3pt supply line.

Dan

View attachment 90477

I’ll have to track down an appropriate gauge, and will test just before the cylinder.

 

[TheOldHokie]

I’ll have to track down an appropriate gauge, and will test just before the cylinder. View attachment 90483

My crystal ball is far from infallible but its telling me that your pressure test is most likely going to indicate low oil pressure. So then the question becomes why and what component is causing it.

At that point you will need to start working back towards the pump and pressure testing on the pump side of the outllt block will require a more sophisticated apparatus. You might want to keep that in mind when purchasing a gauge and fittings. Since you will be testing on the pump side of the outlet block there is no pressure releif in the system and you will need a setup to allow you to control pressure so you don't deadhead the pump. The setup shown below is a little flow control valve and gauge manifolded together with a tee and makes a simple and inexpensive test rig.

To conduct a test:

1. Hook the hose end to the pump side of the hydraulic circuit and run a piece of (clear??) low pressure tubing from the barb back to the sump filler.
2. Fully open the flow control valve and start the tractor. DO NOT EVER FULLY CLOSE THE VALVE WITH THE TRACTOR ENGINE RUNNING
3. Now gradually start to close the flow control valve and watch pressure build.

You should get to full operating oil pressure (~2000 PSI) with the valve partially open. If you can't either the pump is bad or something between the test point and the pump is bleeding off pressure. Move the test point closer to the pump and try again. If you get all the way back to the pump and still no pressure the pump is bad,

Dan

 

[stvdilln]

My crystal ball is far from infallible but its telling me that your pressure test is most likely going to indicate low oil pressure. So then the question becomes why and what component is causing it.

At that point you will need to start working back towards the pump and pressure testing on the pump side of the outllt block will require a more sophisticated apparatus. You might want to keep that in mind when purchasing a gauge and fittings. Since you will be testing on the pump side of the outlet block there is no pressure releif in the system and you will need a setup to allow you to control pressure so you don't deadhead the pump. The setup shown below is a little flow control valve and gauge manifolded together with a tee and makes a simple and inexpensive test rig.

To conduct a test:

1. Hook the hose end to the pump side of the hydraulic circuit and run a piece of (clear??) low pressure tubing from the barb back to the sump filler.
2. Fully open the flow control valve and start the tractor. DO NOT EVER FULLY CLOSE THE VALVE WITH THE TRACTOR ENGINE RUNNING
3. Now gradually start to close the flow control valve and watch pressure build.

You should get to full operating oil pressure (~2000 PSI) with the valve partially open. If you can't either the pump is bad or something between the test point and the pump is bleeding off pressure. Move the test point closer to the pump and try again. If you get all the way back to the pump and still no pressure the pump is bad,

Dan

View attachment 90499

Thank you so much for all the great help and time and hopefully a thread that others will find in the future. Will build out this test rig and will follow up in several days with the results.

 

[TheOldHokie]

Thank you so much for all the great help and time and hopefully a thread that others will find in the future. Will build out this test rig and will follow up in several days with the results.

You are more than welcome. I did not invent that procedure. You will find that same test setup and procedure in the Kubota work shop manuals.

Dan