L5240 No Forward Only Reverse

[KarlAmherst]

Greetings all,
I am working on a friends L5240.
The problem is that it will only go backwards and not forward.

I started the tractor in Mode "A" test mode and observed T1-T16.

The only thing that did not check out was T12 Swash Plate Position Sensor Voltage.

Pressing the pedal in reverse showed a rise in voltage and the tractor moved backwards.

Pressing the pedal forward did not show an increase in voltage and the tractor did not move forward.
Forward should have displayed between 2.90-4.56(V).
Volts were steady at 2.5.

I pulled the error codes and got
81,82,87,90,91
(81) HST Pedal Sensor Failed
(82) Swash Plate Position Sensor Failed
(87) Tachometer
(90) HST Proportional Valve Forward Failed
(91) HST Proportional Valve Reverse Failed

Troubleshooting, I switched the connectors at Proportional Forward and Reverse Valves.
Pressing the pedal forward resulted in the tractor moving backwards.
Pressing the pedal backwards had no effect.
That lead me to believe the pedal sensor is okay.

I physically switched the proportional valves.
Same effect. Tractor moved backwards when the pedal was moved forward.
I switched the connectors and the tractor moved backwards when the pedal was pressed back.

I'm thinking the pedal sensor is good, the proportional valves are good.
Did I miss something? What should I check out next?

 

[100 td]

My GUESS!
EDIT: One should read your post properly first, before commenting, I missed bits!
What was the lead up to the problem, sequence of events?
Your reverse works correctly, and also works when forwards is selected, but wired to reverse, and you have swapped valves and proven them (the bit I missed).
I guess the position sensor should see some movement and give feedback to the circuit allowing more output. If the correct current isn't flowing into the coil it will also fault, however you have proven the valves. That leaves the position sensor, so either it isn't moving when forward is selected, or it's not seeing the signal for some reason. I don't know what type of sensor, stepper motor perhaps?
Is it possible to remove the position sensor for a look?
Clear all codes and try again and see if you get codes for both valves again, however, only operate the pedal forwards.

 

[KarlAmherst]

A few more details:

Tractor was operating normally then suddenly stopped going forward.

Pedal sensor reads good when testing in Mode A.
Swashplate Sensor does not read good when testing in Mode A.

ERROR 81 - (Pedal Sensor) Should not be able to drive the tractor with the pedal, but should be able to drive it with cruise lever. This is not possible so I don't think this is the error.

ERROR - 82 Swash Plate Position Sensor Failure. Should be able to drive the tractor. This is not possible either, so I don't think this is it.

ERROR - 90 HST Proportional Valve Forward Failure. Should only be able to drive the tractor in reverse. These are the symptoms the tractor is showing.

ERROR - 91 HST Proportional Valve Reverse Failure. Should only be able to drive the tractor forward. This is not possible either, so I don't think this error pertains to this problem.

I'm going to try what you said. Clear the codes and try it again using only forward pedal.

I'm thinking it might be the servo piston not rotating to the forward position.
I'll check the swashplate sensor connection and wiring too.

 

[100 td]

OK, found a manual, -II, is yours a -II?
So pedal ok, both solenoid valves OK, possible blocked oil gallery in F circuit to servo. Is the servo nut on nice and tight.
Can you remove the position sensor and manually operate it while testing? Can you watch the servo indicator shaft rotate with the sensor off?
Possible faulty F relief valve. Do you have gauges, check the F & R relief valves, pull them and swap them over, perhaps a broken spring(I doubt) or a bit of crap?
Be careful, 5300 psi.
The constant voltage in test mode is a sticky point because when you swap the wiring to the reverse it works. Is it because of no feedback?........

 

[KarlAmherst]

Not sure if this one is a II. I'll try to find out.

I'll take out the swash plate position sensor and check its condition. It might be possible to be in test mode and rotate the shaft to see if the voltage increases.

The constant voltage from the sensor might be showing what I'm observing. The servo piston isn't moving, so no forward motion. But as you say, is it because no feedback, so no movement? The repair manual says forward motion is still possible so that might not be it.

I swapped out the Check and Relief High Pressure Valves. Still had reverse and no forward. They both looked good.

I don't have any gauges to test with. I could probably pick up a gauge and hose from Northern Tool and rig something up. I believe the forward test port is right under the forward check and relief valve.

I'm leaning towards the servo piston being the culprit.

 

[KarlAmherst]

I've been studying the WSM a little more and think I'm on the right track with the servo piston.

The servo piston is directly linked to the swash plate. The servo piston is supposed to move up, down and neutral.
If I am right, it's moving up and neutral, but not down.
The owner of this tractor told me the services were waaaayyy overdue.
I'm guessing the servo piston has become stuck because of particles in the hydraulic fluid.

Anyone ever worked on the servo piston? The WSM shows the swash plate riding in a groove on the servo piston so it's not coming out without taking a lot of stuff apart.
There is a little plate on the bottom of the transmission directly below the servo piston. Anyone have experience with taking this plate off and working on the servo piston?

 

[North Idaho Wolfman]

You don't have a 2 you either have a 1, or 3 they didn't release the 2 in North America.
If you give me the serial # I can tell you which one you have.

 

[200mph]

An easy way to tell if it is a -1 or -3 is to look at how the PTO engages. -1 uses a lever/cable arrangement, while -3 will have a rotary electric switch.

 

[KarlAmherst]

I'm down to the last component to check and then I'm done. With no specialized tools there is only so much troubleshooting that can be done.

I've attached two pictures. One is the Forward hydraulic circuit and one is the Reverse hydraulic circuit.
The item labeled (15) in the pictures is called "Spool (Pressure Selector)".
The diagrams show the fluid taking two different paths through this spool.
One path is for FWD motion and the other path is for REV motion.
There is also a "Hi-Lo Spool". (14).
Any idea why the 2 spools?
The Hi-Lo spool has a solenoid valve and a Hi-Lo spool valve. Seems like the Hi-Lo is taken care of right there.
Spool Pressure Selector seems to pertain to FWD and REV in the diagrams.

 

[Cig]

Greetings all,
I am working on a friends L5240.
The problem is that it will only go backwards and not forward.

I started the tractor in Mode "A" test mode and observed T1-T16.

The only thing that did not check out was T12 Swash Plate Position Sensor Voltage.

Pressing the pedal in reverse showed a rise in voltage and the tractor moved backwards.

Pressing the pedal forward did not show an increase in voltage and the tractor did not move forward.
Forward should have displayed between 2.90-4.56(V).
Volts were steady at 2.5.

I pulled the error codes and got
81,82,87,90,91
(81) HST Pedal Sensor Failed
(82) Swash Plate Position Sensor Failed
(87) Tachometer
(90) HST Proportional Valve Forward Failed
(91) HST Proportional Valve Reverse Failed

Troubleshooting, I switched the connectors at Proportional Forward and Reverse Valves.
Pressing the pedal forward resulted in the tractor moving backwards.
Pressing the pedal backwards had no effect.
That lead me to believe the pedal sensor is okay.

I physically switched the proportional valves.
Same effect. Tractor moved backwards when the pedal was moved forward.
I switched the connectors and the tractor moved backwards when the pedal was pressed back.

I'm thinking the pedal sensor is good, the proportional valves are good.
Did I miss something? What should I check out next?

Did u get this repaired, I have al5740 doing same thing .would like to know what the fix was

 

[Orange fever]

Did u get this repaired, I have al5740 doing same thing .would like to know what the fix was

I know this thread is very old and very dead, but I just fixed my L4240 with the same issue. It would only move in reverse. All other hydraulics worked as they should. It ended up being the proportional solenoid/regulator valve located on the right side of the hydrostat right behind the step. Part number TD170-59310.