Deere 4400 low charge pressure, won't move

[kennyd]

Is the range lever still working? They did have some issues with the shaft breaking right where is enters the case.

The brake return springs where also known to fail, and the shafts to rust up where they enter the case causing the brakes to lock on, but that does not sound like you issue in what I've read so far.

 

[dustin63933]

If steering is working it is highly unlikely the pump is the problem.

Yes teeing into the line from the cooler should show similar 30 PSI.

Yes on suspecting a problem inside the transaxle HST assembly. If pure mechanical control the HST should try to move even with low charge. Would probably be noisy but still should try.

Will the tractor roll like in neutral or do you still have the HST braking effect?

It will roll in neural and once you put it in gear it’s hard to roll. But yeah when I push the pedal down the charge pressure goes from 30 to about 15 and the tractor doesn’t even twitch, the engine changes very slightly that’s about it.

 

[dustin63933]

Is the range lever still working? They did have some issues with the shaft breaking right where is enters the case.

The brake return springs where also known to fail, and the shafts to rust up where they enter the case causing the brakes to lock on, but that does not sound like you issue in what I've read so far.

Oh yeah lol I’ve had both of those issues happen to me in the past but fixed them. The lever does shift into all gears and tractor won’t move in gear.

 

[oldnslo]

Studying the schematic it shows case drain lines for both the pump and motor. Light blue lines on schematic. I tried looking at Deere parts diagrams but I could not determine if these are external lines or just drain directly into the transaxle housing. If external and accessible can you pull one off and check for flow? With tractor not moving it should be minimal again per the schematic.

The pressure being low in neutral is concerning since the charge flow is going somewhere. Pressure changing when trying to move is this in both directions of travel or just forward or reverse?

Out of curiosity what range pressure gauge are you using to measure the charge pressure? I hope not the 10,000 PSI unit in the picture

 

[dustin63933]

Studying the schematic it shows case drain lines for both the pump and motor. Light blue lines on schematic. I tried looking at Deere parts diagrams but I could not determine if these are external lines or just drain directly into the transaxle housing. If external and accessible can you pull one off and check for flow? With tractor not moving it should be minimal again per the schematic.

The pressure being low in neutral is concerning since the charge flow is going somewhere. Pressure changing when trying to move is this in both directions of travel or just forward or reverse?

Out of curiosity what range pressure gauge are you using to measure the charge pressure? I hope not the 10,000 PSI unit in the picture

From what I can tell the case drains do just drain back into the transaxle housing and I don’t think their lines it’s just small clearances that allow it to bypass by design.

Yeah I’m using a 300psi gauge to measure charge pressure. I’ve tried 2 different gauges and both measured correctly when I hooked them to my air compressor.

The charge flow drops in both directions of travel. I’m going to try to shim the charge relief valve Sunday and see what that does. Thank you for your reply,

 

[oldnslo]

Be careful increasing the charge pressure since both the filter and cooler will see the increased pressure and if go to high could damage one of those items.

Is there any type of inspection plate that you can remove on the transaxle to look for oil flow while tractor is running?

I know this is preaching to the choir but The big unknown is where is the charge flow going at this time or why did it suddenly lose charge pressure.

Since fails in both directions that eliminates the high pressure reliefs as cause since both would have to fail.

Potential leak points:
Charge relief stuck full open.
Some internal charge passage component failure like O-ring, tube split, etc. my suspicion but no clue how the charge circuit is plumbed on that HST.

Either pump or motor has major internal leak doubtful but possible could fail that suddenly.

Broken gear or mechanical failure should not change charge pressure.

 

[Harry in Ky]

So you've established there is 30 PSI charge pressure (until you stroke the transmission) but do you know what it SHOULD be? That seems pretty low to me. Where does the charge pressure enter the transmission? Is it simply a line threaded onto a fitting in a port on the case somewhere? Can you access that with some compressed air? You might try that with hydraulic filler cap off. Charge it with air and see if it shows some resistance or simply blows out into the case.

 

[oldnslo]

Harry
Per schematic the OP had in the attachments on his first post charge relief is 100 - 150 PSI so this system is way low. The unknown is why and how to diagnose.

 

[rScotty]

Just following along. Wish there were a few more test points or connections where a T could be inserted.

I haven't spent the time with the diagrams that others have, but are there some diagrams missing? where does the pressure from the Power Steering go? All I see is "transmission tunnel". What does that mean?

Is there a more formal schematic? There are many parts not shown. A pictorial is always limited by the understanding of the artist

On the second diagram is the feed to the cooler and filter by suction? Or is it under slight positive pressure from that line in the first pictorial which goes to the "transmission tunnel?

It seems to me that the 30 ps you are measuring says that the charge relief valve is doing its job, although I am not exactly clear on where that 30 psi is generated which you are seeing measured at the test points?

I would not shim the charge relief. As far as I see, all the charge relief valve does is to prevent an internal leak in the HST pump from back-pressuring the fiter and cooler....both of which cannot handle much pressure.

My conclusion is that either the HST pump is not generating the pressure to feed to the HST motor, or else the System Relief valve(s) are not allowing that pressure to reach the motor.
Can you service the System Relief Valves or look for a crack in the pressure feed to those relief valves?? Those are my #1 culprit. In spite of their being two of them, they may have an internal pipe or passage in common.
And just to eliminate the HST pump - which I do not expect to be the problem but it needs eliminating as a possbility.....so is there some way to insure HST pressure at the pump outlet?

rScotty

 

[Harry in Ky]

Okay, I see the pressure listed. I still maintain an air check would be helpful. I too suspect an internal leak, but I'm not sure there's any easier way to confirm that. If the leak is indeed internal, it really doesn't matter just what it is, it has to come apart one way or the other. Yes a flow meter measuring the flow and pressure available at that port would confirm that the supply is adequate, but I'm guessing supply is not the problem. He probably doesn't have access to a meter anyway.