3x20 3520 eHydro Problem No Reverse No Error Codes Forward works Fine Please Help!

[CobraTom]

Good day all,

I am having issues with my John Deere 3520 tractor. The tractor runs fine in forward, but has no reverse.

At first I thought it was a electrical problem, like the pots, or MFWD sensor, but after tracing all the connections down to the two solenoids, everything appears electrically fine. The tractor sees +12V to each forward and reverse solenoid. The solenoid see 4.7 ohms resistance across each, so it appears those too are fine.

However, the tractor does not switch to reverse. Is there another condition that needs to be met somewhere else for reverse to kick on? Does anyone have any diagrams or service manuals related to the HST unit? My understanding is its manufactured by Danfoss Sauer and requires the tractor to be split to service the unit in any way.

Thanks in advance for any assistance.

 

[beenthere]

Deere has a service tech manual available to you.. from Deere dealer, on their internet site, as well as can find them on eBay.

Or seems a visit to your Deere dealer would get you some answers as well as they could make copies of parts of the service manual if they want to do that for you.

And a TBN member will very likely help you out too.

But I wouldn't want to be without the service tech manual for what it does for me.

 

[Dan Hunter]

This probably won't help but I'll post it anyway. My 3720 wouldn't back but would go forward. My problem was a stick under the floorboard. I believe it was sensing and accepting the forward pedal depressed constantly at some level but got upset when I pushed the reverse pedal as it then sensed both pedals being pushed. Anyway, my solution was as simple as removing the stick.

 

[arlen4720]

Good day all,

I am having issues with my John Deere 3520 tractor. The tractor runs fine in forward, but has no reverse.

At first I thought it was a electrical problem, like the pots, or MFWD sensor, but after tracing all the connections down to the two solenoids, everything appears electrically fine. The tractor sees +12V to each forward and reverse solenoid. The solenoid see 4.7 ohms resistance across each, so it appears those too are fine.

However, the tractor does not switch to reverse. Is there another condition that needs to be met somewhere else for reverse to kick on? Does anyone have any diagrams or service manuals related to the HST unit? My understanding is its manufactured by Danfoss Sauer and requires the tractor to be split to service the unit in any way.

Thanks in advance for any assistance.

You need to put your tractor in the diagnostic mode, then you can see the raw sensor values on your display. I bet it's not seeing the reverse pedal pot. You will be able to see all the voltages of all the sensors, and the current to the forward and reverse servo valves.
It's pretty **** handy.
I'll post the info for a 4x20 eHydro. It should be close to what you have. You should get a tech manual for your specific tractor.
You basically enter diagnostic mode 1 by using the display mode switch and the blinker switches to enter the password. Then you can view the ICC, TCU, ECU computer registers.
You'll want to be looking mostly at the TCU (Transmission Control Computer) registers.
You will have your problem isolated in minutes.
If you do need to tear into the eHydro, You'd be the first I've heard of having a problem.
Your are right, it is made by saur danfoss in their Ames Iowa plant. Deere has been using them for over 10 years with very little trouble.

 

[CobraTom]

You need to put your tractor in the diagnostic mode, then you can see the raw sensor values on your display. I bet it's not seeing the reverse pedal pot. You will be able to see all the voltages of all the sensors, and the current to the forward and reverse servo valves.
It's pretty **** handy.
I'll post the info for a 4x20 eHydro. It should be close to what you have. You should get a tech manual for your specific tractor.
You basically enter diagnostic mode 1 by using the display mode switch and the blinker switches to enter the password. Then you can view the ICC, TCU, ECU computer registers.
You'll want to be looking mostly at the TCU (Transmission Control Computer) registers.
You will have your problem isolated in minutes.
If you do need to tear into the eHydro, You'd be the first I've heard of having a problem.
Your are right, it is made by saur danfoss in their Ames Iowa plant. Deere has been using them for over 10 years with very little trouble.

Thank you for everyones help. I guess I should explain a bit further. I have at first reversed the pots on the pedals (plugged fwd to rwd) and I was able to use the rwd pedal to go forward, but the fwd pedal did not move the tractor in reverse.

I have isolated the wiring, and have it exposed at the harness from the coils. I am able to start the tractor and apply +12V direct to the coil on the HST and move the tractor forward. If I apply +12V to the reverse coil, I do see a amperage draw on my multimeter, but the tractor does not move in reverse.

I am assuming at this point I have a clog or debris in the reverse valve. Are any of the ports on the HST pump that are accessible via the bellhousing close enough to the reverse valve that I can flush it?

 

[Cocre]

I highly recommend that you buy the technical manual. It is easily worth the cost, even if you use it for nothing else but to better understand the operation of the machine. It is a work of art.

It appears to me that to get to the proportional and relief valves the tractor has to be split.

There are pressure test ports on the right side of the clutch housing. The right hand brake bellcrank has to be removed to get to them. Top port is forward, bottom port is reverse.

From the 3x20 technical manual.

Symptom: Machine Will Not Move in Reverse
Problem Cause - Solution
1. Machine moves in Forward only.
a. HST Check reverse pedal position sensor for calibration or malfunction. Repair or replace sensor.
b. Auto HST Check D-N-R switch and wiring to forward and reverse proportioning valves.
c. See Symptom: Machine Will Not Move In Forward or Reverse above.
2. Reverse proportional valve malfunctioning.
a. Replace valve.
3. Directional relief valve stuck open.
a. See Hydrostatic High Pressure Relief Test on page 661.
b. Replace relief valve.

 

[CobraTom]

I highly recommend that you buy the technical manual. It is easily worth the cost, even if you use it for nothing else but to better understand the operation of the machine. It is a work of art.

It appears to me that to get to the proportional and relief valves the tractor has to be split.

There are pressure test ports on the right side of the clutch housing. The right hand brake bellcrank has to be removed to get to them. Top port is forward, bottom port is reverse.

From the 3x20 technical manual.

Symptom: Machine Will Not Move in Reverse
Problem Cause - Solution
1. Machine moves in Forward only.
a. HST Check reverse pedal position sensor for calibration or malfunction. Repair or replace sensor.
b. Auto HST Check D-N-R switch and wiring to forward and reverse proportioning valves.
c. See Symptom: Machine Will Not Move In Forward or Reverse above.
2. Reverse proportional valve malfunctioning.
a. Replace valve.
3. Directional relief valve stuck open.
a. See Hydrostatic High Pressure Relief Test on page 661.
b. Replace relief valve.

Thank you for the awesome information. I did not even think about the directional relief valves. I have a technical manual on cd ordered but my dealer here tells me I won't see it for another 2-3 weeks as its coming out of the states.

Any chance you can take a screen shot or a photo of the location of the reverse relief valve on the hst unit in the technical manual? I can definitely touch the lower proportioning valve by squeezing my hand in from the opening underneath the tractor. If the relief valve is close, I can easily use a allen key to remove it.

Thanks again!

 

[Cocre]

Well, I tried to insert some pictures but it just won't happen. I browse and select the files, click upload, and wait a few seconds and the popup box closes, but no inserted pics. Must be doing something wrong.

 

[beenthere]

Cocre
Click the "go advanced", then the "manage files", then click "Add file", browse and find the pic you want, then click the "Upload file".
Maybe that is what you are doing, but that sequence works for me. I do recall getting the symptom you mention.. but for the life of me cannot remember what I was doing wrong.. seems I was not clicking on "upload" to finish the cycle.

 

[Cocre]

Must be something wrong with TractorByNet. I tried all methods with three different browsers. Chrome even shows the percent upload in the lower left of window, the files upload, then some more responses in lower left but no files.