eHydro -- No reverse in 2WD

[Millalien]

I've suddenly got no power in reverse while in 2WD on my 2008 3320 eHydro and limited forward power - the machine will back up a few feet then stop; forward is sluggish. In 4WD, forward and reverse as normal. I've been running in 4WD for the past month or more without shifting out and I don't know when this problem started - I wouldn't have noticed it at all had I not accidentally knocked the machine out of 4WD a couple of days ago.

I'm guessing that the 4WD isn't really "as normal" either and that the rear axle is malfunctioning, but I've don't know the first thing about how the hydrostatic drive systems work and I'm not too keen on tearing anything apart until I've got some idea of what it is I'm looking for.

So...how does the darn thing work?!

 

[Spindifferent]

Just to rule out the obvious and troubleshoot:

Have you checked the hydraulic fluid level to make sure it has the correct amount?

Any error codes?

Does the 3 point work appropriately?

If you have a loader, how does the loader function?

Did you perhaps depress the forward and reverse pedals at the same time?

Have you read this thread?
http://www.tractorbynet.com/forums/...ating/342356-3x20-3520-ehydro-problem-no.html

 

[Millalien]

Just to rule out the obvious and troubleshoot:

Have you checked the hydraulic fluid level to make sure it has the correct amount?

Any error codes?

Does the 3 point work appropriately?

If you have a loader, how does the loader function?

Did you perhaps depress the forward and reverse pedals at the same time?

Have you read this thread?
http://www.tractorbynet.com/forums/...ating/342356-3x20-3520-ehydro-problem-no.html

Thanks for the thread link - I came across that last night as well.

Fluid levels are good; 3 PT, loader and BH all work; and I'm operating the pedals correctly.

I'll check electrical, but since the machine starts to reverse and then quits, and it's forward power to the rear axle is weak, I'm thinking it's related to the plumbing and not the electrical.

The part that's most curious to me is why it's affecting the rear axle only, which if this were a conventional system would suggest a rear differential failure. But there again, the hydrostatic system is a big black box to me.

 

[Spindifferent]

A mystery for my very limited knowledge. Hopefully there are experts here that can help. Otherwise, a trip to the dealer may be in order.

Please let us know what you eventually find out.

 

[mike48130]

If this is the same as the 4x10 series than the front hydraulic pump feeds the power steering, the charge pressure for the hydrostatic trans and the 4wd and pto shifters.

That being said I bet you lost the charge pressure to the hydro trans. The question is why. I would put a pressure tester on it and see what it is in 2wd and 4wd. Then assuming the 2wd is low you need to find out why.

So the pressure is in a loop for that circuit. The charge test port is on the solenoid block on the right side of the tractor around the loader valve. Outside of the load valve and easy to get to.

So the 4wd works by a hydraulic cylinder controlled by a electric solenoid valve. The cylinder has a springing it and is automatically in 4wd due to the spring force. When the hydraulic pressure is applied it pulls it out of 4wd tp 2wd. That being said, when you are in 2wd you are changing the flown and pressure of the charge fluid.

I would guess your charge pressure relief need to be cleaned or adjusted ot your 2wd solenoid has a leak so when you put it in 2wd the charge pressure is leaking down back to the reservoir assuming you have no leaks.

A quick test is to have some one work the 4wd switch while the tractor is running and watch the 4wd cylinder on the left rear tunnel under the seat just in front of the left rear axle housing. If that is actually moving that that tells you something.

The light on the switch is only electrical power to the switch and doesn't verify functionality.

I think there is a 4wd system that used a dual acting cylinder and not the spring but I don't know if that is the older design or newer.

You could have a leak in the solenoid valve or the cylinder that is causing flow by and charge pressure loss.

Charge pressure is usually around 190psi. It changes slightly maser on tractor model but us usually low so any flow by will cause the pressure to drop quick.

 

[Millalien]

That being said I bet you lost the charge pressure to the hydro trans. The question is why. I would put a pressure tester on it and see what it is in 2wd and 4wd. Then assuming the 2wd is low you need to find out why.
...

I would guess your charge pressure relief need to be cleaned or adjusted ot your 2wd solenoid has a leak so when you put it in 2wd the charge pressure is leaking down back to the reservoir assuming you have no leaks.

Thanks for the anatomy lesson - very helpful!

And consistent with symptoms - what I discovered yesterday was that the power loss in reverse occurs under load and can be restored until re-loaded. The sequence of events is something like this: 1. In 2WD, operating normally until there's a substantial payload, e.g., a few hundred pounds in the FEL or a pulling a few hundred pounds from the front end while in 2WD reverse. 2. When loaded, the machine suddenly loses power to the rear axle, and will then only reverse few feet and quit reversing. 3. Flip into 4WD, machine's capacity is restored forward and reverse, except that the rear wheels do not appear to have any drive. 4. Run the machine in 4WD unloaded for a bit. 5. Flip back into 2WD, machine runs as normal and back to #1 above - de-powers when loaded and the cycle starts anew.

Seems like the charge relief in 2WD is malfunctioning, like its sticking on while charged. Perhaps the torque load in reverse in different enough from forward that there's enough charge when malfunctioning for forward motion, but not reverse.

I don't have a hydraulic pressure gauge, also assuming that tool would be a kit with multiple adapters. Never not a reason to buy more tools ... !

 

[mike48130]

This statement confuses me "3. Flip into 4WD, machine's capacity is restored forward and reverse, except that the rear wheels do not appear to have any drive"

The front and rear drives are connected by gears, so if 4wd is engaged, the front can not work without the rear. The rear can not loose drive without the front not having drive. Not sure if tis is the case, but need to verify it.

I would suspect you have a leak in the 4wd hydraulic system. Wither in the cylinder or the solenoid.

I buy my hydraulics from Surplus Center. Pretty cheap for standard stuff. I don't recall what the fitting sizes are on the manifold block for testing the pressure. I have them, and just used them, but don't recall the size. JD uses a bunch of metric sizes.

 

[Millalien]

The front and rear drives are connected by gears, so if 4wd is engaged, the front can not work without the rear. The rear can not loose drive without the front not having drive. Not sure if tis is the case, but need to verify it.

Well, if the axles are gear driven (assuming then that there's a transfer case that hydrostatic and that's where the plumbing stops), then this is peculiar.

Normally, the tractor doesn't lose traction running up grades on the 1000' of bad maintenance which is my gravel driveway. Since the malfunction arose, the front wheels lose traction and skip, and forward progress halts with the skipping - there doesn't appear to be any push from the rear wheels. Also, I nearly got stuck backing up a slight grade on soft soil when the front wheels lost traction and there was no pull from the rear wheels. So under those circumstances the machine is behaving very much like a front-wheel drive only car. None of those symptoms are 'normal' in my experience with the machine. I've certainly had sticky situations where I've buried the front axle and had rear-wheel spin, but not the opposite as far as I can recall and I can't recall ever having the uphill, front wheel skipping problem on my driveway before.

So, yes, hard to explain.

 

[mike48130]

Well, I think that changes everything. I assume it is the same in all 3 ranges. The front axle is driven by the out put shaft of the range gears and so is the rear differential. If you are getting FWD in all ranges, than there is a break in the system between the range gear shaft and the rear wheels.

In between this range output shaft (the counter shaft on JD parts diagram) and the axle shafts you have the rear differential. So it sounds like you don't have a hydraulic issue, but a mechanical one.

You need to find the broken link. It can be the input shaft to the differential, something inside the differential, a gear, or axle shafts.

Did you notice anything loud are hard, or just didn't notice until you took it out of 4WD. I suspect you have been running in front wheel drive for some time.

It appears the counter shaft is the differential pinion shaft, and also looks like it feeds the FWD. So I would expect something in the diff. It sound like you need to pull the rear cover and look inside there. You need to drain the hydraulic oil to do that. I do not see anything external or simple that would allow the front wheels to drive and the rears to slip.

I would be cautious on how you use the tractor. You are putting all the torque to the front drive system, which it is probably not designed for. You have the chance to cause a lot more damage driving it.

 

[mike48130]

I assume it's out of warranty?

 

[Millalien]

... So I would expect something in the diff. It sound like you need to pull the rear cover and look inside there. You need to drain the hydraulic oil to do that. I do not see anything external or simple that would allow the front wheels to drive and the rears to slip.

I would be cautious on how you use the tractor. You are putting all the torque to the front drive system, which it is probably not designed for. You have the chance to cause a lot more damage driving it.

My thinking centered on a rear diff failure but my ignorance of how the eHydro works confused me ... your comments have been a great help and it's making sense.

Sound advice on the machine out of service, as well. It's heading to the tractor shop on Monday ... too much of this is beyond my shade tree capacity. Seems like the kind of problem that requires the attention of someone who knows what looks right and what looks wrong, in this case that someone isn't me.

 

[Millalien]

I assume it's out of warranty?

Bought new in 2008, has about 500 hours ...I think the power train was 6 years / 2000 hours, but I'll check with Mr. Deere.

 

[mike48130]

Good luck and let me know how it turns out.

 

[Millalien]

I got the tractor back from Deere yesterday afternoon after a week of fretting about a big ticket repair item.

The service guys got it fixed and charged me nothing.

Because as soon as they turned Load Match back on, the problem went away.

Apparently, after ten years of never touching that rocker switch (always on), I must have nudged it off recently and immobilized the tractor in 2WD with the slightest of loads, including traveling unloaded up a 9% grade.

Glad to have the machine back for $0 - a little irritated that I didn't flip that rocker before hitting the panic button.

Also, it's peaked my curiosity about the eHydro system - I'm assuming that to operate without the Load Match the throttle must need to be set high (>2k RPMs) to prevent the dump valve from from killing the transmission under load. The service manager said that the applications where the Load Match could be off would be plowing and towing, which I guess would be steady-load examples where the throttle is set high and stays there.

Anyway, I appreciate the responses here - really helps me understand the machine better and that's a good thing, as is a $0 repair invoice.

All's well that ends well.

 

[Spindifferent]

Thanks for letting us know the resolution.

Glad it worked out to be no cost!

 

[mike48130]

Well I hope it is fixed but you symptoms don't match the fix. That load match does not affect 4wd on power loss. It actually just keeps you from bogging down the engine and stalling it under very heavy loads.

I would verify it bis working right and you have power in 2wd and to all 4 in 4wd.

 

[Millalien]

I would verify it bis working right and you have power in 2wd and to all 4 in 4wd.

With Load Match OFF in 2WD and throttle set at 2k RPMs the machines does NOT lose power to the rear axle. With throttle at 1500 RPMS and under load in 2WD, the transmission dump valve is tripped and power is diverted. I verified this on snow & mud and there's no doubt I had drive to the rear axle in 2WD with Load Match ON at any RPM and with Load Match OFF at > 2k RPM, as well as power front and rear in 4WD with Load Match ON.

According to the service manager, the Load Match system includes both throttle and flow control, with a transmission dump valve being flow control which trips when Load Match is OFF to recirculate fluid rather than drive the axle. It's a system to match both hydraulic flow and throttle to load, with the dump valve being a fail-safe system which re-circulates the fluid if the throttle doesn't "match" the load, which could be the case when Load Match is disabled and the throttle is set too low. This seems a little counter-intuitive to me, but that's the way it works.

He didn't explain why I didn't lose power to the front axle in 4WD with Load Match OFF, but as a practical matter everything is working fine (as long as I juice the throttle when Load Match is off). I suppose the dump valve could be out-of-spec and dumping too soon, but we'll take a look at that during a regularly scheduled maintenance break in a few months. My local tractor mechanic can check pressure at various ports and figure out if something ain't quite right.

Thanks again for your help on this.

 

[mike48130]

It sounds like maybe they changed the design a bit for the newer ones, seems to work different than mine. Good to hear it's working.

 

[texasranger556]

I'm interested in this "dump valve". I suspect they just mean the servo controlling the swash plate simply de-strokes to maintain engine RPM, but my 4400 is from the pre-electronic control stone ages so haven't had the joy of dealing with the new "features". I can stall the engine whenever I want .

I agree the "fix" doesn't match the symptoms of lost drive in 2wd but 4wd is fine (without wheel spin). There has to be more to the story on that front.

 

[Millalien]

I'm interested in this "dump valve". I suspect they just mean the servo controlling the swash plate simply de-strokes to maintain engine RPM, but my 4400 is from the pre-electronic control stone ages so haven't had the joy of dealing with the new "features".

I don't know what a swash plate is...please explain more if you have a minute.

The service guy called it a "dump valve" but I'm not sure that's the correct technical term, first of all, secondly I don't really agree with him that there's nothing wrong with the system as whole, but I was able to prove that the 2WD power loss with Load Match off disappears if the throttle is set high and in any case I have power to all four wheels with Load Match ON in 4WD.

What he said was that the "dump valve" diverts fluid if the pressure is too low so that the engine doesn't stall, which doesn't really make sense when the Load Match is OFF. Drilling into the engineering with him wasn't getting me anywhere so I just loaded up and moved on.

Still planning on a hydraulic overhaul when the weather's better and we can take the machine out of service for a few weeks.