eHydro -- No reverse in 2WD

[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.