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?