eHydro -- No reverse in 2WD

[mike48130]

The swash plate is inside the pump. The angle of the swash plate controls the stroke of the pump pistons, and thus the output of the pump. There are plenty of Google articles if you care more. I looked at the 3320 parts diagram to see what was different than the 4x10 series, and didn't see much different. I didn't find any dump valve. There is a SCR valve now on the transmission which I am not sure what it is, but I speculate it is just an over pressure relief for the hydrostatic system.

All the load match does is reduce the output speed of the transmission to maintain a constant RPM and engine load. Basically keeps you from stalling it out. Maybe with the engine RPM low enough, the load match does not work properly, never tried it. I leave mine on, it is just better for the tractor. The new series have more HP, so it is needed less, but on my 4210 at 28HP, you can bog down the machine pretty quick with it off, especially going up hills.

Since you said you will be doing an overhaul on the hydraulics, I would really spend some time making sure you know what works and what doesn't, and how it works. The oils and such can hit the pocket book hard, and somethings you need to drain the oil to get to, so doing all at once is much better.

 

[texasranger556]

This has been bugging me, so I looked through the 3220 parts diagrams. The SCR Mike mentions look to me like the normal high pressure relief valves. One for forward and one for reverse. In my 4400 service manual they are called "System Relief Valves", and they open at 6000-6200 psi. They each have a check valve also that allows charge pressure (150 psi) to enter the low side of the high pressure pump to prevent cavitation. Maybe the team who wrote the parts diagram used "System Charge Relief" or some variation. In any case Mike, your 4210 has them too.

Now how could engaging mfwd have any affect on forward motion from a hydraulic standpoint? I can't see any link. The parts diagram suggests the mfwd is engaged manually with a lever. The owner's manual I found shows a lever rather than a button. So I don't see any way that the hydrostatic system could behave differently if the mfwd is engaged or not. Hydraulically.

The owner's manual mentions a dash light when mfwd is engaged. So there could be some change in the electronic control of the hydrostatic transmission as a function of mfwd engaged or not. Seems a stretch though.

Do you have any way to get someone to video you driving the tractor illustrating the behavior you describe? In your original description, backing up with several hundred pounds in the bucket is the PERFECT opportunity to spin the rear wheel(s) when in 2wd. Have you tried engaging the diff lock in that instance prior to engaging the mfwd?

I'll echo Mike's words that you can't have front wheel drive ONLY without some sort of mechanical failure in the rear end of the tractor (broken shaft, gear, diff, axle, etc).

Something still isn't adding up...

 

[mike48130]

Now how could engaging mfwd have any affect on forward motion from a hydraulic standpoint? I can't see any link. The parts diagram suggests the mfwd is engaged manually with a lever. The owner's manual I found shows a lever rather than a button. So I don't see any way that the hydrostatic system could behave differently if the mfwd is engaged or not. Hydraulically.

The owner's manual mentions a dash light when mfwd is engaged. So there could be some change in the electronic control of the hydrostatic transmission as a function of mfwd engaged or not. Seems a stretch though.

I believe they use the same 4WD engagement as my 4410, a electric solenoid that controls the hydraulic cylinder for the 4WD engagement. The cylinder is actually spring loaded, and the spring engages the 4WD automatically, and the hydraulic pressure pulls the lever out into 2WD. The default is 4WD. The reason that is kind of important, is that the 4WD cylinder is off of the front pump that feeds the power steering, 4WD, and hydrostatic charge pressure, so there could be an issue tying them all together.

On mine, the 4WD light is in the switch, so as soon as you hit the switch, the light comes on. It does not actually show that it engaged, just the switch position. I thought the 3320 was the same, but they moved the light to the dash instead of the right rear console.

But I agree, the symptoms are confusing. I am going thru something similar on my Bobcat, where I thought I knew what the symptoms were, but when I tore it apart, there was nothing wrong. Now I am questioning what I thought was the issue, and if I did enough diagnostics before opening it up.

 

[texasranger556]

I believe they use the same 4WD engagement as my 4410, a electric solenoid that controls the hydraulic cylinder for the 4WD engagement. The cylinder is actually spring loaded, and the spring engages the 4WD automatically, and the hydraulic pressure pulls the lever out into 2WD. The default is 4WD. The reason that is kind of important, is that the 4WD cylinder is off of the front pump that feeds the power steering, 4WD, and hydrostatic charge pressure, so there could be an issue tying them all together.

On mine, the 4WD light is in the switch, so as soon as you hit the switch, the light comes on. It does not actually show that it engaged, just the switch position. I thought the 3320 was the same, but they moved the light to the dash instead of the right rear console.

But I agree, the symptoms are confusing. I am going thru something similar on my Bobcat, where I thought I knew what the symptoms were, but when I tore it apart, there was nothing wrong. Now I am questioning what I thought was the issue, and if I did enough diagnostics before opening it up.

I totally understand what you are saying, but I think the 3320 engages the mfwd manually rather than a solenoid like your 4410.

Your user manual shows a rocker switch on the fender:
OMLVU13193_H2

The 3320 shows a knob to the left of the seat, which makes me think mfwd engagement is not using hydraulic pressure at all:
OMLVU17926_J7

My 4400 is a lever behind my left foot, roughly the same angle to the transmission case as the knob on the 3320.

If anyone can verify, I'd be interested to know for sure.

 

[Millalien]

I didn't find any dump valve. There is a SCR valve now on the transmission which I am not sure what it is, but I speculate it is just an over pressure relief for the hydrostatic system.

All the load match does is reduce the output speed of the transmission to maintain a constant RPM and engine load. Basically keeps you from stalling it out. Maybe with the engine RPM low enough, the load match does not work properly, never tried it. I leave mine on, it is just better for the tractor.

Super, thanks.

I suspect that the "dump valve" he was referring to is the SCR valve - that seems to be closest to affecting the function he was trying to describe, except that it diverts in 2WD Load Match OFF when the RPM is too low. The issue I have only pops up when the Load Match is OFF - everything seems to work as usual with Load Match ON. I also never intentionally run the machine with the LM off - this all came up b/c I inadvertantly flipped the rocker switch off and disengaged 4WD and discovered that the rear axle loses power with the slightest load.

 

[mike48130]

I totally understand what you are saying, but I think the 3320 engages the mfwd manually rather than a solenoid like your 4410.

Your user manual shows a rocker switch on the fender:
OMLVU13193_H2

The 3320 shows a knob to the left of the seat, which makes me think mfwd engagement is not using hydraulic pressure at all:
OMLVU17926_J7

My 4400 is a lever behind my left foot, roughly the same angle to the transmission case as the knob on the 3320.

If anyone can verify, I'd be interested to know for sure.

Wow, I just looked at the parts manual, and it looks like they went back to the manual shift MFWD and PTO as well. Cost saving passed onto the customer I'm sure!! I guess there's something to be said about keep it simple and it just works. A lot less to go wrong.

 

[Millalien]

Wow, I just looked at the parts manual, and it looks like they went back to the manual shift MFWD and PTO as well. Cost saving passed onto the customer I'm sure!! I guess there's something to be said about keep it simple and it just works. A lot less to go wrong.

On the 3320 the 4WD/2WD drive is engaged with a lever located under and to the right of the driver's seat and when engaging it feels like it's mechanical rather than actuating a solenoid; there's a dashboard light to indicate when 4WD is engaged.

The problem I have is that I don't think I've ever operated the machine in 2WD with Load Match off previous to doing it accidentally at the start if this thread. I do recall toggling it off when operating the FEL and finding that the tractor was quick to stall, but since I'm hardly ever in 2WD while FEL'ing, my guess is that I wasn't in 2WD. I did that years ago when fooling around with load match to see what it did and I figured out pretty quick that it's best just to leave it on.

The symptom feels and sounds consistent with a valve opening to divert fluid from the transmission if the RPM isn't sufficient to drive the pump enough to overcome the load's inertia. If I juice the RPM, the valve doesn't open and 2WD works as normal. Why that valve doesn't open in 4WD is baffling, but I think the valve's function actually relates to the Load Match system controls and it's behavior when that system is off is an unintended side effect - it prevents the tractor from stalling in 2WD only by diverting fluid if the RPM isn't sufficient, but I'm not sure that there's a design reason for that. It also feels like it ought not to be "dumping" at that point and that there's something out of whack someplace.

I'll try to capture a video myself and post that.

 

[texasranger556]

The only electronic control of the transmission that I see from parts diagram is the two proportional valves which control the position of the swash plate. So this "dump valve" that the dealer is talking about doesn't exist in a physical sense, it's all part of the algorithm that the computer is using to control the swash plate position.

I'll watch for your video...maybe there is something being overlooked.

When you seemingly lose power in 2wd, does the transmission make a chattering noise at low RPMs?

 

[Millalien]

When you seemingly lose power in 2wd, does the transmission make a chattering noise at low RPMs?

No chattering now, but I have had that - I was towing a light load one real hot summer day in 2WD and got some chatter at one point, which I attributed to over heated hydro fluid. I shut it down, dropped the load, let everything cool off, and haven't heard a peep since. Now that you mention it, missing link on this story maybe?

 

[texasranger556]

When my charge pressure regulator was screwed up on my 4400, transmission had what I would call a chatter which was the hydrostatic pump cavitating due to low charge pressure. At engine idle just after starting the tractor you could mash the hydro pedal to the floor and tractor would not move, then jerk a little. High RPMs it would drive ok but sounded "off" compared to the 4300 I also had. I could feel some vibration in the hydro pedal. Once the charge pressure regulator was fixed, drives like new. Unfortunately that was AFTER we had split the tractor and resurfaced the hydro pump valve plate. No harm, it only cost time.

Since your hydro is fly by wire, it would be much harder to detect by feel. And you may not realize the sound being off without another reference point. If it was my tractor, I would measure the charge pressure just for piece of mind. If it's low, you could erode the valve plate and piston block over time which leads to $$$$.

A chatter in the transmission could also be gears or bearings. If it happens again take some video.