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The right Hydro-Gear ZT3100 drive has become weak in reverse. The tag on the drive is below


I thought to check the hydraulic fluid reservoir (which supplies both left and right drives) and found it empty. This sort of perplexed me because other than the right side weak in reverse the unit performed fine. I filled the reservoir to the level for cold and performed the air purge. I pulled the bars used to disengage the drives, started the mower, and began performing the purge. Everything I had seen on this said the wheels would not turn when the drives were disengaged, but my tires turned. Not just a slow turn, but as if they were still connected. I thought I may have done something wrong.

Even after performing the purge routine several times the right side reverse is still very weak. Can someone tell me what I did wrong?

Sounds like you didn't fully disengage the drive. Try jacking up the mower & see if you can rotate the wheels by hand after you feel you have disengaged them. Bet you can't.

bullet bob said:

Sounds like you didn't fully disengage the drive. Try jacking up the mower & see if you can rotate the wheels by hand after you feel you have disengaged them. Bet you can't.

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I thought the same thing. That is why I checked it over and over again. These were pulled out fully to the notches. When jacked up and disengaged the wheels were still engaged.

I will try again. Maybe I can pull those out even further.

I had the same problem with my Gravely. Turns out I wasn't being 'manly' enough. Really rip on that thing!

bullet bob said:

Really rip on that thing!

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LOL. Will give it a try!

On some mowers you have to pull the release levers out and lock a pair of vice grips on them to make them release, Check the motion belt.

The shape of the release levers has an L-bend at the end to pull on. I was able to pry on it with a screwdriver and still nothing. In the meantime I noticed I have a charge pump cover leak. I just ordered the parts. I will tackle both when the parts arrive.

Don't tell anyone this, but I put a tow strap around each one & gave it a mighty tug. Piece of cake..........

bullet bob said:

Don't tell anyone this, but I put a tow strap around each one & gave it a mighty tug. Piece of cake..........

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Around the disengage levers?

When I pull mine out as far as I could by hand there is a notch on the bottom that keeps them extended. What bothers me is there is no resistance to pull out at all. All the way to the notch. When I try to pull further it is dead stop. So much so I am afraid of breaking something. When I go to fix the charge pump I want a closer look to the actual arm that disengages it.

I am horrible at descriptions. I thought to get a diagram (below) showing the "dump valve lever". The arrow points at the notch. When the lever is pulled out the notch catches on part of the frame I assume to lock it in the extended position. When the lever is in that position the tires cannot be moved by hand. I assume because they are not disengaged. The lever moves with no resistance between engaged and disengaged positions. My charge pump parts arrive late today. I will install them tomorrow and take a closer look at the dump lever system.

How many hours on meter if equipped? What year is mower? Have you ever changed the hydro oil and filters?
If you remove charge pump cover, you will have to drain most of the oil. There is an O-ring that seals the cover. Unless it is really leaking, I wouldn’t worry about it. Sounds like hydrostatic transaxle internal parts may be worn and causing weak reverse movement. You would not know unless you remove entire transaxle and open it up (big job).

Yes, around the disengage levers. However, I don't have the notches, just a slight 'release' when it goes that little extra. Good luck sir. Let us know what you find out!

SJMaye said:

Around the disengage levers?

When I pull mine out as far as I could by hand there is a notch on the bottom that keeps them extended. What bothers me is there is no resistance to pull out at all. All the way to the notch. When I try to pull further it is dead stop. So much so I am afraid of breaking something. When I go to fix the charge pump I want a closer look to the actual arm that disengages it.

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The parts arrived and I have them installed. To clarify- Like many ZTR mowers, mine has two hydrostatic drives. Both are connected to a single external reservoir that feeds them. I should have clarified that the leaking charge pump cover was on one drive and the other drive is the one with the weak reverse.

After installation I remove the fill level plug on the leaking drive, removed the fill level plug, refilled the reservoir and waited for the some to bleed out. After that I performed the air purge procedure several times. I never was able to pull the dump valve lever out further. I pulled it to the notch and did the air purge.

I am happy to report the leaking has stopped and both drives perform the same in reverse. Neither will set the woods on fire, but they are working about the same. Many thanks for your help!