# Gravely ZT 52 HD trans problem???



## Gundog

I bought this ZT in 2012 new and it has worked OK until today the left side has lost most of it forward or rear motion and sounds like the pump is making noise. I have never worked on one of these any suggestions. I worked as an equipment mechanic years ago but no knowledge on these units should I tear into it I see I can buy a new unit for $445 it is a ZT-3100 left side transaxle/drive unit. I will add I checked the belts and hydraulic fluid level they are both OK.

Thanks Mike


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## RC Wells

Not sure of your question, but these are homeowner grade hydro transmissions and are generally considered disposable when they fail.


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## Gundog

RC Wells said:


> Not sure of your question, but these are homeowner grade hydro transmissions and are generally considered disposable when they fail.


This one is called a commercial model but that maybe more about marketing. I paid about $6K for it with a power bagger that is crap in 2012. This was supposed to be better than the homeowner model and if I did not have so much invested in it I would get rid of it.


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## RC Wells

Marketing is an interesting animal. Gravely with this transmission is a decent machine for modest mowing jobs, but like everyone in the field they have price point units and dealers that push a sale without a good understanding of the buyer's intended use (or even a good grasp of the product itself).

For an average person to get 5 years use from one is about the expected life of that transmission. This is mostly true of every manufacturer's entry commercial units, so they build them to sell. 

Hydro-Gear calls the ZT-3100 an entry level commercial unit. But it lacks the all important shock valves that keep the operator from chewing up the drive motor. It is found in machines intended for very light commercial use on small lawns, and homeowner units for larger lawns that are used once every week or two.

In the Hydro-Gear zero turn transmissions the ZT-3200 is the lowest cost of their commercial series transmissions that actually contain shock valves to keep from knocking the drive unit out from frequent use. That unit should directly interchange with the ZT-3100, is about 20% higher priced, and when properly maintained has a considerable useful life.

You may wish to contact Hydro-Gear and see if they will rebuild your unit at an affordable price. The issue with most commercial mower repair shops is the labor to completely disassemble and clean all the passages and valves that get contaminated with wear particles, obtain the replacement parts, then reassemble, pressure test, and tune the steering valve linkage so the finished mower does not go drifting one direction or another is cost prohibitive. For the owner to tackle the job without the necessary tools would be daunting to say the least.


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## Gundog

Yes this one has the ZT-3100 in it. The dealer thought it could be the filter should I try a new filter the oil seemed pretty clean or would this be a waist of a new filter and oil? This unit has 212 hours on it.

I am not real happy with this mower the power bagger did not work well and now has bearing issues. Our land is not level and here in the NorthWest it is wet so it does not work well trying to bag. The wet ground also gets torn up by the zero turn drive system. I have been using it without the bagger lately it actually mows the yard good except for tearing up the ground in the spring and late fall when the ground is wet. I think when I get it all fixed back up I am going to try and sell it on CL and buy a garden tractor riding mower I am thinking that style maybe better on the ground. I mow about 1.5 - 2 acres with this machine.

I mow my pasture with a brush hog on my Kubota. I thought about buying a finish mower for the Kubota but I mow around trees and other obstacles that I can't get close to plus it has tractor tires on it rather than turf tires so it would tear up the lawn.


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## RC Wells

The oil and filter on those transmissions should be changed every 100 hours, a filter is an inexpensive option to see if it solves the problem.

I am in the middle of the Willamette Valley in Oregon so we are always wet from October through June. The lawns have to be mowed pretty much year around here. I use a four wheel drive four wheel steer John Deere X745 diesel with the Deere blower and bagger. The bearings in the bagger have to be changed every two years because of the wet conditions.

The tractor does not tear up the wet lawn, but I suspect when it is due for replacement I will go with a Japanese built Kubota simply because all the small diesel JD tractors are from China with a Japanese Yanmar engine (good engine, but the rest is suspect).


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## Gundog

I changed the filters in both sides do they have a method for bleeding the air out?


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## RC Wells

Work the steering/drive levers with the engine running and they clear automatically. It is clear as soon as the wheels drive.


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## Gundog

It took quite a while to get the air worked out. The right side works good the left side did not change so I will take that side out and tear into it. If I can figure out what is wrong with it I will look for parts if not I will replace that unit.

Thanks for the help Mike


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## Gundog

I pulled the unit out and found some broken springs inside the piston motor block and the center section was galled by the broken spring. The oil and parts were clean with no burnt oil. I do not think this was a dirty oil issue just a part failure. I will call tomorrow for part prices.

Mike


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## Gundog

I got the transmission tore down and found a spring failure in one of the motor piston assemblies. The piece of spring destroyed the center section housing and the pump piston block as well as the motor piston block. Total for parts to fix is a little over $425. The transmission I found on eBay was not the right part number for my unit the replacement unit for mine on eBay is $837 so I ordered the parts they should be here by next week. I do not believe this was an oil related issue the oil was clean and had no burnt smell at all. The oil on this unit was the same as the oil in the other side that was still working properly. For the record the ZT-3100 does have shock valves in it. 

After I get this whole thing back together and working properly I think I will sell it and replace the unit with a garden tractor type mower.

The first picture shows the side case removed.

The second picture shows the surface of the center section where the motor piston block mates with the housing you can see the galling from the piece of spring.

The third picture shows the center section where the pump piston block mates with the center section it was the worse condition funny thing is it was a broken spring in the motor piston block. The gear pump shows no damage but for $35 I decided to replace the gear pump also. 

The fourth picture shows the broken spring pieces there were some smaller pieces that are not in the picture.
The fifth picture shows the two piston blocks where they mate with the center section the larger block on the left is the motor piston block and the one on the right is the pump piston block.

The most expensive piece was the center section but it comes with new shock valves as a whole assembly it was almost $200.


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## Gundog

I got it all back together and tested it today and it works better than I think it ever did from new. Makes me wonder if it did not have an issue from the factory and just got worse to the point it quit.


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## RC Wells

Post the part number for the section with the shock valves. Being stonewalled by Hydro-Gear. Thanks.


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## Gundog

Here is a you tube video from HG that gives the difference between the ZT-3100 & ZT-2800 it says all 3100 models have the shock valves and some of the 2800 models have the shock valves but not all.

I was able to download a very good service manual for free from HG but I had to ask them for my particular model number to get the right parts schematic. The service manual does not list the actual part numbers just the schematic numbers once I had the part numbers I shopped ebay for parts but no one had the center section in stock and it had to be ordered.

[ame]https://www.youtube.com/watch?v=2dGYFzTAl70[/ame]


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## Gundog

RC Wells said:


> Post the part number for the section with the shock valves. Being stonewalled by Hydro-Gear. Thanks.


 I can post the part numbers but you need your actual serial number to order parts because even though they are 3100 models the center section maybe different at least that is what they told me.

71563 center section 195.12
71579 $61.40 ebay 272046820630
70723 $79.99 ebay 172490369530
72274 charge pump $39.99


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## RC Wells

Thanks, you paid less for the center section complete with shock valves for less than they are trying to charge for the shock valve kit alone.


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## Gundog

The one thing I did not list was the seal kit they left it off my order and I had to call back and order that. The seal kit is what pushed it over the $400 mark. Using the manual they have online this was fairly simple to rebuild but I was an equipment mechanic in my younger days and I have a very well tooled shop. It takes a special puller to pull the hub off the axle and I did not have one but I was able to press it off with a hydraulic press my hub had 5 lugs so my standard 2 & 3 jaw pullers did not work. 

I would not recommend this rebuild to the average joe unless they have done a fair amount of this type work.

I ordered everything from Parts Monster on ebay but called and ordered over the phone because no one listed the center section on ebay. Their regular business name is Woodland Equipment they are in MI.


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## RC Wells

Good to learn something new. Pulled a ZT-3100 apart to take a look, found what is called their shock valve system. Diaphragms on springs, not the same style with springs, movable slug, and orifice flow control used on the heavier units. 

My guys were very worried I would make them start rebuilding the 3100's, but not cost effective at shop labor rates. 

Going to leave that to talented homeowners like you. But, have printed this entire post and made copies for the folks that have the same issue and are willing to tackle the job.

Good post, thanks.


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## Gundog

RC Wells said:


> Good to learn something new. Pulled a ZT-3100 apart to take a look, found what is called their shock valve system. Diaphragms on springs, not the same style with springs, movable slug, and orifice flow control used on the heavier units.
> 
> My guys were very worried I would make them start rebuilding the 3100's, but not cost effective at shop labor rates.
> 
> Going to leave that to talented homeowners like you. But, have printed this entire post and made copies for the folks that have the same issue and are willing to tackle the job.
> 
> Good post, thanks.


I agree if I had to pay labor with what the parts cost it would not have made sense to fix it. I found a place that I could have bought a new unit for around $780 had my parts list reached $500 I would have just replaced it. I originally found a new unit for $445 but it was not a direct replacement for mine so I had to pass. I am not sure what the differences where probably mounting or axle length who knows.

I figure if I had taken it in to be repaired they would have billed me $1k for parts and $500 for labor or more. I would have had a new unit but at a much higher price.


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