ZD21 Hydro Rebuild

[fatjay]

So my new to me mower needs a bit of work. The left side hydro is acting up, don't go into reverse, and sometimes doesn't go forward. I knew that when I bought it, the guy advertised it as engine only, but I took the whole thing.

This issue is caused by the hydro sucking air, which is most common when mowing on hills, because the reservoir isn't large enough. I'll add the kit (P/N: K3111-98600) which adds a reservoir tank for $250 when I'm done.

Last night I started the disassembly process. Took the fender and gas tank off, so I can get to the rear axle. There's 6-8 bolts holding the axle to the frame, and a couple more holding the axle to the hydro motor, so they should be pretty easy. Hopefully when I pull the hydro the cause is aparent, because if not I'll be pulling the right side to compare.

So far this only took about 45 minutes, and one 13mm socket and one 13mm box wrench. Litterally every bolt i've come across so far is 13mm.

 

[D2Cat]

I'd be cleaning that up before I removed many more parts! You need that to be "surgery room clean".

 

[fatjay]

Yeah I was going to put the wheel back on and wheel it out and wash it up, but it doesn't exactly like to free wheel. Is there a hydro release somewhere so it can move freely?

Edit: I just got off the phone with a service tech, there is NOT a "neutral" position. if you need to tow it for any reason, it should be done extremely slow, as to not burn out the clutches.

 

[fatjay]

Got it all off and the hydro split. It seems like there was serious cavitation going on.

Notice one is worn more than the other:

And that is a pretty big groove.

 

[Dr Honda]

Cool project.

I haven't ever cracked open one of those tranys... I'm assuming the cage, and plate should be flat?

 

[fatjay]

The plate should be completely smooth to the touch. That's what happens when you suck air, the cylinder with the pistons is spinning against that surface, and designed to be completely encased in hydraulic fluid. No hydraulic fluid, no lubrication.

I have a spare good cylinder, since the one on hte left is damaged and can't be reused, but I need that plate, and I can't find a part number anywhere.

 

[RCW]

Jay - thanks for posting this.

I've never had anything like that apart, and don't really get how they work.

I used to do a lot with water wells, and saw a similar thing with impellors on bigger pumps due to cavitation. Saw an 8-stage vertical turbine with 8" (?) impellors busted down to 5 or 6" due to cavitation. Damn things looked lost inside the bowls!

In similar fashion, the grooves are created in your hyrdo....

Thanks again, helps my understanding of how these things work.

Trust me, still don't get it, but my understanding gets better all the time...the beauty of OTT!

 

[fatjay]

It really wasn't difficult to get to this level, less than 2 hours and nothing was very difficult. All the bolts were easy to get to, just a bit dirty. Gender came off with 4 bolts, gas tank 5, rear axle was 4 on the trans, 4 on the frame. Then the hydro itself was another 4. Splitting the hydro was 8 alien heads and fairly simple. I'll post more detailed pictures when I put it back together. My hands were pretty greasy at the time of disassembly.

 

[RCW]

It really wasn't difficult to get to this level, less than 2 hours and nothing was very difficult.

That's cool. Always nice when it's relatively easy to get into the "belly of the beast."

Like I said, my interest lies more with how those darn things work.

Hell - I had a more difficult time getting at the wiper motor/linkage on my wife's Chevy Equinox!

Thanks again.

 

[Dr Honda]

The plate should be completely smooth to the touch. ................

I have a spare good cylinder, since the one on hte left is damaged and can't be reused, but I need that plate, and I can't find a part number anywhere.

Is it steel or alumium? Could it be welded and resurfaced?

OR......

if it's thick enough... just have it resurfaced without welding it up.

Just some thoughts.


Oh.... one more....

Could you have a stainless sheet cut, and just lay it over it? (or bond it to the plate) I've seen that done to large gear pumps to save the endplates.

 

[Dr Honda]

I was just looking close at the pics again... you can really see the wear on that one drum. The scallops on the outer edge are significantly smaller/shallower than the other.

 

[fatjay]

Yeah, they're a lot shallower than the one on the right. It was tricky to see at first, I wasn't sure if there was any damage to begin with on that, or just the plate. I have a 3rd drum though, which I could compare it to.

The housing is steel. I could weld/refinish it, or have a machine shop do it, but I'm not crazy about having to do it again in a few machine-hours. If it's not done right, it'll last 20 minutes. I tried to take a shortcut once on a lifter vs cam lobe on my bike, it lasted 1/4 mile.

 

[fatjay]

Good news! Someone is able to get just the transmission cover! Bad news, it's $600. Still a lot easier than $1200 for a new transmission. I just need to sit in my garage and make sure that it's all that I need.

 

[100 td]

Personally, before ordering any parts, I would pull the other drive apart as well and see what it's like. If things aren't perfect in it, you may be able to make one out of two, and then order one complete hydro. Buying a new cover then a new cylinder assembly and bits will push the price out and a complete hydro will work out cheaper/better in the long run. YMMV. Good luck!

 

[fatjay]

That's a pretty good idea. I hadn't thought of that, and I wish you hadn't suggested it. I don't think I'll get a bulk order discount. The drums aren't available easily either. However there's not that much that can fail, the plate and the barrels are really only the metal on metal without rollers/bearings.

The down side is that the wife may be tollerant of nickle and diming vs up front cost. Less likely to notice a few smaller charges than one big one.

 

[Dr Honda]

Good news! Someone is able to get just the transmission cover! Bad news, it's $600. Still a lot easier than $1200 for a new transmission. I just need to sit in my garage and make sure that it's all that I need.[/QUO0TE]

Hummm...........

Don't know. $600 for the plate. Still need some gaskets, maybe a few seals, bearings... and have to replace that drum. (I know you said you have it, but there's a "value" with it)

Personally, if I was going to keep it... I would just pay the $1200 for the new trans.

 

[fatjay]

The bearings are in good shape, I haven't been able to find any defects at all with other parts. The guy included a spare drum/case/pistons/springs from when he rebuilt it last time when the swash plate went bad. Total is 544 for plate + $8 for the gasket. There's amazingly nothing else, they designed it with reusable o-rings, which are cheap to begin with.

I'm going to clean it up better and see if I find any more defects. I want everything to sparkle before I put it back together.

 

[fatjay]

Ordered the new plate and gasket as well as a new filter. Does anyone know if it's safe to use assembly lube in the hydro system? Also is it the same oil as my yellow buckets of hydraulic oil from tractor supply?

 

[Dr Honda]

If that oil was just staying the "Gear Box"... I would say yes. But since it needs to hold pressure in the seals of the rams in the system... I wouldn't use it. I would personally put a small bucket of your hydro fluid next to the bench, and just dip the parts as it goes together. Besides... as it starts the first time... it will be a in a no-load situation, and the oil will get pumped in quick.

 

[fatjay]

You mean the assembly lube? Or putting hydro fluid from TSC in the hydraulic system. I'm assuming it's hydraulic fluid in there, but I don't know for sure.