ZD21 HST Tear-Down & Rebuild

[progun1]

So, I've read all of the posts on here regarding the ZD21 and it's various issues. My mower's serial number is 59933- just missing the #59999 mark and likely to have HST issues.

Upon getting the mower with no known history, I got it running and did a quick function check to see what worked and what did not in order to determine if the mower was worth my time. It runs and both HSTs operate, just the deck won't lift. I subsequently changed all of the filters, fluids and fuel line.

I took the screen out from the bottom of the transmission and noticed fine aluminum shavings as well as gray rubber? When I drained the right HST, 8-10oz of water drained out, followed by some hydraulic fluid and algae. The mower sat for some time. It's a 2004 with 303 hours (the hour meter is functioning).

My initial thought was to just run it until problems surfaced and then fix them as they come. However, I am now thinking that even though it's a bit above my knowledge and experience- I should remove and disassemble the transmission and HST's. I have all winter. I'm worried that if I continue to run it, I might really cause some issues. Whereas, if I take it apart- if for no other reason that making sure it's clean, I'll avoid anything catastrophic.

While I've never torn down an HST, I have tackled a few John Moses Browning contraptions. Hopefully they're not much more complicated.

 

[progun1]

Well, I figured out what the grey rubbery substance was- gasket. Whoever had the mower previously tore down the right HST. It also appears to be leaking around the aforementioned gasket. Given this shody gasket job and the heater hose used in lieu of fuel line, I'm a little dismayed. Although, I'm not quite sure how bad they really could've jacked it up in 300 hours.

 

[lugbolt]

replace the charge pump while you have it apart. at the very least pull it off and apart, inspect it very well.

 

[progun1]

replace the charge pump while you have it apart. at the very least pull it off and apart, inspect it very well.

I think I figured out what all of the problem was.

Going back to the beginning with the mower- along with the deck not moving and what I found draining the system- there was hydraulic fluid covering the right HST.

Naturally, this concerned me greatly, because why would there be hydraulic fluid all over the HST?! It must be from a terrible leak somewhere. So, I changed all of the filters and fluids and ran the machine for about 20-30 minutes. There were no major fluid leaks observed, just a little bit leaking around the gasket on the right axel case.

Upon thorough inspection, I noticed a few loose bolts on the axel case- this is what led me to believe it had been cracked before. After checking the tightness on all of the bolts, I noticed that the only loose bolts were the two that held the bracket for the hydraulic valve and those two places were where the hydraulic fluid was leaking from. Bingo!

I now believe that hydraulic fluid covering the right HST and leaking from the right axel case can all be traced back to whoever had it before me trying to fix the deck issue. It's all connected. They thought the deck not moving was a hydraulic issue- not the fact that the PTO shaft was frozen.

I sure hope that this is the case and I'm out of the woods.