The top left port is facing the inside at the top on the transaxle and needs an allen wrench to remove for venting. There is one on the right transaxle also(same location) and it must be removed also. Just did mine, requires right at 5 quarts 20W50 motor oil( I used Castrol GTX). You can make access to the vent plugs easier by removing the trans brake levers(pop off the C clip). There is a write up for the procedure online. There is no drain plug, units drains through the filter on removal.
Dealer wanted $53 for 2 new filters. I walked out laughing. Got online and found 2 new factory Hydro Gear 52114 filters for $17 shipped.
Here is a writeup I found that helped but not the same mower. My operators manual says to service the transaxles after the first year or 75 hrs, whichever is first.
NOTE- Hydro-Gear says the zt-2800 needs a fluid change after the first 75-100 hours and then every 400 hours. It suggests a 20w-50, so I used a 20w-50 synthetic motor oil. All together, 4.5 quarts went in. Also, instead of using (2) JD oil filters, I used (2) purlator oil filters.
*This is for the 2011 z425 models that does NOT have the engine turned in the frame.
**Do all at your own risk! Use this post as assistance. I am not a professional mechanic. Even though it worked great.
1. Drive the z425 around a bit to warm up the fluid in the transaxles. Park.
2. Jack up the back of the z425 so that the tires are about 1-2 inches off the ground. I put one single jack in the middle of the back part of the frame. You want the rear wheels to be about to spin off the ground.
3. Take off the reservoir cap, and then go under each wheel hydro and take the plastic guards off each oil filter. 3 bolts holds it on. Also, behind each wheel is a rod to allow the hydro to be in neutral. Pull each rod towards you so that both wheels are in neutral. (you'll need this later for the purging)
4. Place two oil pans under each filter, remove filter, and let all the fluid drain from the system. About 15 minutes.
5. After drainage, clean around each filter port, fill new filters will a little oil, and put on (2) new oil filters. Put guards back on if you want.
6. Now, here is what's important. You can't just pour new oil into the reservoir. You must unscrew (2) allen plugs. One on each side. Each is on the side, very close to where the hoses connect to the hydros. Use a 1/4" allen wrench. (it helps to take out the battery.. they are in tight as well). This will allow the new oil to drain in quickly and breathe as you fill. Also, clean each allen plug and put some anti-seize on them.
7. With both plugs out and new filters on, start pouring new oil into reservoir. Each transaxle takes about 2 quarts. You will know when each hydro is filled because oil will start to pour out of the exposed hole from the allen plug.
8. After you put in about 2 quarts, start watching the allen plug hole on the left side hydro (one right under the reservoir). This one will fill first. As soon as you see oil coming out of the hole, quickly screw the plug back in.
9. Pour in another 2 quarts, and you'll see oil start to come out of the other allen plug hole on the other side. Put that allen plug back in. Tighten each plug to about 180 INCH pounds.
10. With both plugs in, I poured about 1/4-1/2 of a 5th quart into the reservoir. Keep the reservoir level to COLD FILL LEVEL, and keep the reservoir cap off for purge procedures.
11. Now you have to purge the system. Make sure the neutral rods are pulled towards you (remember from step 3 - the little rods behind each wheel).
12. With the z425 still jacked up, wheels off ground, get on and start up. Take the parking brake off and slowly move the throttle levers forward and reverse about 5-6 times. The tires shouldn't move.
13. Keep the tractor running, get off, and push the neutral rods back in to allow the wheels to move.
14. Get back on the tractor, take the parking brake off, and move the levers again. Forward, reverse, forward, reverse, forward, reverse. Again, again, and again for about 5-10 minutes. The wheels will spin. Also, as you do this, look behind you into the reservoir. You'll see air bubbles come up from the hoses. This is getting the air out of the system.
15. After about 5-10 minutes of purging, drive the z425 around. When I drove mine, there was no more squeal while driving and turning. I was very happy.
16. Keep an eye on the reservoir level for the next couple of cuts to make sure all air is out of the system.
*Hope this helps someone. I was very pleased with my results.
**Download the Hydro-Gear zt-2800 manual because it'll have pictures.
Hopefully I remembered everything. If you have any questions, please post.