Z100's and Z400's are hydrogear, ZG200's, 300's, ZD's are Kubota, Z700's are Parker units. That is the major models that I deal with. F series are all Kubota. Older G series were mostly Kubota. GR? JUNK. Dunno who makes that pile of trash transmission, and don't care. I have one...bad transmission...was given to me. Havent' decided what to do with it, thinking about BURNING it, so that nobody else has to endure the infamous GR2100/2110/2120 curse! some of the older T series used tuff-torq, I'm thinking maybe the T1460/T1560--but I may be wrong. They were 10x better transaxles than the JD LX100 series, and completely different too, in every aspect. I tried to put a LX172 transaxle into a T1460 chassis. Could've been done but would've been a TON of work (reengineering the belt drive, shift linkages, brake links, modify fender for shifter, etc etc). Not worth the trouble when there's a few thousand other ones out there laying in people's yards and barns rotting away.
JD LX100's were tuff-torq. They were noisy. No charge pump to speak of. Most JD FSR's said don't even change fluid in them, if it's not leaking, leave it alone and run it-said they'd last the life of the mower when used normally. They were right. Most of the time the hood shattered, then owner found out how much that PLASTIC hood cost, then the mower got replaced and/or scrapped. Thus at least in this area there are TONS of LX100 series mowers laying around. Just look behind houses for green/yellow and no hood. LX176, 178, 186, and 188 were all mostly the same with engine and deck differences. The LX172, 173 were 5 speed gear drive. They were all pretty good mowers but getting parts for them is getting tough due to their age. I had a beautiful VERY low (under 10 hour) LX188 given to me because the owner said it wouldn't move. Great, another project. Nope....the ALUMINUM HST pulley's splines were GONE (in about 10 hours' use???). JD updated it with a different pulley which lasted the rest of the time I had it. Aside from that issue and the asininely designed BRITTLE hood that shattered while MOWING (on flat smooth ground nonetheless), it was a pretty good mower. I put that $700 hood on it and cleaned it up real good, then sold it for $1000. Came out ok on it. People will still pay good money for 'em as long as the hood's not broken, and those are getting very rare. If no hood and other problems? Even just no hood and working mechanically? Worthless. Or worth very little anyway. People know what those hoods cost and there are a grand total of zero good hoods on the used market worldwide (at least that I know of). That is the problem with all of them (hood).
I sold a few hundred of the LX100's back in the 1990's and very early 2000's. Worked on them for other dealers who didn't want to as well...so I had PLENTY of work. There was a big recall on the key switches, they liked to catch fire as I recall. HST pulleys failed often, were updated with new style. Old ones NLA. Have to make sure the clutch is adjusted properly (even on HST models)...the belt drive is attached to the brake, so when the park brake is set, belt tension is removed. But the downside to that design is that when/if you get off the mower, you have the brake set, and engine running....the belt is constantly slipping a little, and it gets hot.
BUT...what I do like about the LX100's, specifically the 178 and 188, is the water cooled kawasaki engine. Adjust the valves and they are super quiet running and VERY smooth running. My favorite is the 178 with the smaller V-twin. Barely hear it running at idle speed in neutral. Also on the 178, they could be had with 3 different mower decks, 38" (run of the mill), a 44" Piranha, and a 48". The piranha deck had 6 blades and cut wonderfully but it liked to suck up a lot of power and was tough keeping everything working; the plastic deflector under the deck was required for a good cut but most in this area ripped it out by hanging a rock or stump in the first 1 minute of use. Those that didn't....enjoyed a SUPERB cut quality as long as the deck was leveled before use. The 188 I had, I got it with a 48" and it was slightly too big for the graveyard I was cutting, and I found a guy who bought a brand new 345 with a Piranha and he hated the deck. We did a straight trade and he got the 48" which worked for his needs and I got a brand new 44" that made the cemetery board extremely happy with the cut quality.