There are many differences between the JDM and USDM transmissions on Honda b-series engines. Here are some of the things I discovered while rebuilding several transmissions.
2 years ago I bought a s80 case (USDM) when I rebuilt my y21 JDM transmission, because of cracks in the y21 housing.
Then after 1 year of use, a metal plate on the freeway hit my transmission and caused a hole.
The aluminum was brittle and filled with stress cracks in the housing, so when I TIG welded the hole, it caused issues.
I decided to go to the junk yard and get a s80 case from an integra. I found a 1995 3 door RS 5spd and pulled the transmission. (read about it here)
I did not know it at the time, but after I got home, I found it impossible to find a large oil cap.
I tried Honda and Acura dealers, and even used JDM engine suppliers, but no one had any for sale.
The USDM 1994-1995 Honda Del Sol VTEC model is the only USDM car with that oil cap. The part is discontinued and not available.
I needed a way to cap my new rebuild, so I tried to change the breather vent tube (oil fill hole) from the USDM s80 case to the JDM s80 case.
I have a b16 SIR2 that came with a y21 LSD transmission, but the case leaked and I replaced it with a more common s80 about 2 years ago when I rebuilt it.
I added carbon lined synchros, new bearings, new rubber, new gaskets, measured and replaced as need, full rebuild.
I was driving on the freeway about a year ago and a piece of plate steel was pulled up by the wind, and busted a hole in my s80 transmission case.
This is an article about how I got a replacement housing from the junk yard.
My car (1988 CRX HF) came stock with a Cable VSS (Vehicle speed sensor) on the transmission. The engine is a swap (b16a sir2, y21 transmission w/lsd) and was still using the cable VSS. After I installed the Integra cluster in the CRX, I needed to convert the car to Electric VSS.
I purchased a used transmission case for my car, because my case had a leak from a crack.
The new case came and I noticed damage from someone using a bolt too long in the front mount.