How does the aftermarket close 1st gear work in the D transmission when they only replace the counter shaft gear and the main shaft gear is fixed in diameter and tooth count? At least that's how I am understanding it. It seems like with the fixed spacing of the two shafts in the case, that would be impossible or have to run with a lot of slop, but yet it works for a lot of people. So maybe someone knowledgeable can break it down for me? The reason I asked is the 1970's Civic transmission has a one piece main shaft for all gears except 5th. There was a company in Australia in the early 80s that made a close ratio 4 speed box swapping factory gears with a few custom made sets, but all info is just rumor at this point. I figure if I understood the way they make it work on a D series transmission, then I can better check into custom gears as the stock 70's gearbox spacing is so bad for anything other than around town use.

 

Responded to you over on DSO, pasting my response here for anyone that stumbles upon this in the future.

When only changing half a gear, there is only so much room the ratio can be changed. To do this with a factory gear is very expensive as it requires new tooling for each specific gear and you still have a gear that isn't stronger than stock (as half of it is still stock).

One off custom gears are available and affordable, contact me for more info.

 

Thanks for the info. After going back and forth, I have decided to just use the 40 year old mugen dog box. Its lasted over 40 years so its proven and still in decent shape. If it does have a problem, I know where to send it!

 

That mugen box would probably pay for your retirement.

 

Maybe, the only one like it that I know of is in the Honda museum in Japan in the Yamato Civic. There have been a few people inquire about it, but they are cheapos mostly hoping to steal it. Even the shift pattern on the box was changed from honda's. Very special history.