Internal Tranny Mods, Swapping gear sets.
 

Someone here told me that 4th gear was not swappable because it directly coupled the input to output shaft.

According to www.howstuffworks.com and their article on manual transmissions, it appears that this is nto correct. 4th is just a 1:1 ratio that makes the RPMs the same.

Couldn't one just press the gears off the layshaft and output shaft.

Then you could get any of the Mazda trannies from to swap gear ratios from, providing that they have identical layshaft and output shaft diameters. (IE N/A RX-7's from 1978-1988)

I wanted to make a 4th and 5th gear to compensate for a 4.3-4.44 ratio differential.

The fourth gear in an Rx-7 tranny is directly coupled to the input shaft. Take one apart, if you have one availiable, and look at. There is technicialy no GEAR for fourth gear. I don't know how else to explain it unless you under stand how the interals work.

Ryan

Anyone got pictures of one taken apart?

I only have seen the diagrams at www.howstuffworks.com ... That's all I know about transmissions...

I forget if the Haynes or teh Shop manual have diagrams.. Need to check when I get home.

The only individually swappable gears are 5th gear, and Reverse.

All of the other gears on the countershaft are one piece - the gears cannot be slid off, they are part of the shaft.

oh oh, does this mean I could possibly swap 5th gear from a second gen, or someone with a lower ratio? 110km on the highway is about 3000 in 5th, I'd like something lower for highway cruising and gas mileage. What's possible?

Yes it's possible... Miata people do it all the time apparently. (They use the same tranny)

Yes it's possible... Miata people do it all the time apparently. (They use the same tranny)

You must live where it's flat. My main complaint is 5th gear is TOO tall and I end up leaving it in 4th on the highway... and Ohio ain't very hilly either, at least not where I drive. :)