I had a failure in a Miata 5 speed so I pulled it apart to diagnose it. This obviously required learning how the whole thing works. After doing this, I thought this might be beneficial to some of you that haven't ever dug in to seen how they tick.

I am not covering shift rods etc in this, but really...once you understand which gear sets are to be engaged for a given gear, you can pretty easily figure that part out. At a minimum this should help you accurately identify the component that failed.

The first image labels the major components of the gear set.

- Primary drive gear - this gear transfers power from input shaft to the counter shaft (in all gears except 4th)
- Input shaft - connected to the clutch/engine
- Counter shaft - pretty much what makes a manual transmission possible
- Output shaft - connected to the driveshaft/rear axle

Fourth gear is the odd man out (in a 5 speed). Essentially the input shaft and output shaft act as one unit and the counter shaft/gears are free spinning and along for the ride providing a 1:1 ratio.

In all other gears the input shaft rotation is transferred to the counter shaft and then one of the gear sets(1st, 2nd, 3rd, 5th, reverse) is engaged to transfer power back to the output shaft.




In this image I have outlined the path that the power takes based on gear selection.

Green 1st
Blue 2nd
Purple 3rd
Orange 4th
Red 5th

 

Each gear is engaged using a sleeve that I believe is referred to as a clutch hub (If anyone has better terminology, let me know). In these pictures, all clutch hubs are in their neutral position with no gear selected. They are moved using the shift forks.

The clutch hub is in two parts an inner portion that is fixed to the shaft and an outer sleeve that slides side to side. When the sleeve slides to the side, it engages the gear next to it. When this sleeve slides over it initially engages with the synchros(brass colored image) and eventually wears them out. Once engaged with the synchros, ideally the speed of the shaft/sleeve is close to that of the gear it is mating with and the sleeve slides all the way onto the mating splines of the gear.

This diagram shows the direction they would move for each gear.

 

The next step would be to show shift forks and rods. Unfortunately, I don't have a trans that is complete enough to show much else. If you see an error or have alternative terminology, let me know and I can revise. Hopefully this is useful to someone.

Most generic manual transmission info is well documented. I was just hoping to make a quick reference for Miata 5 speed specific operation.

 

Awesome!!

 

Great work on this, thanks for providing a learning resource!

 

Figured this would be appropriate here.


Love these old educational videos - there's a good one on fluid couplings, planetary gears, and differentials on youtube as well.

 

Agreed, I love posts/articles like this.

 

Wow, that first gear behind the input shaft is really chewed up!