Topic: Need Help: R Tranny Basics (long)

[wrenchtech]

I hope this is easier for you all to read than it was for me to write.

In trying to figure out some issues for an engine swap with a Toyota "R" series transmission I realized that I don't fully understand how these transmissions (or any other manual transmission) really work. I was wondering how to change the first gear ratio to a lower ratio when I realized that I don't know exactly how this transmission works generally.

Just from looking at a factory shop manual I think I understand that there are three main shafts; the input shaft, the output shaft and the counter shaft. Power enters the transmission through the input shaft which has a gear that is always engaged with a gear on a second shaft, the counter shaft, which is below and parallel to the input and output shafts. The input and output shafts are in the same line and look kind of like one shaft when they are installed; in reality they work as separate pieces, each turning without direct connection to the other.  The power enters the transmission from the input shaft which has a fixed gear that turns another gear on the counter shaft that lies below it. The counter shaft has five gears that each engage gears on the output shaft that lie above it. I think the shifting action all takes place on the output shaft where forks mounted on shafts push the output gears in and out of contact with the gears on the counter shaft. I think all the gears on the counter shaft are a fixed part of the counter shaft. In other words if a gear on the counter shaft was damaged you'd have to replace the whole unit.

I don't know exactly how the selecting of the gears works though. I know that syncronizers fit between the gears and engage them first to spin the selected gear up to the same speed as the matching gear on the countershaft so that they engage without grinding, but I don't really understand how that works actually, except that I know that something is forced to slide back and forth (on the output shaft?) by the forks to force the gears in and out of engagement.

So to answer my main question; when you want to change the first gear ratio do you have to replace the whole counter shaft and and a gear on the output shaft?

Secondly, am I pretty close on the basic operation? I wish I had  schematics of the power flow through each gear.

I'm attaching a drawing of what I think the typical power flow is
like.

Matt

[Marlin]

Well, it a little long winded but you did a good job

As the 1/2 shift hub is moved by the fork to enguage into the drive teeth on the side of the 1st gear, it has to move across a brass syncrow ring which is spinning the same speed as the 1/2 hub thanks to 3 evenly spaced syncrow keys.The 1st gear also has a male 30 degree hub that matches the 30 degree female taper found on the inner side of the syncrow ring. This system works very good by slowing down, or speeding up the hub or gear before the teeth enguage.
 
There are two ways to get a lower gear ratio--
1. Put fewer teeth on constant run teeth of the input gear, (this would make it smaller), and more teeth on the front constant run teeth of the countershaft. These added teeth would make the counstant run gear larger to keep the same case centers. This would underdrive the countershaft and make all gear ratios on the shaft turn slower.
2. Put fewer teeth on the countershaft 1st gear, and more teeth on the matching 1th mainshaft gear.

Remember by making a gear smaller,there are fewer teeth enguaged and as a result, weaker.

Hope this helps, and you are still awake--

Marlin

[84runner]

That was very educational both of you.  And you did a good job explaing your understanding of the manaul transmission Matt.