Automatic Overriding Trans

[BadBillyB]

Since a couple of you asked, I will try and explain this mod. I dont know your level of expertise but first you must fully understand how the trans shifts from gear to gear. On a stock trans, when you go from 1st to 2nd, two shift forks are put into motion. One takes it out of 1st and another puts it into 2nd. This is done simultaneously...... It also requires that the load be taken off the gear that your coming out of (letting off throttle, using clutch, killing ignition etc) .....Now when you have a 1-2 auto, when you shift into 2nd gear, only one shift fork is put into motion. The fork that put it into 1st stays put. This is done by modifying the shift drum. At this point you are in two gears at the same time. Now when 2nd gear "overruns" 1st gear, the engagement dogs on 1st gear move to the "braking" side of the receiver slot......It MUST NOT be allowed to cause any engagement whatsoever or the cases will explode....So what you do is cut a ramp on the braking side of the dog and also round off the slot in the matching receiver gear so it "spits" the gear out when it hits this ramp.....You also spring load the shift fork in the same direction that the gear is getting spit out to....This keeps the gear from bending the fork as the fork is designed to move the gear not the other way around. So, if your following this you can see that the only thing keeping the trans in 1st gear for that split second after engaging 2nd gear, is the undercut or backcut of the gear........So here are the steps

Send trans out and have a professional "race cut" done to it
Grind away the section of the shift drum that causes the fork to pull it
out of 1st when you shift into 2nd
Cut a 45 degree ramp on the braking side of the 1st gear engagement
dog. Narrow this ramp by cutting the sides down, so as only the
center of the ramp contacts the rounded off receiver slot. These
ramps MUST be indexed where they all contact at the same time.
I made some fixtures, with indexing stops, that bolt to the table of
my Makita chop saw....primitive eh
Round off the receiver slots sharp corner making it more flat than round.
You dont have to ramp this part, simply round it off, keeping in mind
that indexing is important. All the dogs must hit the ramp at the
same time or the gear will try and cock on the shaft
Spring load the shift fork by placing a spring on the forks shaft between
the fork and the case. Pretty sure I used rocker shaft springs off
a 4v GS 1100.
Now test your modified gears by placing them on the gear shaft. Hold the
shaft in a vertical position and rotate the bottom or receiver gear
with your hand. The other gear should smoothly and without any
binding, lift right up. If it does not, than fix the indexing issue by
marking dogs with black magic marker and find out which ones are
hitting first. When you get it just right, it will be smooth as glass.

2nd to 3rd is done exactly the same way
You will NOT be able to do ANY engine braking in 1st gear after this mod

BadBillyB

 

[Richie]

thanks for the information Billy...richie

 

[massakins]

Billy, that is one of the best explanations I've read about a technical topic. Well done. Thanks for sharing the information.

 

[BadBillyB]

Your welcome. I hope I explained it good enough for all to understand. Would have been much easier if I showed you in person or with good pics. This is one area the Suzuki ruled over the late 70's early 80's Kawasaki's........The Kawasaki trans uses the same gear for 1st and 2nd gear. In other words in order to do a 1-2 auto on a Kaw, you had to split one gear down the middle, move 1/2 of it one way for 1st and the other 1/2 of it to shift 2nd.......Imagine the surprise on the face of the shift fork...They were always breaking...........The Suzuki trans on the other hand, had no gear that had to be moved twice, in sequence, to obtain the next gear..........BadBillyB

 

[scotty]

is that usable on the street??? And thanks for the explanation.