Hi,

I need some help and info about modifying the shift drum in order skip 1st gear and have a pattern which goes from N-2-3 etc. Pictures are also welcomed.

Is modifying the shift drum a good thing ? or any other recommendations.

Thx.

Kev

Go take a look at a shift drum and mechanism and it should be pretty obvious how it works.

Why skip first and go to 2 and 3 when you can just change your final gearing.. and be N-1-2..

In any event, modifying a stock drum might be pretty tough. You'll likely have to cut a new one on a 4-axis CNC. I believe I even did a drum design up in CAD for a F4i that would be N-1-2-3-4, though never made it. The toughest part is figuring out the alignment of the dowel pin on the side of the thing for the actual "star" that the spring-loaded follower rides in.

And in retrospect, I'd rather have 1-N-2-3-4.

If you are modifying a drum to prevent shifting into first all you need to do is prevent the forks from traveling any further in their "tracks" in the drum.

Currently the tracks will wrap almost all the way around with positive stops before 1st, and after 6th. You just need to add a positive stop in the track between neutral and 1st. Just degrease and weld it up.

I'll try and get a picture later this week.

thx for the advice exFSAE and ibanez player.

Thx in advance for the picture ibanezplayer.

email- phenixx3@gmail.com

Rolled our shift barrel in ink to make the imprint, the left is the OEM, the right is our modified pattern to obtain a N-1-2-3-4 pattern.

You'll notice we didn't use the OEM 1-2-3-4, if I remember correctly, our 1-2-3-4 corresonded to the OEM 1-2-4-5. Unused gears were ground down to reduce rotating mass.



Here is a picture of the manufactured against the OEM.



Cheers,
Fred

We had to have the shifter drum acid dipped to achieve an acceptable weld.

@ Fred G: Methinks that shift pattern should wind up in the shared CAD library if it isn't there already. That's some excellent information, and a very clever capture method. Kudos for making the new drum from plastic; how well did it work?

Why do you guys need to machine a new shift drum? We moved neutral to between 5 and 6 with a modified shift star. Took all of 20 minutes to machine.

Yes, it's relativley easy to "add" neutrals by modifying the shift star, but that wouldn't prevent you from shifting into a first gear that had been removed.

Also rolling the drum in the ink is an ingenious method!

And +1 for adding to the shared CAD library

Unless I am looking at something wrong it looks like your modified pattern actually corresponds to 1-2-3-5 OEM positions.

Very ingenious method to capture the pattern!

We did something similar to this with an air shifted FSAE car back in 98. We removed 1st gear, ground the the original neutral switch bump off of the shift drum and added a new neutral bump in at the new first gear position (used to be second gear) and instead of turning on a neutral light, the new 'neutral bump' actuated a relay when you downshifted to first gear that wouldn't alloy you to down shift anymore. To down shift into neutral you'd have to actuate a switch which put you in 'Neutral Mode', which reversed the relay so the downshift paddle would now allow the actuator to downshift again putting you in neutral. Additionaly in 'Neutral mode' the upshift paddle wouldn't work. Basically the car could now sit running with a 'Neutral Mode' light on and you couldn't accidentally put the car in gear by bumping the upshift paddle, also preventing you from accidentally driving around in neutral mode...

Dave Cook
www.paradigmmotorsports.com

Last year we ran N-2-3-4, machine and removed 1-5-6 from the trans. All we did to the drum to was weld stop in the tracks to prevent the forks from moving into the undesired positions. Worked Great.

Brian,

I think you're right.

The pattern is out of a 05 CBR RR engine if I'm not mistaken.

Cheers,
Fred

quote:

Originally posted by Brian Barnhill:
Unless I am looking at something wrong it looks like your modified pattern actually corresponds to 1-2-3-5 OEM positions.

Very ingenious method to capture the pattern!

We achieved a N-2-3-4-... by closing the first-gear-"pocket" of the shift star in a way that the shift drum rotates back to neutral if you downshift from 2nd.

Here is a drum we came up with , got the prototype made which worked well . We carried out a hardness test on the stock piece and got it to be 46-48RC . Material for the final piece is yet to be finalized .



Inder Singh Sehra
Orion Racing India
Powertrain 2010

my only qualm with using first gear position as a neutral is having to run a large rear sproket. This is what we used to do, then welded up the path for 1st and neutral we machined our own on a mill. Not to difficult if you look at the part and think a little.