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Old 04-05-2007, 05:20 PM   #1
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Trans gears.

I asked my uncle about custom cut gears yesterday, and he didn't seem too enthusiastic. Pretty much because his tooling has too much slop (thousanths) in his opinion, and getting HSS, straight cutting a gear, and having it heat treated may be a waste of time and cash if it's too sloppy. I'll try to measure some gears on the next manual trans I take apart to determine slop, but I was thinking, what if engineers designed a pretty decent level of flexibility in the trans already? If, for instance, the input and output shafts are both the same size/design, and there's enough room in the trans case, why not just pull a 1.75 2nd or 2 3rd, flip it, and have a nice low OD gear? Does anyone have any experience w/ this? Maybe it'll work w/ a little machining?
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 04-05-2007, 06:10 PM   #2
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For hondas it is a very common practice to use my hf third gear as a fourth gear. So, it is very common to swap gears around willy nilly like this. There is a lot of wiggle room with these transmissions, you can even swap betweem hydro and cable clutched trannies because they kept the design the same when they messed with the clutch (though I do think the finals are not swappable between the two types).
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Old 04-05-2007, 07:04 PM   #3
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Sweet! Are you talking about a swap and flip to get an inverse ratio, or just moving gears around?
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Old 04-05-2007, 07:55 PM   #4
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Just switching, I don't think the flip will work, as I've never heard of it being done.
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Old 04-05-2007, 08:35 PM   #5
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I'm hoping it does. And since most swaps seem to be acceleration oriented, I don't think many would've tried it yet since we can't accelerate quickly by taking a 2:1 2nd gear combo, flipping it, and using it as an OD w/ a .5:1 ratio. Even it's not a lego situation, I bet machining 'em to fit would be easier than cutting gears. Hopefully...
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Old 04-06-2007, 12:30 AM   #6
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Gear Mods

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Originally Posted by omgwtfbyobbq View Post
I asked my uncle about custom cut gears yesterday, and he didn't seem too enthusiastic. Pretty much because his tooling has too much slop (thousanths) in his opinion, and getting HSS, straight cutting a gear, and having it heat treated may be a waste of time and cash if it's too sloppy. I'll try to measure some gears on the next manual trans I take apart to determine slop, but I was thinking, what if engineers designed a pretty decent level of flexibility in the trans already? If, for instance, the input and output shafts are both the same size/design, and there's enough room in the trans case, why not just pull a 1.75 2nd or 2 3rd, flip it, and have a nice low OD gear? Does anyone have any experience w/ this? Maybe it'll work w/ a little machining?
Here is a link to a gear mod from a friend I have been in contact with for some time. Lots of good pics. His machinist used wire Electrical Discharge Machining to modify the gears. I decided on grinding for my parts, mainly for local shop capability and cost. A lot of work for a .545 vs .770 fifth gear but lowers my engine RPM by 30%.

http://mypeoplepc.com/members/tleone/gears/

P.S. omg, please reply to my PM sent you earlier this week.
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Old 04-06-2007, 07:12 AM   #7
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Custom gear making is VERY expensive.

Do a google search on "gear hobbing" - this is the method of manufacture. Flat out milling a gear with involute teeth - yikes, that would be a nightmare.

The problem with most transmission gears is that the teeth are helical. This actually SOLVES a problem of teeth wearing down (I can further delve in to the dynamics of gear trains if you'd like ) and noise. The reverse gear in most transmissions has straight cut teeth, and we all know how that sounds. Imagine if all your gears sounded like that (whiiiiiiiiiiiiiiiiiiiiine!).

Custom racing transmissions sometimes use straight cut gears with dog engagement instead of helical gears with synchro engagement.
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Old 04-06-2007, 07:33 AM   #8
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I decided on grinding for my parts, mainly for local shop capability and cost. A lot of work for a .545 vs .770 fifth gear but lowers my engine RPM by 30%.
CO - you're having this done to your car?
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Old 04-06-2007, 07:35 AM   #9
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As for cost, the guy who did the custom aero-modded XFi machined his own 5th gear ratio. He was quoted $2500 to have a shop do it.

Modified Metro XFi: throwing convention to the wind

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Old 04-06-2007, 12:02 PM   #10
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Switching gears would be awesome. Not sure about toyota's transmissions, but vw's transmissions have separate gears, so I just need to figure how to get the synchros working. Thanks for the help everyone!
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