Straight-Cut Gears

[hammerfang]

i recently went in a ride in my friend's 02 wrx which i have to say was quite an experience, COBB tuning 2.5 liter kit, all the internals r forged, new turbo and intercool, 2400 lbs clutch and lightweight flywheel, tuned to run on 116 octane fuel, no cat, but the most interesting thing i found was that the first 3 gears were straight cut and the incredible sound they made. i had heard of such gears but never actually rode in a car with them and im still not 100% sure how they exactly work and there benefit, could anyone fill me in on some details, and does anyone have a BMW with them installed?

[BueckDich]

Pretty much every car on the planet has straight cut gears. Its called reverse.

The noise is annoying as hell, why anyone would want straight cut forward gears is beyond me.

The main perk of them is clutchless shifting, you just ram it into the next gear.

[Blackwidow]

http://auto.howstuffworks.com/gear2.htm

This is a straight cut:


Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth. The advantage is clutchless upshifts.

most car gears are helical

When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement.

[hammerfang]

i was under the impression that straight-cut gears were a good deal stronger, thats y my friend got them, he blew out 2nd gear once and 3rd gear twice

[Glucas21]

The straight cut gears are much stronger, which is why most manuel transmissions used in American muscle cars from the 60'sand 70"s had them. Most serious race cars still use them, its just that they made to much noise for daily drivers so helical gears were used.

[BMWBry]

Thats the whining noise in the 9 minute M3 GTR on the Nurburing video that many have seen. The car must sound incredible like that. I such a beautiful whine at 6,000+ rpms.

[BueckDich]

Originally Posted by Lucas21

The straight cut gears are much stronger, which is why most manuel transmissions used in American muscle cars from the 60'sand 70"s had them. Most serious race cars still use them, its just that they made to much noise for daily drivers so helical gears were used.

It's not so much that they are stronger, but that the transmissions in Subarus are notoriously weak when you abuse them. Clutch drops = dead tranny.

[BMWBry]

Well I wouldn't expect many transmissions to last dumping the clutch on a AWD car.

And damn that gives me a good idea for my tranny rebuild coming at the fall.