dunnojack

iTrader: (26)

I'm having a big argument with my friend that straight cut gears are stronger than helical cut gears. need feed back from actual knowledgable people please! thanks!

Wingless Wonder

iTrader: (7)

Straight cut gears are stronger. Helical cut gears cut down on noise which is why all modern passenger vehicles use helical cut gears.

The classic General Motors (Muncie) M22 'rock crusher' 4-speed transmission used in some high-powered Corvette applications in the '60s had helical cut gears but the angle was changed to provide more strength. Subsequently, the transmission was significantly louder in actual use compared with the Muncie M20 wide ratio or M21 close ratio transmissions (same gear ratios as M22).

Here's a wikipedia link to gears.

--
0==WW==0
"…axles of evil…" - george w. bush

dunnojack

iTrader: (26)

cool, anyone else? any pro's that work with trannys all day have an input?

04blkWRX

The straight gears result in a stronger transmission, but the gears are not any stronger. The difference is that straight gears only result in radial stresses, where helical gears develop axial stresses as well. That requires thrust bearings to keep them from moving relative to each other. Plus, stresses in two plains can result in a greater combined stress than the sum of their parts.

But as Wingless said, people don't like the noise.

Wingless Wonder

iTrader: (7)

That is a better way to categorize straight cut gears than the way I phrased it. Thanks for the clarification.

--
0==WW==0
"…axles of evil…" - george w. bush

slvrsubywgn

iTrader: (7)

We had the infamous "Rock Crusher" in our '55 Chevy Bel Aire, mated to a pumped up 327c.i. and a 4.10 rearend. Man would that thing move (alot quicker than my WRX back in the day, my dad raced me with it and blew me away, made it look like I wasn't even stepping on it), but they were also the whiniest gears I've ever heard! Those gears put up with alot of abuse (ALOT more than my WRX and I already blew the tranny in it) and never broke or had any problems.

dunnojack

iTrader: (26)

so the straight cut gears result in a stronger tranny than helical cut gears? can anyone explain why that is? i'm just trying to get more detail so i can shut my friend up good!

ride5000

http://www.cs.cmu.edu/People/rapidpr...sms/chpt7.html
http://www.automation.com/sitepages/pid1906.php
http://www.twistgear.net/page%20html/twistgear.html
http://www.mendeolatransaxles.com/mikes_gripes.php

bottom line:

helical has greater tooth contact, but introduces axial loads and thus loses some efficiency.
spur is more efficient, but noisier.

neither is necessarily stronger than the other.

GotBoost?

iTrader: (3)

I'm not trying to argue, but actually straight cut gears give you the most tooth contact at all times which is why they are much stronger.....helical cut gears are designed so when the gears mesh together, the teeth are meshing on one side, as they are separating from the previous tooth on the other as the gear rotates, thus giving you a quieter transmission, but not giving you the most tooth-to-tooth surface area contact.

Here's a little description of the different types of gears and their differences from an authorized PPG gear vendor/installer over on WRXF.
http://www.wrxfanatics.com/index.php?showtopic=35693

-Ted

ride5000

ummm.

did you read any of those links?

neither cut of gear is inherently stronger than the other.

PERIOD.

GotBoost?

iTrader: (3)

ok, I just read them....you're right, I obviously am no gear engineer.....ya learn something new everyday! Thanks for straightening me out.

BTW: HAPPY HALLOWEEN!

-Ted

Kay95

ya its not really helical or straight cut but more the size of the teeth
the big the stronger

monsterboy

Straight cut gears also allow for faster clutchless shifting. Although one could argue that the synchros in street cars are what really slow things down, but they just contribute to slowing down the helical gear clutchless shift. Straight cut way noisier and requires alittle more shove even to engage 1st. But sweet when you match all your revs up.

ride5000

you are confusing the cut of gear with the type of syncro. they are not related.. ie, it is perfect possible to have a straight cut synchro box or a helical dog box.