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Old 02-20-2010, 06:57 PM   #1
Whoa!ShutItDown
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Default How exactly does a gear break?

This seems like a stupid question, but do you have to grind a gear to do damage? Would shifting really fast/hard damage gears if the clutch is fully pressed in? And just out of curiosity, say you have 400hp on a stock 5mt and put your foot to the floor in first gear, could all of the teeth be broken off from too much power? I saw a gallery of messed up WRX transmissions and one picture showed 2 gears(still in the tranny case) with no teeth on them, were these people just bad drivers?
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Old 02-20-2010, 07:03 PM   #2
kakarotoni
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well if you disengage the clutch really fast without timing it right then yes that does put a lot of shock on the gears. If you let your friends drive your car, yes that could mess up your gears. If you clutch dump at 3k rpm or above that could destroy your 1st gear. And if you mod your car faster beyond what the tranny could handle that could also destroy gears.

Just time your shifts right and be kind to your car.
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Old 02-20-2010, 07:07 PM   #3
XmikeX
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Quote:
Originally Posted by Whoa!ShutItDown View Post
This seems like a stupid question, but do you have to grind a gear to do damage? Would shifting really fast/hard damage gears if the clutch is fully pressed in? And just out of curiosity, say you have 400hp on a stock 5mt and put your foot to the floor in first gear, could all of the teeth be broken off from too much power? I saw a gallery of messed up WRX transmissions and one picture showed 2 gears(still in the tranny case) with no teeth on them, were these people just bad drivers?
you wouldnt happen to listen to acacia strain would you? and i think about this sometimes, why would the geard get messed up if you putthe clutch in and disengaged the car from running...and if ou just stomp on the gas from a roll would it strip the gears if you add power
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Old 02-20-2010, 08:59 PM   #4
vinxH
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Quote:
Originally Posted by Whoa!ShutItDown View Post
This seems like a stupid question, but do you have to grind a gear to do damage? Would shifting really fast/hard damage gears if the clutch is fully pressed in? And just out of curiosity, say you have 400hp on a stock 5mt and put your foot to the floor in first gear, could all of the teeth be broken off from too much power? I saw a gallery of messed up WRX transmissions and one picture showed 2 gears(still in the tranny case) with no teeth on them, were these people just bad drivers?

shock load is what breaks the gear. drive smooth and things will be fine.

contrary to popular belief, it's not "too much" power that causes the gears to break. with a larger turbo, usually the bottom-end of the RPM range will be slow, but out of no where a bunch of power comes in once the turbo starts spooling.. = shockload. if you pop the clutch instead of engaging it smoothly, that creates shockload to the gears as well. if you downshift without rev-matching, that does the same thing.

it's really not that easy to break the gears unless you were asking for it. from what i have gathered, the people who break their gears will typically say they weren't driving it hard, but when you see how they drive, they DO drive it hard.. they just dont know it.

and to answer your question about the 400hp comment... its not HP that breaks the gear, its torque. Torque is what causes shockload. with that being said... if you are in the 400hp range, chances are you are also in the 350tq range with your 04 WRX... which is still OK depending on how smooth your powerband is. but if you want to have any fun with 400hp at all, don't expect the gears to last with that much power.

Last edited by vinxH; 02-20-2010 at 09:09 PM.
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Old 02-20-2010, 10:44 PM   #5
evan_impreza
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acacia strain ftw
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Old 02-20-2010, 10:46 PM   #6
XmikeX
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Originally Posted by evan_impreza View Post
acacia strain ftw
this
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Old 02-20-2010, 10:54 PM   #7
Newbuggy
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As stated above its shockload that breaks the gears. I broke my trans a year ago. I was coming home from a stressful day at work. I turned down my street and decided to see how fast I could get to 60mph. I took off brought it up to redline then stuffed it into second dumped the clutch and bam second gear stripped. The input and counter shaft can actually bow under the stress load. This pushes the meshing surfaces between the teeth to the outer and weaker part of the teeth. Which is why big rigs have twin counter shafts to cope with the extreme torque the diesels put out.
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Old 02-20-2010, 11:41 PM   #8
Liquidr1
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Well ive been pondering about all the transmission storys on the forum as well.

Well i want to get something out and the open here. Lets just say that all im ever going to do to my 09 WRX is just a turbo back exhaust and stage 2 tune. Now, we all know that subaru supposedly strengthened the trans on the 09.

Now, i dont EVER lauch my car nor do i ever go to the drag strip. I just enjoy having a good reliable powerful daily driver. All i ever do is take off normally and romp through the gears.

My question is at just stage 2 levels, honestly, what chances do i really stand of screwing up my transmission given the above statments?


EDIT: i have also not found any blown 09 WRX transmission threads around here or on clubwrx.net. People on here/ youtube seem to be taking their stock 09s to the track and running consistent mid to low 13 second passes and that one guy hitting 12.9 in his stock 09. All this and no stories of transmission failures yet. How long until we can assume that subaru has significantly upgraded the gear sets in the 09 wrx to the point that we can somewhat stop worrying as much about the 5MT.
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Old 02-21-2010, 12:08 AM   #9
Whoa!ShutItDown
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3750 and the Dead Walk are their best albums imo, alot of songs on Continent sound the same. I saw them at the Penny Arcade in Rochester 12/07, their last song came on around 12:30 at night and bar stools literally went flying. That place was crazy. Then again at Xtreme Wheels in Buffalo which is a skate park with a stage next to it, all inside.

Bust as for dumping the clutch, I tried it once and was not expecting the car to jump as much as it did (I dont know why I thought that) and I lost my footing and stalled. I started driving and after I realized my tranny was fine, swoosh swoosh swoosh which only got faster. I must have knocked a pad loose or something because it stopped when I hit the brakes.

I'm still on the stock clutch (I think) at 70,100. I was told to start saving for a new clutch by my friends who drove the car last March, I think I'll keep going though. Sometimes it seems like it doesnt catch until my foot is off the pedal, but it doesnt slip until I try to go from like 3k (never dropping the clutch though). I wont lie and say I dont drive hard, I love seeing how fast I can get to the speed limit, or 7 over. But since I have read countless threads on 5mt's breaking, and have no money, I do everything I can to reduce wear on it (when not inducing it). If it wasnt for reading old posts I would never let the clutch out in neutral before downshifting
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Old 02-21-2010, 12:13 AM   #10
rkramer
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Quote:
Originally Posted by Whoa!ShutItDown View Post
This seems like a stupid question, but do you have to grind a gear to do damage?
to answer that question, you could grind a gear all day long and your gears would be perfectly fine. When you shift and grind, you are never actually moving gears, all your gears are already engaged. Your synchros and engagement dogs on the other hand... that is what you hear grind, NOT the gears.
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Old 02-21-2010, 12:14 AM   #11
vinxH
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Quote:
Originally Posted by Liquidr1 View Post

My question is at just stage 2 levels, honestly, what chances do i really stand of screwing up my transmission given the above statments?
Every time you change gears, engage it smoothly. Chances are you will be fine if you follow that one rule. If you want to be extra nice, don't stab the throttle to the floor out of no where.
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