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Axle size mismatch

This is a discussion on Axle size mismatch within the GTO forums, part of the Vehicle Specific category; ...

  1. #1
    Grand Imperial Wizard Sarge's Avatar
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    Axle size mismatch

    Interesting read....
    Corvette Quarterly
    www.cqmag.com
    Winter 2008 (pg60)
    Technicalities by Don Sherman
    Teaching ZR1 Not to “Dance” During Takeoff
    HIP HOP. NOT.

    When your mission is accelerating from zero to 60 mph in practically nothing flat, every 10th of a second counts. During ZR1 development, Corvette engineers were dismayed to find that zero-to-60 performance was less than anticipated. Major increases in power, torque and traction over the Z06 were not delivering the expected reduction in acceleration times.

    “The problem,” reveals Corvette engineering development manager Dave Wickman, “was power hop.” During launch, the ZR1’s rear tires were sticking and releasing in an unfavorable manner, which excited the entire driveline into a torsional resonance.

    All mechanical systems resonate at some natural frequency. Think of a plucked harp string, a ringing church bell or the rim of a martini glass stroked by a damp finger. From the crankshaft to the rear tire patches, the ZR1’s driveline constitutes a mechanical system with a particular natural frequency. When excited by the staccato torque/no-torque conditions that follow an abrupt first-gear clutch engagement, developmental ZR1 mules were resonating – hopping – at the driveline’s natural frequency.

    The traction characteristics of the new Michelin Pilot Sport 2 radials, combined with the torque characteristics of the new LS9 supercharged V8, the suspension dynamics provided by ZR1’s softer spring rates and the damping properties of the electronically controlled magneto-rheological (MR) shock absorbers, had driven the new Corvette prodigy into an uncharted corner of the performance map. Something had to be done.

    Wickman’s development team went to work. “Substantially increasing the driveline’s stiffness would shift its natural frequency away from the resonance point,” notes Wickman. “Unfortunately, greater stiffness usually means added mass, something we strive to avoid.

    “The smarter solution was decoupling the left and right sides of the driveline by using half-shafts with significantly different natural frequencies. In production, the ZR1’s left half-shaft is a 40mm (1.57-inch) solid steel rod while the right one is 33mm (1.30-inch) in diameter, yielding a 1.5 times difference in stiffness and, therefore, natural frequency.”

    Programming the MR dampers was the second half of the solution. Corvette ride and handling engineer Jim Mero explains: “With the car at rest, the dampers provide essentially no damping. So we created a lift-dive algorithm (software) that would automatically configure the suspension for optimum launch traction.”

    Following experimentation, the optimum arrangement turned out to be the full 100 percent of available rebound damping in front and 30 percent of maximum jounce damping at the rear. So, when the ZR1 settles back on its haunches following an abrupt clutch engagement, the rearward pitch motion and resulting damping forces supplement the rear tires’ static load. That maximizes tire-to-road adhesion.

    The icing on the cake is ZR1’s traction control system. Mike Petrucci, responsible for chassis controls development, explains: “The section of the traction control logic applicable to launching the ZR1 aggressively from rest is programmed to allow a fruitful amount of rear-wheel slip as long as the steering is pointed straight ahead. This allows owners to experience entertaining street performance. By keeping the traction control actively engaged, they should be able to come very close to the 3.4-second zero-to-60 acceleration figures we’ve measured in ZR1s under ideal circumstances.” Problem solved.
    ----------------------------------------------------------------
    Makes sense to me......

  2. #2
    Grand Imperial Wizard Sarge's Avatar
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    These are the latest and greatest from East Texas Muscle....see the size variance
    Drag bags

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    Member Tide's Avatar
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    Nothing special
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    So riddle me this, and it's something I've been thinking about with our GTOs and the different weighted rear half shafts...

    Front wheel drive cars suffer torque steer as a result of drive shafts / CV joints that do not weigh the same or are not the same length. The corrective fix, or rather to minimize the effect, is to have equal length / weight shafts so that equal power (in theory) is put to the ground at each wheel. Also, a limited slip differential to ensure the proper power is put to the right wheel.

    That said, since our cars have a limited slip (if I remember correctly), the diff is going to send the power to the wheel with the most traction, though the wheel with the least traction is still going to spin - nothing you can do about that really. The only time both our wheels spin is when it's a straight line. Although my dif could be blown, however, I don't think so, as I still leave two equal length black marks on a straight burnout. If I hammer down on it in a low speed turn, generally the inside tire spins more than the outside - but that depends on when i put the power down, I believe.

    Long story short, why wouldn't different weighted shafts cause one side to spin more as a result of less initial resistance due to the lower unsprung weight? Or am I looking at it wrong? I might be making it more complicated than it really is. This is my first time dealing with an independent rear suspension car, so I may be just looking at it completely incorrectly.
    Last edited by Tide; 12-23-2008 at 12:32 PM.

  4. #4
    Member Texas Jack's Avatar
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    You guys may be on the road for fixing my nightmare!!!!!!!!!!

  5. #5
    Grand Imperial Wizard Sarge's Avatar
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    Quote Originally Posted by Tide View Post
    So riddle me this, and it's something I've been thinking about with our GTOs and the different weighted rear half shafts...

    Front wheel drive cars suffer torque steer as a result of drive shafts / CV joints that do not weigh the same or are not the same length. The corrective fix, or rather to minimize the effect, is to have equal length / weight shafts so that equal power (in theory) is put to the ground at each wheel. Also, a limited slip differential to ensure the proper power is put to the right wheel.

    That said, since our cars have a limited slip (if I remember correctly), the diff is going to send the power to the wheel with the most traction, though the wheel with the least traction is still going to spin - nothing you can do about that really. The only time both our wheels spin is when it's a straight line. Although my dif could be blown, however, I don't think so, as I still leave two equal length black marks on a straight burnout. If I hammer down on it in a low speed turn, generally the inside tire spins more than the outside - but that depends on when i put the power down, I believe.

    Long story short, why wouldn't different weighted shafts cause one side to spin more as a result of less initial resistance due to the lower unsprung weight? Or am I looking at it wrong? I might be making it more complicated than it really is. This is my first time dealing with an independent rear suspension car, so I may be just looking at it completely incorrectly.
    We are looking specifically at the wheel hop/traction in a straight line/powering out of a corner here. In a turn under power the limited slip will allow for a variance in rotational velocity between the two wheels. In a straight line equal power is applied to both wheels....
    What the harmonics issue addresses is the tires "sticking and releasing"....this is a phenomena of a LSD rear end known as "wheel hop".
    Wheel Hop has been addressed in the past mainly by beefing up the rear end chassis to increase down force on the tire to make it stick and not release. We have done this with heavy duty springs/shocks/bushings/drag bags....and have had success. But what we (manufactures and the hot rod community) have learned is by manipulating the harmonics of the axles and addressing the drive line shock of a launch we can get the same results/ better results of eliminating this "sticking and releasing" AKA Wheel Hop in the LSD as the article is a testimony of that success. We also see this success in eliminating wheel hop in our very own GTO community and these new axles.
    Two things come into play in wheel hop.
    1. The harmonics described above.
    2. The engine torquing over changing the geometry of the drive line....introducing a "shock" to the drive line.

    So to address/treat this condition we have all the suspension modifications treating the symptoms but not the cause. To treat the cause we have learned and have real world success by changing out the axles to these harmonically balanced axles ( From East Texas Muscle is where I got mine) and by eliminating the drive line shock by installing a torque dampener. Again the dampener can be Poly Motor Mounts or a "Stiffy"...I went the "Stiffy" route as I didn't want vibration in the cabin/steering wheel sometimes associated with hard motor mounts....I got mine from Jim Gravana...
    http://gravanatuning.com/434/2/430/0...e_5.7_RWD.html
    I think they also have a Stiffy for the 05's and 6's now but check with them....or there are a few Motor Mount solutions out there from various manufacturers....
    Don't know if I did worth a damn explaining...but it is 5:22 a.m. December 24th and I have to go Christmas shopping in 30 minutes....I bet I'm the only guy out there getting his Christmas presents on the very last day

  6. #6
    Member Texas Jack's Avatar
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    Sounds good to me and yes i have to go shopping when i get to Dallas to see the G kids, MC all.
    Last edited by Texas Jack; 12-24-2008 at 05:27 AM.

  7. #7
    2001 ws6 6-speed david_viny's Avatar
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    2001 Pontiac Trans Am WS6

    89-97 Ford t-birds have different diameter half shafts on each side. Wonder if it was for the same reason? Are GTO shafts the same size on both sides?

  8. #8
    Junior Member east TX muscle cars's Avatar
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    2005 corvette 2004 gto

    Quote Originally Posted by david_viny View Post
    89-97 Ford t-birds have different diameter half shafts on each side. Wonder if it was for the same reason? Are GTO shafts the same size on both sides?
    yes they are from the factory

  9. #9
    Junior Member east TX muscle cars's Avatar
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    Quote Originally Posted by Sarge View Post
    We are looking specifically at the wheel hop/traction in a straight line/powering out of a corner here. In a turn under power the limited slip will allow for a variance in rotational velocity between the two wheels. In a straight line equal power is applied to both wheels....
    What the harmonics issue addresses is the tires "sticking and releasing"....this is a phenomena of a LSD rear end known as "wheel hop".
    Wheel Hop has been addressed in the past mainly by beefing up the rear end chassis to increase down force on the tire to make it stick and not release. We have done this with heavy duty springs/shocks/bushings/drag bags....and have had success. But what we (manufactures and the hot rod community) have learned is by manipulating the harmonics of the axles and addressing the drive line shock of a launch we can get the same results/ better results of eliminating this "sticking and releasing" AKA Wheel Hop in the LSD as the article is a testimony of that success. We also see this success in eliminating wheel hop in our very own GTO community and these new axles.
    Two things come into play in wheel hop.
    1. The harmonics described above.
    2. The engine torquing over changing the geometry of the drive line....introducing a "shock" to the drive line.

    So to address/treat this condition we have all the suspension modifications treating the symptoms but not the cause. To treat the cause we have learned and have real world success by changing out the axles to these harmonically balanced axles ( From East Texas Muscle is where I got mine) and by eliminating the drive line shock by installing a torque dampener. Again the dampener can be Poly Motor Mounts or a "Stiffy"...I went the "Stiffy" route as I didn't want vibration in the cabin/steering wheel sometimes associated with hard motor mounts....I got mine from Jim Gravana...
    http://gravanatuning.com/434/2/430/0...e_5.7_RWD.html
    I think they also have a Stiffy for the 05's and 6's now but check with them....or there are a few Motor Mount solutions out there from various manufacturers....
    Don't know if I did worth a damn explaining...but it is 5:22 a.m. December 24th and I have to go Christmas shopping in 30 minutes....I bet I'm the only guy out there getting his Christmas presents on the very last day
    we have some bad ass motor mounts we just pucked up.!!!! here is a pic! these are 199.99 plus shipping. here is a quote from SCSS.
    "We have released a new set of motor mounts made specifically for the GTOs dubbed KAZA Engine Mounts. These engine mounts are made of high strength DOM steel, utilize enclosed poly bushing, and best of all - these are rebuild-able. Currently 1 set on my own twin turbo GTO and I love them. These are noticeably better than OE. There is virtually no flex of the engine. More power is translated to the wheels while minimizing losses due to engine movement."




  10. #10
    Junior Member east TX muscle cars's Avatar
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    orange
    2005 corvette 2004 gto

    also have a slightly softer one for street use and Trans mounts soon to come!!!!!

  11. #11
    Grand Imperial Wizard Sarge's Avatar
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    Got the stubs and axles today.....nice! As an old machinist (aircraft) I can tell you these are top notch high quality stuff.

  12. #12
    Impounded
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    Another good read to absorb more info. I think i have seen this on some 4wd vehicles. I know I worked on a yota truck once and one of the shafts was huge and the other was a twig...

  13. #13
    Senior Member qwkgto's Avatar
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    Quote Originally Posted by east TX muscle cars View Post
    we have some bad ass motor mounts we just pucked up.!!!! here is a pic! these are 199.99 plus shipping. here is a quote from SCSS.
    "We have released a new set of motor mounts made specifically for the GTOs dubbed KAZA Engine Mounts. These engine mounts are made of high strength DOM steel, utilize enclosed poly bushing, and best of all - these are rebuild-able. Currently 1 set on my own twin turbo GTO and I love them. These are noticeably better than OE. There is virtually no flex of the engine. More power is translated to the wheels while minimizing losses due to engine movement."

    Click for full size
    Click for full size
    Click for full size
    so these work well on a twin turbo setup?send me a set ill let you know...
    mods: custom built twins, built 408 w/l92 stock GM heads,GM matching intake,drag bags,frame ties,aluminum drive shaft, performabuilt 4l80e,Yank converter,ohios fastest and quickest 04-06 GTO 9.52 at 144mph. 1.50 60ft on stock rear end and shafts/suspension,on drag radials.

  14. #14
    Senior Member qwkgto's Avatar
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    Phantom Black Metalic
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    Quote Originally Posted by Sarge View Post
    Got the stubs and axles today.....nice! As an old machinist (aircraft) I can tell you these are top notch high quality stuff.
    keep us up on how they work I have ran alot of 10 second passes on the stock 05 rears,i think my luck will run out soon.

  15. #15
    Grand Imperial Wizard Sarge's Avatar
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    I will.....I am looking to a stronger "push" to the tires and of course longevity....I broke an axle in my old Willy's altered and hit the wall pretty damned hard.....that still is always in the back of my mind out about 600'

  16. #16
    Junior Member east TX muscle cars's Avatar
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    2005 corvette 2004 gto

    take some pics of those bad boys, because you got the first set of the NEW VENTED CV'S!!!

  17. #17
    Grand Imperial Wizard Sarge's Avatar
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    OK...by the way folks we have a sponsor for the GTO section....I want to thank and welcome East Texas Muscle Cars as the GTO section sponsor.....if Ed will sober up long enough we can get their banner up here....LOL....

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    Grand Imperial Wizard Sarge's Avatar
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  19. #19
    Senior Member qwkgto's Avatar
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    ok those look good,on the stubs where the splines are is that all one peice,or an adapter where it goes together? these look like a set ive seen from another vendor,i broke a set of 1000hp+ right where that rides on the needle bearing which go into the rear end housing.

    here is what it did to rear end

    wiped out lil side load bearings ,hard to beleive them lil bearings hold all the shit they do.I am not trying to stir up shit just pointing out what happened to me, dont do any dry hops without water ,I broke these with fuckin nittos not MT i was not going through water just doing alil dry burn out and car hopped i let out and nothing.this design is piss poor that stub needs to be made from one solid peice.

  20. #20
    Grand Imperial Wizard Sarge's Avatar
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    Those are two piece stubs....looks like heat played a bigger role than torque in your pics....what do you think?

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