Manual Transmission T56 | T5 | MN12 | Clutches | Hydraulics | Shifters

Gear-dependent vibrations

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Old Apr 9, 2008 | 10:19 AM
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Default Gear-dependent vibrations

Background..

RPM-Stage IV T56,
LS6 clutch,
Alum. flywheel
stock driveshaft
4.10's
Poly bushings everywhere
u-joints are all tight and greased
gear setup is good and within specs
there is a little bit of play on the output, but nothing the gear guy said was concerning at all.

If I'm driving around 60 in 6th, I get a mild high-freq. vibe, can be felt mostly through my butt. If I drop to 5th, the vibe is gone at the same speed. This also happens in 5th around 40-45(Not 100% on the speed, but it's around there)

I'm very familiar with identifying speed-dependent vibs, but not usually gear-dependent ones..

Ideas?
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Old Apr 9, 2008 | 02:50 PM
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5th and 6th driven gears are both on a common spool-type gear. That is, 5th&6th driven gear is1 part with two gear cuttings on it. It may be that the spline & journnal this gear is pressed on to attach it to the main shaft may not have a tight fit (anymore). It could also be a simple as a bent mainshaft. If you have lost rear gears or a propshaft in past history, a bent mainshaft is quite commonly a secondary damage.
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Old Apr 9, 2008 | 09:26 PM
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Fortunately, this trans was purchased straight from RPM, and there's been failures like the driveshaft or gears..

The PO drove it with a failing master & slave cylinder which caused other issues, so I'll have whatever shop I take it to (probably tick) look at 5th and 6th closely.. thanks.
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Old Apr 14, 2008 | 12:29 PM
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Paid more attention to it this weekend.. it'll do it in basically every gear at some speed...

I'd be kinda pissed if the mainshaft was bent from day 1...
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Old Apr 14, 2008 | 08:10 PM
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If the vibration is RPM dependent (does it at the same rpm in every gear) then the cause is AHEAD of the transmission......meaning it's being caused by the clutch/flywheel assembly or the balance of the motor. Most likely your clutch/flywheel assembly needs balanced.
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Old Apr 15, 2008 | 01:59 PM
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Originally Posted by jmm98LS1
Most likely your clutch/flywheel assembly needs balanced.
What kind of shop does this sorta work?
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Old Apr 15, 2008 | 05:25 PM
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Any decent machine shop will have balancing equipment to do this, should cost ya between $30-50 to do.
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