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  1. #1
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    Question Sudden Drivetrain Hum at the Track - Broken Component?

    Setup - FBO E92, 6MT, NT05R DRs, and wavetrac LSD

    Did a good 10 runs or so at the 1/4 track, one of which had a hard pop during launch. I got ittermittant wheel hop on a run, but nothing bad. On the last run, I could hear a loud hum at the too of third and into fourth gear.

    When dirving home I noticed at low rpms there is a vibration and an audible him throughout the RPM band.

    I've mounted the center bearing upside down on the frame on my old car (e92) and it feels like that vibration, just not as bad (but just as audible). I put the car on jack stands and can't visually see anything wrong with the rear axles, diff, or diff output.

    Any ideas on how to diagnose this and what could be wrong?

    Thanks
    700 and change

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    COBB AP ProTune by Bren of ///Bren Tuning
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    When the vibration is present, how does it react to modulating the gas pedal? Is the vibration frequency proportional to vehicle speed or engine speed? How does the oil in your diff look?

    I had a CV joint go bad once and it was fine if I was under power or coasting, but if I was just at part throttle, cruising, it would vibrate like a son of a $#@!.

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    Most likely rear half shaft/cvs...if it is its time for either DSS axles or get some used ones to replace your current ones and call it quits on 1/4 mile racing with this car..is your car lowered?

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    Click here to enlarge Originally Posted by benzy89 Click here to enlarge
    dont know why you got neg repped +1
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    Click here to enlarge Originally Posted by dzenno@ProTUNING Freaks Click here to enlarge
    Most likely rear half shaft/cvs...if it is its time for either DSS axles or get some used ones to replace your current ones and call it quits on 1/4 mile racing with this car..is your car lowered?
    My car is on the stock sport suspension.

    What makes you believe it is the half shafts and how can I test for damage (outside of removing the boot)?
    700 and change

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    Based on what you described and what you were doing (launching, wheel hop) that's the most likely outcome. I'd get the car up on the lift and check for play first. To really check you need to get the half shafts down and see if they have smooth movement in the CVs or if they're binding. Its usually pretty obvious.

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    Click here to enlarge Originally Posted by crazylegs Click here to enlarge
    dont know why you got neg repped +1
    LOL thanks & me neither, and it was shortly after I posted that up.... Figured Rick would be the best to comment since his product specifically deals with preventing wheel hop & associated damage.
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    Click here to enlarge Originally Posted by dzenno@ProTUNING Freaks Click here to enlarge
    Based on what you described and what you were doing (launching, wheel hop) that's the most likely outcome. I'd get the car up on the lift and check for play first. To really check you need to get the half shafts down and see if they have smooth movement in the CVs or if they're binding. Its usually pretty obvious.
    I had the back end up yesterday, and the wheels moved easily and together with no obvious binding. I didn't remove the shafts, however.

    I can take them off if need be.
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    Update -

    I took it for a drive and noticed that the vibration was rpm, not speed dependent and I could feel it at 1500 rpms when in neutral.

    If I hold the rpms (1.5-4k rpms) in neutral then press the clutch, the car vibrates and the engine note gets loud (sounds like it is resonating through the drivetrain).

    This leads me to believe it is in the rotating assembly. I had my DMFW resurfaced (about 8k miles on it since new) and running a Spec 2+, with about 3k miles on it.

    Thoughts on best next steps?
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    I have no help to give, but wanted to offer a Click here to enlarge in sympathy. Click here to enlarge

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    I would check the flywheel next.

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    ^ what he said. The dual mass center might have broken, causing some out of balance in the rotating mass.

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    Don't forget the rubber joint on the drive shaft "guibo"? and diff mounts. I would look at those items first before the flywheel. I've had my flywheel make noise after the track, but it would work itself out in 10 or so miles after the track.

    Crap. Thought about motor and trans mounts too. Any one of those can be an issue.

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    Click here to enlarge Originally Posted by Ryan Mills Click here to enlarge
    Don't forget the rubber joint on the drive shaft "guibo"? and diff mounts. I would look at those items first before the flywheel. I've had my flywheel make noise after the track, but it would work itself out in 10 or so miles after the track.

    Crap. Thought about motor and trans mounts too. Any one of those can be an issue.
    Those are good ideas, but when in neutral, the only things in play are the rotating assembly (and trans input shaft).

    I'm beginning to think it's the FW/clutch components, or the crank. I doubt it's the crank, as I haven't heard of any failures, especially at low 4xxwhp on a tune that doesn't knock.

    For those who have had DMFW failures, what were the symptoms?
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    Checked codes and it throws a P2C2E. When I clear it, it returns right away. Does anyone know what that code means (I don't see it in my lookup)?
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    The code description reads - "lambda probe before catalyst 2, sheer test."


    I assume that relates to a rear O2?
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    Click here to enlarge Originally Posted by The Ghost Click here to enlarge
    The code description reads - "lambda probe before catalyst 2, sheer test."


    I assume that relates to a rear O2?
    No idea, bump.
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    I would think "before catalyst 2" would refer to the front (primary) O2 sensor in bank 2. As for WTF "sheer test" means, I'm guessing that one didn't translate from German very well.

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    Someone suggest a mad motor mount, so I checked them and both mounts appear solid, all bolts in place, and when I raise the engine slightly using a crowbar near the mount it moves back/forth with resistance.


    It vibrates at 2krpms in neutral and is amplified (soundand vibration) when the clutch is depressed. I wouldn't think the mount would cause this, especially under zero load like this in a stationary car. What symptoms did the broken mount exhibit for you?


    Crank pulley has no play; verified operation and tightness of bolt.


    My gut says the DMFW is broken somehow, although it only has 10k miles on it (it was resurfaced though). Can someone find the link to a DMFW faure thread. I don't know what symptoms they had.
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    DMFW....I've seen them get ugly and make a violent exit via the bellhousing in the past, the symptoms you describe make me lean heavily towards that being the issue.The fact that it's rpm and not speed dependent isolates it pretty clearly. If you dig back a bit, there's a thread started by uniter featuring pics of the internals of his DMFW I had cut apart...in the name of science...one must dissect to fully understand.....

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    Update - I put my car way up on four points to begin removing the transmission when I noticed the bolt that secures the front driver's side of the diff sheared, leaving the diff cocked. This def could be the cause, although I would not think it'd affect the vibrations in neutral outside of perhaps harmonics being transferred to a loosely-hanging diff.

    I'm going to source a replacement bolt tomorrow and see if this resolves it.
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    What is the class rating stamped on the head of the bolt? 8.8, 10.9, 12.9?

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    I was pretty close Click here to enlarge should be an easy fix

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    Click here to enlarge Originally Posted by ajm8127 Click here to enlarge
    What is the class rating stamped on the head of the bolt? 8.8, 10.9, 12.9?
    It is 10'9.
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