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How bad is whine on decel?

This is a discussion on How bad is whine on decel? within the Drivetrain forums, part of the LSx Technical Help Section category; I recently installed a Yukon gear set: it's a 3.42 ratio with thick ring for a series 2 carrier (stock ...

  1. #1
    Member tici's Avatar
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    1998 M6 vert TA

    Unhappy How bad is whine on decel?

    I recently installed a Yukon gear set: it's a 3.42 ratio with thick ring for a series 2 carrier (stock automatic rear end).

    After the 1st install it was a little noisy on acceleratio and quite on decel.
    The drive pattern wasn't toat good as coast.
    100 miles later I readjusted the pinion position: now the drive pattern looks fine to me, but the coast side is not perfect.

    During acceleartion or when I keep the speed the rear end is quite, but during decel, especially in an high gear, it whines from 50 mph down to 30.
    It's really on - off: as soon as I reach 50 it begins
    If I downshift like in 4th it quites down.

    Backlash is right in the middle of what Yukon suggested (0.008"), all preloads are fine. Therer were no mechanical damages, no runout also...

    I have a 75-90 synthetic oil used for BMW limites slip rear ends and I was thinking to try a 75-140, in the hope to quite it down

    Is it bad? Do I have to worry? During coast there is almost no load on the gears so I think it's not too bad, it's just that noisy things are normally NOT OK!

    I don't even know what to adjust: I mean: if the drive pattern is fine and backlash also, what else to do?

    Here a picture with the contact patters: left with too much pinion shims (noisy drive), righ how it is right now (noisy coast).

    Thanks for every input!

    Stefano
    Last edited by tici; 01-17-2006 at 03:50 AM.
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    1998 M6 vert TA

    Ttt

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    Noise on coast is prefered over noise on drive. Adjusting the dif was the correct thing to do. What you have may just be a reflection of the manufacture of those gears. Im not sure why you have the on-off condition at 50. Is there a condition where the fuel cut-off is delayed and it corresponds with the MPH? This would give you a "delay" in the full coast mode.I have seen this in other fuel calibrations.

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    Member tici's Avatar
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    1998 M6 vert TA

    Fuel cut-off is enabled at 1900 rpm (= 85 mph in 6th; 55 mph in 5th; = 40 mph in 4th).

    Mhh... difficult to say. I could change those vaues so that it's never enabled and see.

    Well: it whines also if I don't completely get off the pedal. Do you know if DFCO is enabled by 0% throttle angle or also for higher values?

    What do you think of those contact patterns? I just can't imagine how to get the coast side so good as the drive side: if I move the pinion one pattern becoms good and the other bad...

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    Member tici's Avatar
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    1998 M6 vert TA

    ok I disabled DFCO and it doesn't change.
    It's definately a mechanical thing.
    I'll soon reopen the pumpkin to replace the oil (brake-in is finished and I'll put a thicker oil).
    I'll also check patterns and backlash...

    what else?

    I hope it's not already fu... up!

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    Again, I think its the nature of your set(the way it was cut). Don't know who made your gears but I have seen many aftermarket gears ( actually most)produce your kind of concern- OEMs as well.The minor throttle position is called float. Coast and float noise generally go together. Your patterns look alittle off on the coast side but I would not compromise the drive pattern to improve the coast.You load more significantly in drive and that should be your primary target. You may be surprised at the improvement the "real" oil brings. Check the shimming and go with it.As far as the throttle decay goes. I was not suggesting to eliminate the parameter, just giving an explanation as to why your noise is on/ off at a given point.That is , when the o throttle is met, you get more noise because you have full vehicle over-run/ braking.

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    1998 M6 vert TA

    The gears are supposed to be Yukon. But this was only te name on the box. Who manufactured them... nobody knows.

    Noise is vibration. Vibrations are waves... Maybe some part reaches it's resonance frequency somewhere around 50 mph (axles? Ring)?. Those are thick gears (3.42 ratio for a series 2 carrier); I don't know how good is this configuration compared to a series 3 carrier and a normal ring.

    If GM uses two carrier designs there should be a reason, don't you think?

    Stefano

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    1998 M6 vert TA

    Some news...

    After 500 miles the rear end makes some more noise. In drive also.
    I reopened the pumpkin again to see if everything was still ok and to fill it with a thicker oil (75W140).

    The contact patterns are the same but backlash went from 0.008" (what I set last time) to 0.012".

    All the bearings look good, they just lost some preload, what I think is normal.

    There is some metal mesh on the magnet (??)

    Each teeth should have lost 0.001" but I don't see any step or strange surface on them. Smooth and shiny.

    I know, there's nothing more to do. It'll remain noisy.

    Any idea if it's normal to loose so much backlash?

    Thanks - Stefano

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    Yes , its from a "seating in "of the shim pack and bearings. I would re-shim it tighter now that its appart and you can. What happened with the thicker oil?I would have thought that would improve the situation.

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    1998 M6 vert TA

    The thicker oil didn't change the fact that it whines. Now it just starts to whine at a different speed!

    I attached the different contact patterns I had. Maybe someone has a good idea.
    Left is how it was with an additional shim under the pinion. In the middle how it was with the stock shim, the right the same after a couple of 100 miles.

    I have the feeling that if I change the pinion depth I can adjust coast but mess up drive. Or the opposite. But I'll never get both sides just fine.

    Am I wrong?

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