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Thread: Throttle Shaft Leaks - cost me ALL boost?

  1. #1
    Junior SCH Member
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    Dec 2012
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    3

    Throttle Shaft Leaks - cost me ALL boost?

    I am new to supercharging. Bought a rebuilt SN98, looks good, turns smooth, impeller looks good.
    Installed it on my 5.0, rebuilt my old Holley 4150 to blow thru. I decided not to mess with the throttle shaft bushings even though they were a little loose. No Boost.
    Checked for leaks with pressure test, cleaned everything up except throttle shafts still leak. Could this cost me ALL of my boost?? Checked with 2 gauges while driving, 1 on Paxton, 1 on intake manifold. Tons of vacuum- not even 1 psi boost. Impeller at intake side cannot be spun by hand when belt is on. Supercharge sounds nice, almost no sound at idle (but airflow shown by leaks with soap test), slight whine at 4k. Can all my problems be throttle shaft bushings??

  2. #2
    Junior SCH Member
    Join Date
    Jun 2009
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    30
    It seems that you should have boost at the blower unit, even with some leaks. I doubt you throttle shafts are leaking enough to affect anthing even if you had boost. Throttle shaft bushing should not cause much of a loss of boost, it just lets fuel squeeze out of the shafts and makes you intake dirty.

    Sounds like the blower balls are slipping internally when the rpm comes up. You may have to add a shim or two to tighten up the pressureon the balls. It could be a nuimber of other things as well, like belt tensioner not giving enough pressure.

  3. #3
    Junior SCH Member
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    Dec 2012
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    suede57ford - you were correct. Because it was just rebuilt (by previous owner) I assumed it was okay but the pre-load was low. Shipped it once, ran great for 5 seconds under boost then quit again. Checked pre-load and it was low again. I assume that one of the races must have not been fully seated. Shimmed it again to 40 in lbs and it runs awesome!! First supercharger....will never build a rod without one again.....THANKS This forum has been a great help.

  4. #4
    Senior SCH Member vinces427bb's Avatar
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    Jul 2011
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    Los Lunas, NM
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    glad you found the real issue

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