Transmission Questions (GT4 #10390) | FerrariChat
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Transmission Questions (GT4 #10390)

Discussion in '308/328' started by newto308, Mar 21, 2010.

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  1. newto308

    newto308 Karting

    Mar 20, 2007
    92
    McLean, Virginia
    Full Name:
    Chris
    #1 newto308, Mar 21, 2010
    Last edited by a moderator: Sep 7, 2017
    I got my engine stand back from the fabricator and I've started putting the transmission back together. I've been reviewing a couple of different parts manuals and I've got a few questions:

    First, it does not appear there is a gasket required between the transmission case and the Differential Case Cover or the Speedometer Gear Cover Plate (see photo below). I was planning to use some high quality permatex here. Is this correct?

    Second: I have read that the seals (two "O" rings) that seal the shifting shaft are notorious for leaking. I thought I would replace them while I have the case apart. Is there really just one "O" ring seal between the transmission sump and the engine sump, and another "O" ring seal between the engine sump and the exterior of the case? Seems like there should be more to it. Did I miss something?

    Third: My workshop manual says that the differential taper bearings require pre loading. This has me a bit confused. Can anyone explain how I would be able to measure this? The manual says, "with new bearings and a load of 2,280-4,030kg., the pully should move slowly in a uniform movement. If not, duly vary the spacer thickness (the lateral spacer I assume) until the correct preload is obtained."

    ......Chris
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  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,846
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Mar 21, 2010
    Last edited: Mar 21, 2010
    It's telling you that the thickness of spacer 7 in Fig 13 on page D20 is selected so that the force "P" as shown in Fig 13 is in the range between 2.28-4.03 kilograms (to use the US decimal period separator) to (just slowly) rotate the differential assembly (with new bearings) under the assembly conditions specified in the text on page D21. Since the diameter of pulley 9 is given as 200mm, this corresponds to a moment of 19.8 - 35.0 inch-pounds. The pulley tool, with a fixed weight attached by an unwinding cord, provides a constant moment, and the weight should fall at a near-constant rate (i.e., "uniform movement") which is easy to judge visually.
     
  3. newto308

    newto308 Karting

    Mar 20, 2007
    92
    McLean, Virginia
    Full Name:
    Chris
    #3 newto308, Mar 22, 2010
    Steve:
    Thanks, your explanation helps a lot. Let me see if I passed the test........Depending on the thickness of the spacer, the friction/tension exerted on the bearings will allow the prescribed weight to fall too fast, too slow, unevenly. So, if I have the correct amount of tension (preload) on the bearing, the weight should fall evenly and not accelerate or decelerate as it falls, correct?
    ....Chris
     
  4. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    7,022
    Groton, MA
    Full Name:
    Verell Boaen
    #4 Verell, Mar 22, 2010
    That's correct.

    The 'gotcha' is that the test is supposed to be done with the ring gear free, ie: not engaged with another gear. Thus only the drag of the differential bearings & seals is being measured.

    This means the preload has to be set BEFORE the main & lay shafts are installed in the tranny!
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,846
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Mar 22, 2010
    Last edited: Mar 22, 2010
    I'd say this a little differently. It really isn't the speed of the weight falling that you are trying to measure, it's determining the amount of weight that will just cause the pulley to continuously spin (i.e., with any less weight, the pulley would be stationary and the downward velocity of the weight would be 0), and the (slow) spinning/falling action should be "smooth" (no jerking, no start/stop).
     
  6. newto308

    newto308 Karting

    Mar 20, 2007
    92
    McLean, Virginia
    Full Name:
    Chris
    #6 newto308, Mar 30, 2010
    Thanks guys! This helps a lot. ......Chris
     

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