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Thread: Tranny Chatter

  1. #1
    Blessed be the lowered RickS's Avatar
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    Tranny Chatter

    Jame's post reminded me of a nagging problem.

    I had the 915 completely rebuilt (keeping the good stuff, of course) and had a new Sachs clutch and throwout bearing installed. In other words, it was the whole 9 yards. Now when the car is relatively cold and hasn't been driven much, it is quiet when sitting at a light in neutral, clutch out. When warm, same situation, the is a mild chattering sound, that will only go away when I put in the clutch. Any BTDT?

    Thanks
    71 914 3.0, 82 SC, ESR 376, RG 307

    "The problem with the world is, the ignorant are cock-sure and the intelligent are full of doubt." Bertram Russell

  2. #2
    I have had that happen , on a BMW trans , and a jeep trans
    I thought is was the throw out bearing , but it was only
    a adjustment on the cable, it was lose were it moves the arm.
    i know its not a Porsche but I hope it helps.
    1972 911t Coupe(being Restored)
    1973 911t Targa(parts Car)
    2001 Audi A4 Quattro
    2004 Ford F150

  3. #3
    Moderator Chuck Miller's Avatar
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    Rick,
    My newly rebuilt 915 is doing the exact same thing...

    This is what we think my problem is:

    There is a number of caged bearings in the trans that are quite expensive to replace...
    Sometimes a mechanic will change only the bearings that are obviously worn and save the customer some BIG money by not replacing the ones that seem OK ...
    Well, sometimes that bites them in the ass when the only bearings that are making noise are the one's he hasn't replaced.

    Not saying that's the case in your trans but it has happened...
    I would ask exactly what has been replaced new.

    Parts are getting ridiculously expensive !!!... To rebuild a 915 trans 'as new' (all syncros, sliders, sleeves, and all bearings... not counting shafts or gears) at a regular shop rate will cost you well over $2500.00 ! ... Lots of mechanics use as much 'good' stuff in your box as possible...

    Would like some of the pros to weigh in on this...

    Will let you know how mine comes out ... but it won't be for awhile... right now I'm just drivin the car

    Cheers,
    Chuck Miller
    Creative Advisor/Message Board Moderator - Early 911S Registry #109
    R Gruppe #88

    TYP901 #62
    '73S cpe #1099 - Matched # 2.7/9.5 RS spec rebuild
    '67 Malibu 327 spt cpe - Period 350 Rebuild

    98 Chevy S-10 Utility
    15 GTI Commuter

  4. #4
    Rick,

    The change in the noise between cold and warm is more than likely a function of oil viscosity and the reduction as it gains temperature. The colder, thicker oil has a damping effect on the parts generating the noise.
    It might be in the bearings, but might also be a slider rattling on a hub, the sliders are unsupported in neutral, spinning quite loosely in the shift forks. As you depress the clutch, the input shaft stops spinning and the 3rd/4th slider - partially above the static oil level, will stop turning and rattling.
    It could be the thrust bearing on the input shaft is a little worn, disengaging the clutch puts a slight preload on this bearing, controlling the end float, this might eliminate the noise.
    Best way to test this is to partially load the clutch pedal, but do not fully depress, which would stop the shaft and eliminate the noise anyway.
    As you add weight to the clutch pedal, the unclamping of the clutch friction disc causes it to begin sliding on the input shaft. This will move the shaft just enough to change the noise, check that out, hot and cold.

    Typically a 915 rebuild with a high new parts count will easily eclipse $3K for parts, of which nearly $1100 can be bearings if you replace everything (including needle rollers under the idler gears) Driver teeth at $100 / gear x 5, Sliders $125 each x 2, Synchro rings $40 each x 5, Slider hubs $225 (ish) each x 2, 5th /Rev slider and slider hub approx $750, etc, etc.

    Most 915's are rebuilt with mostly used parts, new or old parts I can not do it properly in less than 8 hours including a CWP set-up.
    But I'm not the fastest guy out there.....

    Regards

    Hayden
    Technical Director
    Windrush Evolutions Inc.

  5. #5
    Blessed be the lowered RickS's Avatar
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    Guys, thanks for the responses. I will try your suggestions, while keeping my fingers firmly crossed.

    Rick
    71 914 3.0, 82 SC, ESR 376, RG 307

    "The problem with the world is, the ignorant are cock-sure and the intelligent are full of doubt." Bertram Russell

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