8 3/4 gear pattern

Fuselage Years

  1. TNT440

    TNT440 Member

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    Setting up gears for my 71 New Yorker 489 case. New gears, bearings and races. I am new at this so I am asking for opinions and looking for any helpful advise. I have the differential assembled with a test pinion bearing for easy shim adjustments. Pinion depth was set using ratech tool. Will be installing crush sleeve eliminator but it is not currently installed, so no preload established yet. Seal is not installed. Backlash is set at .008". Pattern doesn't look terrible but I was wondering if I should add .010 shim to get it a little deeper. Also thought I might lose a bit more depth when establishing pre-load. Thoughts?
    20210822_114613.jpg 20210822_114632.jpg 20210822_115506.jpg
     
  2. 70bigblockdodge

    70bigblockdodge Old Man with a Hat

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    New gears I would set tighter backlash for wear/break-in.
    The coast looks good, IMO I would try to get the drive pattern more toward center/deeper of the ring tooth.
    Disclaimer: I am not even remotely a expert on these.
    Now that I am looking I might have that backwards. The drive may be spot on and coast on heal. In which case I would leave it.
    So in reality I'm not helping at all.
     
    Last edited: Aug 22, 2021
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  3. WOT440

    WOT440 Member

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  4. bigmoparjeff

    bigmoparjeff Senior Member

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    I installed a set of 3.91's in an 8-3/4 last year. I watched a lot of videos on YouTube, and ended up following the advice in this one.



    I think he would tell you to go a bit deeper on your pattern.

    Preloading the bearings may affect the pattern a bit. Installing your non-set up bearings may affect the pattern too. On mine, it seemed like everything I did changed the pattern. I bought one of the $100 pinion depth tools and it was just about useless.

    The gears are noisier that I would like, not terrible, but noticeable. The first paragraph in the instructions basically stated that the gears were likely to be louder than stock and tough luck if you don't like it. This was disappointing for an expensive set of US made gears.

    Jeff
     
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  5. TNT440

    TNT440 Member

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    Thanks everyone, I ended up reaching out to Cass at Doctordiff. I bought the gears from him so I sent him some photos, he responded right away and pointed me in the right direction. Great guy to deal with.
     
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  6. bigmoparjeff

    bigmoparjeff Senior Member

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    I'm curious.

    What was his advice when he saw your pattern?

    Jeff
     
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  7. TNT440

    TNT440 Member

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    He said it was close but thought the pinion could go a little deeper. He suggested adding .002" shim. He said to check pattern and backlash every 90 degrees. I did that and sent photos of drive and coast for each of the 4 locations. He said if the pattern was consistent with .008" backlash the depth looked good. Here are a couple examples 20210823_214912.jpg 20210823_215007.jpg
     
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