Looking for some affirmation (8 3/4 rebuild not successful)

Discussion in 'Transmission and Drivetrain Tech' started by zakimodo, Apr 16, 2018.

  1. zakimodo

    zakimodo Well-Known Member

    Messages:
    351
    Likes Received:
    18
    Joined:
    Dec 11, 2005
    Location:
    Berthoud Colorado
    View My Photos
    Local Time:
    7:07 PM
    Hi All

    Just rebuilt and installed my first 8 3/4. On the test/ break in drive, I noticed a few things.
    Here is what I am working with
    -489 case
    -3.55 gears from Yukon (rebuild kit from them as well)
    -Eaton Tru Trac
    -Ratech crush sleeve eliminator

    1. Under ~60 MPH the gears were quiet (car is noisy but I didn't notice any unusual gear noise. Over this speed and with the car in gear I noticed a humming noise (Felt more like harmonics than anything). If I put the car in neutral to coast it got quiet again

    2. On my return trip, I started to notice a lot of gear whine when coasting to a stop.

    When I set this up, I had a tough time getting the pinion preload set. At first, I could hit preload with only 90Ft lbs of torque on the pinion nut. A thinner shim would all but lock the pinion up at the same torque. I ended up filing an honing down the pinion spacer and was able to get 175 ft/lbs of torque on the pinion nut w/ the correct preload. I left it at this with some blue Loctite. Looking back, I was losing patience with constantly reinstalling the pinion to get this set... All that said, I feel like I screwed up on the preload (nut loosened up or the bearing cups settled). So, am I thinking correctly, is there anything else I should look at once I have a chance to pull the 3rd member out?

    Just for reference, here is my contact pattern after final assembly.

    20180325_133057.jpg

    20180325_133104.jpg
     
  2. TrailBeast

    TrailBeast Slightly Twisted Member

    Messages:
    18,948
    Likes Received:
    5154
    Joined:
    Mar 11, 2011
    Location:
    Arizona
    View My Photos
    Local Time:
    7:07 PM
    Pinion running too deep in the teeth, and needs to be moved away more.
     
    • Agree Agree x 1
    • AJ/FormS

      AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

      Messages:
      14,694
      Likes Received:
      3928
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      View My Photos
      Local Time:
      8:07 PM
      IMO, I think all you gotta do is give it a tad more backlash and watch the pattern climb up the tooth a bit. The pinion depth looks pretty dar n close, but it could use a tiny bit more
      shim, but I mean tiny.So I would increase the backlash first, to the max allowable, and see what happens.On the street you can get away with quite a bit of backlash.
      The spec is .006 to .008, but I've had to run as loose as .012/.013.. Some patterns want what the want. If that concerns you, call the manufacturer
       
      Last edited: Apr 16, 2018
    • pishta

      pishta I know I'm right....

      Messages:
      13,458
      Likes Received:
      3217
      Joined:
      Oct 13, 2004
      Location:
      Tustin, CA
      View My Photos
      Local Time:
      6:07 PM
      what was your backlash with that pattern?
       
    • mderoy340

      mderoy340 Well-Known Member

      Messages:
      1,926
      Likes Received:
      623
      Joined:
      Aug 2, 2012
      Location:
      Melbourne FL
      Local Time:
      9:07 PM
      Best to set the pinion depth to spec scribed on the pinion, then set backlash to gear manufacture spec.
       
    • zakimodo

      zakimodo Well-Known Member

      Messages:
      351
      Likes Received:
      18
      Joined:
      Dec 11, 2005
      Location:
      Berthoud Colorado
      View My Photos
      Local Time:
      7:07 PM
      That was at .007 backlash. I think the Yukon manual spec'd .006 to .010.

      It's interesting you guys bring this up. A local "mopar nut" (best way to describe him) told me that the tightest he will ever go with an 8 3/4 is .010 backlash.
       
    • AJ/FormS

      AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

      Messages:
      14,694
      Likes Received:
      3928
      Joined:
      Jan 19, 2014
      Location:
      South-Central Manitoba,Canada, 900ftelevation
      View My Photos
      Local Time:
      8:07 PM
      I've had no problems at up to .012/.013, in going on 40 years. And that includes the ones I have been abusing with the CFII clutch and splitting gears at WOT with the GVOD.
      But; your results may vary......so
      I'm not gonna tell you to run that loose, cuz I'm not gonna buy you new gears if the teeth start unzipping.
       
      • Like Like x 1
      • john-9

        john-9 Well-Known Member

        Messages:
        104
        Likes Received:
        38
        Joined:
        May 11, 2015
        Location:
        Oldcastle , Ontario
        Local Time:
        8:07 PM
        your pattern looks really good ,,what did you set the preload at should be 20-25 in/lbs with new bearings ,,,, but your thinking is off on the pinion bearing preload set up --- you stated using the solid spacer and a thinner shim locks up the assembly ( which is correct ),, with that situation you would then ADD shim ( increase the thickness ) maybe .002 at a time ,, torque the nut to at least 150 ft/lbs and check the preload ,, by cutting down the spacer you are taking shim out and going the wrong way.
        one other thing to check is the I.D. of the solid spacer at the big end .. sometimes these spacers do not sit down flush on the bearing and have to be opened up at tad ( honed out ) to completely seat flush onto the large pinion bearing.
         
        • Like Like x 1
        • zakimodo

          zakimodo Well-Known Member

          Messages:
          351
          Likes Received:
          18
          Joined:
          Dec 11, 2005
          Location:
          Berthoud Colorado
          View My Photos
          Local Time:
          7:07 PM
          Yeah, I didn't specify that the next shim option up wouldn't get me anywhere near preload (too loose). This is why I shaved the spacer down a little.
           
        • zakimodo

          zakimodo Well-Known Member

          Messages:
          351
          Likes Received:
          18
          Joined:
          Dec 11, 2005
          Location:
          Berthoud Colorado
          View My Photos
          Local Time:
          7:07 PM
          I haven't had a chance to pull the 3rd member back out yet. Hoping I can get it pulled out this weekend.
          The day I installed this I was probably over sensitive to any noise/ vibration. I had to move my car this weekend and figured I would take it for a short cruise just to confirm my symptoms.

          First off, the harmonics I mentioned @ 60 MPH is all from the engine. Going to have to get used to the engine being wound up a bit more with the 3:23 to 3:55 ratio change.
          Outside of this, the rear end was quiet until the diff oil warmed up (again on my return route to home). The gear whine is back, although not near as bad as I had remembered it and is only present at ~40MPH (when coasting and under load). Above or below this speed it's silent.
           
        • zakimodo

          zakimodo Well-Known Member

          Messages:
          351
          Likes Received:
          18
          Joined:
          Dec 11, 2005
          Location:
          Berthoud Colorado
          View My Photos
          Local Time:
          7:07 PM
          Got the 3rd member out tonight. Haven't disassembled anything further at this point.
          I checked the overall rolling resistance, its @ 20 in/lb. Which seems a little light to me.
          Here is the wear pattern from the 20 some odd miles I have on this ring and pinion.

          20180428_183746.jpg

          20180428_183732.jpg

          20180428_183444.jpg

          20180428_183437.jpg
           
        • john-9

          john-9 Well-Known Member

          Messages:
          104
          Likes Received:
          38
          Joined:
          May 11, 2015
          Location:
          Oldcastle , Ontario
          Local Time:
          8:07 PM
          again your pattern looks very good --just get in there to set the preload on the pinion bearings correctly and you should be good --- if by checking the rolling resistance of the complete assembled differential you have only 20 in/lbs you should be more in the range of 50- 70 in/lbs as long as the pinion preload is right as well as carrier bearing preload.
          the shim kit with the solid spacer gives you enough shims to set the preload correctly by adding or taking out shim in .002 increments -- itsa mix and match process and can be tedious . you should not have had to shave down the solid spacer for this to happen.---
           
        • Alaskan_TA

          Alaskan_TA Well-Known Member

          Messages:
          3,983
          Likes Received:
          1682
          Joined:
          Nov 12, 2004
          Location:
          PA
          Local Time:
          9:07 PM
          The residual lube showing in your two bottom photos looks very thin, what was in it?
           
        • zakimodo

          zakimodo Well-Known Member

          Messages:
          351
          Likes Received:
          18
          Joined:
          Dec 11, 2005
          Location:
          Berthoud Colorado
          View My Photos
          Local Time:
          7:07 PM
          Just regular ole Valvoline 80-90. The stuff without friction modifier. That picture was taken after a quick blast of brake clean.


          I took the carrier out and found that my pinion preload was ~7 in lbs. Wondering if I had a bearing that I didn't quite get seated as the nut had not moved. I was able to re torque the pinion nut to get the preload back into spec. After that I re installed the carrier and set by backlash to .010. Checked the pattern, its basically identical to my previous pattern. Pinion and carrier together was running @ 60 in/lbs.

          Took the car back out this afternoon, the whine is still there:mad:. It comes in @ ~45mph and is gone by 50. Outside of this you cant hear the rear gears at all.