Advise needed on broken posi

Discussion in 'Transmission & Driveline Topics' started by BC_Homegrown, Apr 4, 2021.

  1. BC_Homegrown

    BC_Homegrown Member

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    So I took the rear end out of the car, marked the ring gear, applied pressure while turning 2 revolutions both ways. This is what I ended up with:
    4.jpg
    2.jpg 3.jpg
    Looks like the one side is ok but not the other, being so low on the teeth would indicate incorrect pinion depth?
     
  2. big gear head

    big gear head Veteran Member

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    Doesn't look too bad to me.
     
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  3. Rosster

    Rosster Veteran Member Gold Member

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    I thought he was going with new diff and gears?
     
  4. BC_Homegrown

    BC_Homegrown Member

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    Still undecided, but I'm leaning towards all new internals installed and setup by a shop. Another alternative would be to attempt to install the new posi unit myself and if I hear any noise then take it to the shop for full rebuild.
     
  5. Fbird

    Fbird Veteran Member Lifetime Gold Member

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    not bad for run gears.....have you been able to get a backlash number yet? It is kinda "touchy feely" process. Also note: it is wise to measure backlash in 2 or 3 different locations as it is common to have a RANGE of numbers example: .009, .011, .010. ....perfectly common. Should NOT be .007, .012, .013???? you should only have about .001-.002 'ish ...difference in readings.
    If you can tear down a rearend.........YOU CAN BUILD ONE!!! With the support of folks here at NASTY....the pic quality, and resources....it's not a voodoo thing! Only a couple special tools required.
     
  6. BC_Homegrown

    BC_Homegrown Member

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    I am still waiting for the indicator gauge unfortunately, but thanks Fbird I'll measure it in multiple spots.

    I would really like to learn, it seems to be a pretty common thing to redo a rear end and having people on here willing to help is awesome!
     
  7. BC_Homegrown

    BC_Homegrown Member

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    Hey guys, finally got the gauge today made some backlash measurements in 10 different spots:

    12
    14
    15
    15
    14
    17
    16
    14
    15
    15

    average of 14.7 not sure if that's in spec?

    Another thing I noticed was the pinion preload is almost non existent, there is no play in it up and down/ in or out but it does spin with very little effort. Not sure if that's normal on used gears?
     
  8. big gear head

    big gear head Veteran Member

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    Wow, that's all over the place. Are you sure that you were holding the pinion completely still? If it moves the very slightest amount then the backlash reading will be completely off. If it's got aa lot of miles on it then the bearing preload will go away. Maybe a complete rebuild would be a good idea.
     
  9. BC_Homegrown

    BC_Homegrown Member

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    I was holding the pinion in my knees and moving the gear back and forth, the gauge was a digital with magnet base. I guess I may could have moved the pinion a bit but it did seem fairly consistent around 15 thou. The gauge probably isnt the best quality either.

    Yeah I'm thinking you're right, it seems the consensus is full rebuild that's what I'll have to do (or get done). Might set me back a bit but worth it in the long run.

    Thanks a bunch for everybody's input, quite the learning curve this hotrod business! Not to mention pricey hah
     
  10. BC_Homegrown

    BC_Homegrown Member

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    Update for those that are interested;
    -was not going to give up quite yet so I borrowed a better dial gauge and secured the yoke alot better.
    -remeasured backlash and it came out to be 11-12 thou, good solid measurements this time, no bouncing around
    -decided to install the truetrac because it and the bearings showed up and was just sitting there lookin pretty
    -removed old differential
    -cleaned out case and found the missing teeth stuck in the groove behind the drivers side bearing (pic)
    7.jpg
    -had a real good look at pinion and ring gear, could not see any chips or damage, think I may have got lucky
    -installed ring gear to truetrac , locktited and torqued bolts in a wheel pattern to 65 ft/lbs
    -installed new bearings to carrier
    -installed carrier, tried using old shims, didn't work, gear was tight against pinion
    -used the .225 shim on driver side like Big Gear Head's post said to do(duh) and then added shims to passenger side until I got the backlash to 12-13 thou. , that was as close as I could get to 11. Carrier was nice and tight in the case. That shim kit worked great.
    -checked the pattern again:
    old
    2.jpg

    new
    5.jpg
    old
    4.jpg
    new
    6.jpg
    -I think it looks similar to before, the coast side is a little wonky but will have to wait to see if it makes noise.
    -torqued the bearing caps to 60 ft/lbs, rechecked backlash and looks good.

    When I get the car on the road I'll know if it's going to require a full rebuild and I'll cross that bridge when I get there. This should enable me to move it out of the garage at any rate.

    Thanks again everyone for all the help, and especially Big Gear Head for the coaching!

    Once I get the axles installed I'll put in 80-90 non synthetic. One thing I'm wondering is the instructions for the truetrac do not mention a limited slip additive, and no mention of break in, is that just for clutch LSDs?
     

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