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8.5 diff tear down and rebuild

Discussion in 'Engine & Drivetrain' started by Matthew Jeschke, Sep 24, 2018.

  1. Erickk120

    Erickk120 Full Access Member

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    I feel bad for you, the odds of not one but both sons of b#$ to fail on you, that truck has a deathwish. I don't mind tackling a rear end since those are fairly straightforward. Now an 8.25 I would just cry and would just get a used one, those look like a royal pain in the butt to do. my hats off to you for even touching those ugly f#$rs. GL!
     
  2. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    I just rebuild the axle tube on the 8.25 it was super simple other than... NO SPECS online lol And spacers needed setup. Thank GOD for this forum. Somebody gave me the specs from a service manual.

    I'm assuming the rear end will be even easier. However, first challenge. Where to put the axle stands. I put them just in front of the rear lower control arm bracket. Not so good, car likes to almost tip back there. Honestly, I'm not 100% sure where is ideal to put these axle stands other than... the rear end lol
     
  3. Erickk120

    Erickk120 Full Access Member

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    For the one I did out of the car it was easier, those 10 bolts are easy to remove and install. For the ones I did in jackstands I placed a big 6 ton jack stand in each side of the axle in between the shockmount and the spring perch trying to distribute the weight into the springs. Plus 2 extra ones in the frame just in case with the wheels choked. There is plenty of room once the spare is off with panhard bracket along with the sway bar bushings unbolted. I had a big piece of cardboard under to limit bearing contamination on final set up with the real bearings.
     
  4. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    First, do they make a cap that you can put on the break line when you disassemble the system? I need to disconnect that T above the diff to pull it out. And I don't want to loose my fluid, I literally JUST flushed the brakes lol

    So I found another Diff at the junkyard. It's identical minus possibly the locker / posi-traction. Called dealer and they told me it was an open diff. However, GMpartsdirect.com says it's a limited slip. Go figure. The glove box options were missing in the junk car but I did snag it's VIN. 1GNEK13T21R140793 My VIN is: 1GNEK13TX1R201680

    Seems a bit odd they would build a 4x4 Tahoe (as the junkyard truck was) and put in an open diff?

    I'm going to open the case this evening and will find out soon enough.
     
  5. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    Rusty diff, must have came from up north :/

    That's the location I'm wondering if there is a cap for? The car side of that connection.

    20180925_144035.jpg 20180925_144451.jpg
     
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  6. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    Okay so I got the junkyard diff opened up. Definitely an open diff :/ I'm pretty sure I can reuse the pinion and ring gear, as well as spider gears (if they fit in my positraction). The gears look literally like new, and this one was regularly maintained the fluid was a bit dirty but didn't have any particles in it. I think I will cannibalise it. and rebuild mine as it's a posi-traction and housing isn't all rusted up. However, I need master overhaul kits with bearings and what ever is inside the posi-traction housing (I'll rebuild that too).

    Anybody know where to get that stuff (preferably timken bearings).
     
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  7. swathdiver

    swathdiver Full Access Member

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  8. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    I was looking at that, but says it doesn't fit my truck. When I click what does it says it's for an 8.6 Diff... So now I'm a bit confused. I look up my VIN number on GM Parts Direct and it's not clear on if it's an 8.5 or 8.6 diff.

    My Rear end on GM Parts Direct, 3.73 w/ limited slip option

    On a sad note, I just noticed I will be unable to reuse the spider gears inside the diff housing :( They are different on the open diff. Hopefully mine aren't destroyed.
     
  9. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    I figured it out. The 8.5" was discontinued in 1999 it had drum brakes, and a few other differences. Even so many of the parts are inter changeable. After 1999 everything went to 8.625 so I'm good.
     
  10. Matthew Jeschke

    Matthew Jeschke Full Access Member

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    I got the rear end out. Getting ready to swap the junkyard one in. I'll first tear down the blown one then start rebuilding it.

    Watching this video, is STUPID helpful... crazy helpful but doesn't have specs for 8.6 / 8.5 diffs.

    I also need to learn how to inspect the carrier unit... The posi-traction stuff.



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