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Rearend seal

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Robin, Jan 25, 2002.

  1. Robin

    Robin 1/2 ton status

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    I have a leak in the rearend where the driveshaft attaches. According to the service manual, replacing that seal is not trivial (special tools, checking torque, etc.)

    Is it really all that, or is the book just trying to scare me off.

    72 Blazer; Disassembled for restoration; 383/350
     
  2. Triaged

    Triaged 1/2 ton status

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    It is kinda a pain. You have to remove the pinion gear to change it out that get the right bearing preload back into it. How bad does it leak?

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
    <a target="_blank" href=http://community.webshots.com/user/triaged>See it Here </a>
     
  3. skyblazer

    skyblazer 1/2 ton status

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    I changed out my pinion seal and reset the mesh on the ring and pinion with shims at the same time. Not to expensive, BUT, I just noticed that I have play in the pinion (forward and aft) and that is definately not good. I probably overdid the bearing preload on the pinion and squashed the crush sleeve. I plan to go to a drivetrain place this week to have it profesionaly done ($165 + parts) before the whole thing falls apart. I should have done that in the first place.
     
  4. Steve_Chin

    Steve_Chin 1/2 ton status

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    Here's the scoop on this. If you are not changing out the bearings, you don't need to re-check torque or anything. What you *definitely* need to do is mark the pinion stem, the pinion yoke, and the locking nut so that you obtain the same pressure on the crush sleeve that was there originally. Mark them very precisely and when you remove the nut make note of exactly how many turns it takes to remove it. Then you just pop the seal, drive in a new one, and reinstall the pinion yoke and nut, re-stake the nut, and you're off.
     
  5. Robin

    Robin 1/2 ton status

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    Thanks Steve, I got the new seal in and tried this with a new nut and washer which of course didn't go back together with the same number of revolutions, but it leaves me with a question:
    1) When I tighten the bolt, isn't the clearance of the front bearing dependent on the length of the crush sleeve?
    2) Doesn't the torque on the nut really effect the loading on that front bearing?
    3) When I tighten the bolt (say 30ft/lbs) the pionon yoke still has about .01in end play and when pulled out as far as it will go, about .01in. side play. Is this normal?

    So I'm wondering what effect the torque on the yoke nut has to do with the differential engaging properly when it seems that the all it does is keep the front bearing in place. The real depth of the pinion shaft seems to be set by the length of the crush sleeve...

    The side play is really a function of how deep the front bearing sits in it's race, which in my case seems a little sloppy, but that's where the crush sleeve holds it...

    72 Blazer; Disassembled for restoration; 383/350
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    Robin, the pinion depth should be set with shims and the bearing clearance/preload by the amount of torque on the pinion nut (load on the crush sleeve).

    0.01" end play (thrust clearance) is excessive by an order of magnitude. It should be much lower than that. Side play (runout) is an unfortunate side-effect of tapered bearings, but should be manageable if the thrust clearance is brought down.

    I'm kind of at a loss here because ther was no way to tell where to set the pinion preload unless you pull the axles and differential and then adjust the pinion nut until the bearing preload gets to ~15 lbs.*in.
     
  7. Robin

    Robin 1/2 ton status

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    So even then, the nut in question has a taper at the end, which makes the torque a dependency on the nut taper, not thread stretch due to force against the bearing...

    So how does my thrust clearance get too great when the nut is tight? You'd think that wear would cause the clearance to be too tight?

    72 Blazer; Disassembled for restoration; 383/350
     
  8. skyblazer

    skyblazer 1/2 ton status

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    Robin, first of all I'm not an expert on this (I screwed mine up), but I think that the torque spec for bearing preload (15 lbs. in.) is not the torque on the bolt but the torque of the pinion and bearing rotating assembly. The nut is tightened against the crush sleeve until drag of the pinion and bearing is 15. I overdid mine and ran it that way for just a few miles and took out the ring and pinion because the mesh wasn't right.....not good.

    <font color=blue>As my truck gets higher my balance gets lower!<font color=blue>[​IMG] <font color=red><a target="_blank" href=http://coloradok5.com/gallery/albuo72>PICS</a></font color=red>
     
  9. Steve_Chin

    Steve_Chin 1/2 ton status

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    Skyblazer has it right. Squash the crush sleeve until you have zero end-play, then tighten the nut some more until you have the prescribed preload on the pinion bearings. The problem is, the factory only lists a preload for the bearings with the ring gear not installed in the setup.
     
  10. Robin

    Robin 1/2 ton status

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    It all becomes clear now (the torque of the spinning mass vs. the torque on the bolt)! Thanks for your patence guys, in getting through my thick skull...

    So if this is the case, it was way too loose before I replaced the seal. So if I was to err on the conservative side, should it be tighter or looser?
     
  11. Steve_Chin

    Steve_Chin 1/2 ton status

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    Robin, it needs to be a lot tighter than it is now. Keep tightening it until you get no end-play, then tighten it a little bit more until you get just a hint of drag on the pinion itself. As I said earlier, it's best done with the differential out so you can set it up for 15 lbs.*in. of drag.
     
  12. Robin

    Robin 1/2 ton status

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    So Skyblazer screwed his up by ???

    If he adjusted the drag with the differential in (ring and pinion installed), wouldn't 15lbs/in be effectively less torque then if there were no gears and axles to have to spin to get to 15lbs/in?

    If he used 15lbs/in with the diff in, then why did it get screwed up?

    I'm willing to go with the "hint of drag" plan, but I guess I'd feel a little better if could use the torque wrench somehow...

    BTW: My front axle feels pretty good at the pinion yoke, could I use it for comparison? (10 bolt original)
    I mean could I expect the drag to be the same for both axles with the differential in?
     
  13. Steve_Chin

    Steve_Chin 1/2 ton status

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    Robin, I wouldn't expect that the front axle's pinion will have the same drag as the rear's because the ring gear is a different diameter, the bearings are different sizes, and the axles are very different. That might get you close, though.

    In answer to the first question, yes. The amount of preload on the bearings would be much less if the nut were tightened to achieve 15 lbs.*in. of drag on the pinion and the differential were in vs. it not being in. You might find that there would not be any preload on the bearings at all, since it very well might take more than that amount of torque to just get the differential moving (depends on how everything else is put together).
     
  14. Robin

    Robin 1/2 ton status

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    Well, I did all I could. With my longest 1/2" socket wrench opposite a huge pipe wrench held by someone else, to hold the yoke, I put all my weight into it and finally got to where there is almost no end play.

    There is no way, without extending the handle of my 24" socket wrench with a piece of pipe, that I could get preload on the bearing. There must have been a lot of play before it took it apart, because the nut came off with ease...

    What do you think? If there is still end-play and I can't tighten the nut any further, I shouldn't be any worse off should I?
    At least the runout is gone...
     
  15. skyblazer

    skyblazer 1/2 ton status

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    Wow, I don't think that you should have needed that much torque to compress the crush sleeve and set up the correct pinion drag. The guy at the shop told me that when you set up the pinion drag you must get the 15 in lbs drag and the he gave the pinion a pop from the gear side to make sure that the pinion bearing and race were meshed together right. Then he reset the drag again because there was still a little play. Anyhoo, it didn't take that much effort to crush the sleeve.
     

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