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Rear end noise?

Discussion in 'The Garage' started by Rolled, Jun 1, 2003.

  1. Rolled

    Rolled 1/2 ton status

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    I have noticed that if I am going 30mph my rear end will start making some loud gear noises when I let my foot off the gas. It gets louder the faster you go. At first I thought it was the third gear in the tranny because it only did it in that gear but on the freeway today I pushed in the clutch at 60mph and sure enough, it started making noise. So it does it coasting over 30mph.

    Some history:

    12 bolt
    3.73
    35's
    465
    208
    New u-joints

    I pulled the yoke off the 12 and put it back on without torquing it back on. Maybe that caused a problem. A couple of the teeth on the ring gear had some pitting but no broken teeth. It also has oil.

    I have never run this gear ratio with such big tires on such a heavy truck so foe all I know this might be normal, but I doubt it.

    What do you pro's think?
     
  2. Confedneck

    Confedneck 3/4 ton status

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    what kind of 12 bolt? posi? limited slip?
     
  3. Rolled

    Rolled 1/2 ton status

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    It is a stock open rear end. Have any ideas? I'm afraid it is going to lock up on me. Any help?

    [I may be wrong]
    Posi and limmited slip is the same thing as far as I know. I think Posi is a name made up by GM that is synonymous with limmited slip.
    [/I may be wrong]
     
  4. TXsizeK5

    TXsizeK5 1/2 ton status

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    Is your T-case dropped?

    I had this noise originally with 5" of lift & dropped tcase but only at 65+mph... then i got 6"-7" of lift and my 14bff axle and it would do it at 40+mph. I got a CV shaft and no more vibes and no more grinding noise when I let off the gas.
    Maybe try and drop your tcase or get a CV shaft or shims for better angles.

    And yes, posi & lim slip are bassically the same thing. They're synonymous
     
  5. Rolled

    Rolled 1/2 ton status

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    I was thinking of getting a cv. I had a burb dl cut down a couple months ago and now wish I went with the cv. I am thinking if going 14sf when I convert to the th400. I will need to do some driveline work if I do that so I will go with the cv.

    I guess I'll try some degree shimms. Anybody know where to get them? Also, what about regular lift shimms? My frame is a bit bent and I need to pick up the front drivers side and inch to make the rig sit level.



    Anybody else care to speculate on what my chattering gear problem might be?
     
  6. Rolled

    Rolled 1/2 ton status

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    No the T-Case is not dropped. My driveline is at a steep angle but everybody says a 4 inch lift is nothing and the angle is OK.
     
  7. Blue85

    Blue85 Troll Premium Member

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    In my mind you answered your own question: [ QUOTE ]
    I pulled the yoke off the 12 and put it back on without torquing it back on

    [/ QUOTE ] When a pinion nut gets loose (the nut that holds the yoke on), the gearset will still drive OK forward, but when it is back-driven, the backlash goes all wrong and a rotten grinding noise is heard.

    Make sure the pinion nut is tight. I've had that problem before with my old 10-bolt rear. You are really supposed to use a new nut every time you take an old one off. However, many people do OK just be re-tourquing the old one and staking it again.
     
  8. Rolled

    Rolled 1/2 ton status

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    The nut is very tight. I used a half inch impact wrench putting it on. I know that is not the right way but I did it anyways /forums/images/graemlins/wink.gif I am going to retorque it in the morning and see if it goes away.

    However, I am now thinking it is the tranny again. My above assumtion of it being the rear since I pushed the clutch in, and it still made noise, has flaws since the driveline is also turning the tranny. Also, I can replicate the chatter if I am going over 30 (my speedo is off, more like 35 - 40) and I move the shifter almost all the way into 2nd.

    I'll look at again in the morning but I think I am just going to swap out the 465 for a th400. I was going to do that anyways. If that does not work I will throw in a 14sf in place of the 12. And if that does not solve the problem I'll throw some cash into something else, and so on /forums/images/graemlins/smile.gif
     
  9. Blue85

    Blue85 Troll Premium Member

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    OK, so did you check the U-joints yet?
     
  10. Rolled

    Rolled 1/2 ton status

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    I have not checked them but I have two new drivelines with less that a couple hundred miles on them. They better be good /forums/images/graemlins/wink.gif
     
  11. Rolled

    Rolled 1/2 ton status

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    Here is another possibility -

    What about the transfer case chain? I don't know much about them but I can turn the rear drive line back and forth more than I think I should. If you put a mark at 12:00 and turned it by hand it will turn to the 12:30 position while it is in 1st gear and the tcase is in 4hi. With the tranny in neutral (checking slop in rear) it will turn to the 1:00 position.

    Does that sound right?

    Also - I had the tcase apart the other day fixing leaks and the chaun had about .75 to 1 inch of slop to it. Maybe thats OK for a tcase but I know a timing chain would not work that loose. I know, apples and oranges but I am still learning related 4wd part specs.


    So, what do you all think about the tcase rattling when I take my foot off the gas?
     
  12. Don

    Don 1/2 ton status

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    If the chain were slipping, it would make noise, both forward, and rearward. My bet is the pinion nut/crushsleeve combo, are loose. /forums/images/graemlins/eek.gif
     
  13. Blue85

    Blue85 Troll Premium Member

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    My opinion has not changed. You need to be looking at your pinion and U-joints, not the T-case and tranny. Good Luck
     
  14. Rolled

    Rolled 1/2 ton status

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    The ujoints are brand new and I checked them last night so I know they are good but the pinion nut is still at an unknown torque. I'll be crawling under the rig tonight to recheck the rear.

    Anybody know the torque spec for the pinion nut? I'll do a search right now to see if I can find it but if anybody wants to throw me a bone I'll appreciate it.
     
  15. Rolled

    Rolled 1/2 ton status

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    I put a sound scope on the tranny, tcase, and the rear. Tranny was quiet as a mouse, rear sounded like a Harley, and the tcase sounded like a Harley look-a-like.

    I since took off the rear driveline and went for a ride. Now everything is nice and quiet. I suspect it is the rear but let me ask this:

    Is there anything inside the tcase that could make noise but might go away when the d-line is removed? My guess is no but I would like to 100% eliminate the tcase as a potential source before I buy a new rear.
     

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