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New rearend issues

Discussion in 'Engine & Drivetrain' started by SRQYukon, Feb 9, 2020.

  1. SRQYukon

    SRQYukon Full Access Member

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    So on Dec. 29 I ordered a remanufactured ATK rearend from JEGS. My old rearend had newer gears but bearings started roaring. Took a while to get it, but the shop finally installed it on Jan. 21. I followed the break-in procedure with several short trips followed by cool-down and then took a road trip for 250 miles to complete minimum 200 mile break-in. I then followed the trailer towing break-in instructions with a few short towing trips. Then I resumed normal use, but avoided long trip towing as advised until after 500 miles. The shop recommended I come in to have the lube changed after break-in. They did that at 484 miles. At around 550 miles I notice a pronounced "chatter" or vibration when making left turns in the morning when the diff was cold. Then it starting doing that when making right turns. I went back to the shop and they added two more vials of limited slip lube. At first it seemed better, but has now resumed the vibration. Once it warms up, there is absolutely no vibration or noise of any kind. Anyone else experience this? I'm just trying to see if I need to initiate a dialog with JEGS about the problem. Just doesn't seem right.
     
    Last edited: Feb 9, 2020
  2. swathdiver

    swathdiver Full Access Member

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    I don't know why they are using limited slip lube. What fluid is in the the differential now?
     
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  3. PNW VietVet

    PNW VietVet Full Access Member

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    First, like James was asking, is it a limited slip rear diff and if so the correct fluid, without the additive, should have been in it to begin with. Second, they added the additive to ATTEMPT to quiet it for sure. The noise may go away after more miles and be good from cold drive to warm up. I would initiate the dialog with JEGS and keep the shop in the loop. I bet they say the same thing about drive it for a while.
     
  4. SRQYukon

    SRQYukon Full Access Member

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    Thanks for the responses. First, I never said it was a noise. Just a vibration. I call feel the chatter but there's nothing audible. Here are the RPOs, GT4 G80. This is a 8.625" 10-bolt 3:73 with the traction control feature. Seems like a hybrid of a true posi-diff. The manual calls for 75w-90 synthetic axle lube GM part#12378261 or equivalent. As I said the shop recommended changing the fluid that it was shipped with after the break-in. I have no idea what type of lube they used when they changed it, but now I'm thinking that they may have put the additive in the unit in error. GM doesn't seem to call for any additive. Maybe just changing to the correct lube will fix it. It's only been about 100 mile since I noticed the chatter and then only when it's cold or cool,I should say (there is no cold in Florida).
     
  5. PNW VietVet

    PNW VietVet Full Access Member

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    You can bet if you feel it there is likely a little noise there but I did reread what you said and you did say FEEL it. My bad. Same RPO as my 2002 Tahoe. Same fluid, GM part #12378261, that I run in mine so should be right unless the shop put some cheaper fluid and just threw in the additive. You did say that added two MORE vials of the additive to try to fix the problem. I would have changed the fluid after break in as well. Smart move to get those sharp edges out of there that wore off the gears during break in. I like where you are going with this. Remove the cover and get all the old fluid out, I used to use, and still do, brake clean to spray in there and wash it all out with. Let it dry and then install cover with your fav thin film of sealer and let sit for 1/2 day to set up and then refill with the GM fluid. Hope it all works.

    I would let JEGS know if you do what you are thinking, before you do it and see if they agree.
     
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  6. SRQYukon

    SRQYukon Full Access Member

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    Just texted the shop owner and he says they used Amsoil full synthetic 75w-90 which he thought was superior to the GM product. However, he just said to bring it in and they'll change it to the GM and see if that solves the problem. We'll see.
     
  7. wjburken

    wjburken Supporting Member

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    Any update on this?
     
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  8. SRQYukon

    SRQYukon Full Access Member

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    Unresolved at this point.
     
  9. rockola1971

    rockola1971 Full Access Member

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    Its well past the time to pull the dif cover and check gear mesh pattern. (This needs to be done by a shop that routinely rebuilds rearends...successfully). Have them document irregular wear or incorrect setup for warranty purposes.
     
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  10. SRQYukon

    SRQYukon Full Access Member

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    Thanks, Mike. It only has 950 miles on it and it seems fine once it's warm. Almost acts like axle thrust from turning is triggering the chatter, but very odd that it does do anything when warm. Tomorrow we're changing the lube again and looking for any evidence in the fluid that comes out. We'll see what we find. Not sure how I'd go about finding a shop that does routine diff rebuilds, but I can ask around.
     

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