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Whine and chatter - 12 bolt Moser Rear

This is a discussion on Whine and chatter - 12 bolt Moser Rear within the Drivetrain forums, part of the LSx Technical Help Section category; What's up folks- I stuck a used moser 12 bolt with eaton posi, 33 spline axles, and 373's on my ...

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    1998 Pontiac Transam WS6

    Whine and chatter - 12 bolt Moser Rear

    What's up folks-
    I stuck a used moser 12 bolt with eaton posi, 33 spline axles, and 373's on my ws6. It was a bit noisy on install so I agreed with the shop to have a rebuild done. (they thought it might be a bad bearing). They did a rebuild and I'm still experiencing noise. I did some research and found out that these Moser 12 bolts have a tendency to make noise. The rear is definetaly strong and the car drives ok but it has a slight whine around 50mph (not a big deal), but what is annoying is on take off (slow speeds) both forward and reverse, it makes an annoying chatter. Drives fine and everything but kinda loud and annoying especially considering how much money I've spent when all was said and done. Could this be as simple as having maybe put in the wrong type of fluid in the rear? Or do I have a bigger problem? Thanks

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    Spaz is My Mentor SMWS6TA's Avatar
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    Did they check pinon spacing and gear engagement pattern? Backlash?

    Could even be the pinion nut is on too tight.

    When my 8.8 was getting assemble I found out that there is some considerable room they can set it too.
    Last edited by SMWS6TA; 06-20-2014 at 10:46 AM.

  3. #3
    Moderator Firebirdjones's Avatar
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    The Eaton posi units need a limited slip additive to work properly. That sounds to me what your chatter might be. Very common with clutch style posi units.

    Also they don't like synthetic fluids so hopefully your shop didn't put that in there.

  4. #4
    Spaz is My Mentor SMWS6TA's Avatar
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    FBJ, I used synthetic fluid plus the additive in the 8.8, will this be an issue?

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    Moderator Firebirdjones's Avatar
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    If you are still running the stock clutch style posi that the 8.8's originally had (they are basically a 12 bolt) it's generally not recommended to run synthetic with those. Clutches don't operate properly. I'm guilty of running synthetic in them years ago with no ill affects, but I don't practice that anymore.

    I've even tried synthetic in them because the bottles claim they already have the limited slip additive, but got severe chatter anyway until a bottle of additive was dumped in. So I just stick with a good ole GL-4 rated gear oil for the old stuff and dump a bottle of additive in.

    If you run a locker there are no worries on which oil you choose.

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    Our Moser 12 bolt came with a Truetrac... No clutches. It is a bit noisy, especially with the tunnel mount torque arm. Backlash on ours was a hair over 0.11" if I recall correctly.

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    Moderator Firebirdjones's Avatar
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    Yeah they still give the option of the style posi you prefer. All these tru-tracks and lockers are popular but I still opt for the clutch style stuff. I just like the rebuildability and being able to taylor pre-load on the clutch packs, and it's quiet with no oddball operation on wet roads that you sometimes get with certain lockers. They seem to last me years and years without issue. Some I have here are original GM Eaton units that are 40+ years old, haven't been cracked open and still working perfectly.

    So when I bought the Strange 12 bolt for my wifes car I opted for the Eaton clutch posi unit in that as well.

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    Good news folks. I guess maybe the rear had been sitting a bit before install, or maybe just needed a little time, not sure what but I did a few small burnouts and pounded on it a bit over the last week or so and it seems like the majority (if not almost all) of the chatter is gone! There's still a slight wine sometimes while on the freeway but not a big deal. Keeping my fingers crossed that the chatter stays away though. As strong as this rear is, that chatter (going slow, taking off etc.,) I couldn't help but feel like it made my car sound a little like a clunker, especially after all the money I put into this lol. I read on some other places that this chatter is sometimes due to "tight" clutches or something with the weight of the release spring or something of that sort and maybe after a little hard driving just needed to get it "worked in" a bit (who knows lol). I'll probably double check at some point with the shop that installed it to make sure they didn't use synthetic and that they added the posi additive, but just hoping that the chatter stays away. Woohoo!

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    Good news folks. I've done a few small burnouts and pounded on a rear a bit over the last week or so and it seems most, (if not all) of the chatter is gone. Maybe the rear sat for a while and just needed to be 'worked in' a bit? who knows. Just hope it stays this way. Still has a slight whine around freeway speeds, but not a big deal and what from I read fairly normal/common. I'll check with the shop at some point to make sure they didnt add synthetic and to see if they added the additive or not, but hopefully the chatter stays away.

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    FBJ can probably clarify, but I seem to recall something about finding a large parking lot and driving a "figure 8"...

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