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8.8 gear noise question/theory

Discussion in '2013-14 Shelby GT500' started by Husky44, Mar 2, 2014.

  1. Husky44

    Husky44 New Member Established Member

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    Looking for input from those who've run an 8.8 in previous years' high horsepower cars: Was gear noise a problem?

    I've never pushed more than 400hp/torque before, and only have personal experience, but don't recall ever having an issue with gear noise.

    What is your experience? Please chime in with other cars you've had, horsepower/torque ratings, that ran an 8.8, and whether or not you had issues with gear noise?

    I have a theory, and would like to see if others' experience supports it:

    I suspect, based on my last two tear downs, that the problem with the rear end in our cars is related to the larger pinion bearing. Prior to the 13s, I'm not familiar with any other car that ran that pinion bearing. From what I gather, the FRPP aftermarket axle isn't running the larger bearing, and I'm thinking about swapping the whole assembly, to see if that quiets my noise, unless I've just been lucky in the past.

    Not looking to build a full-on drag car, just something that I can hit on the street, and not hear the gears singing on road trips.
     
  2. VNMOUS1

    VNMOUS1 Well-Known Member Established Member

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    Doesn't matter how quiet it is. Nail a few really hard launches and she's singing again. You've just screwed the backlash.
     
  3. biminiLX

    biminiLX never stock Premium Member Established Member

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    I hear ya Husky, it is annoying.
    As we've discussed in the other thread--solid crush washer, cover/girdle, welded tubes/bracing.
    or 9" swap :)
    -J
     
  4. 19COBRA93

    19COBRA93 Tire shredder Established Member

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    I've been doing gear swaps for probably close to 14 years, and it used to be easy. I'll agree with the suggestion that the new pinion bearings might have something to do with it. On a fox or SN, I could nail a perfect gear pattern in 2 hours. . On these newer 8.8's, it's a real job and really takes precision to make it perfect. Even then, it's difficult. For a while now I've suspected the new big pinion bearing of causing the setup problems. Maybe it's a change in how the housings are machined. Whatever it is, it's almost impossible to get a perfect gear pattern. Change the pinion shim from a .028 to a .029 and the gear pattern goes from one extreme to the other. It's just difficult to get it in between. It's gotten to the point of "good enough" is the new "perfect."
     
  5. Snoopy49

    Snoopy49 Well-Known Member Established Member

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    Where is the shim for the pinion depth located, is it between the inner bearing race and the pinion head or is it between the outer bearing race and the axle housing?
     
  6. 19COBRA93

    19COBRA93 Tire shredder Established Member

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    It's between the inner bearing race and pinion head.
     
  7. Mach828

    Mach828 Active Member Established Member

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    I was surprised by how much wear the gears see. I originally set my backlash very tight. After 10k miles and a lot of hard launches, the backlash has loosened up quite a bit.

    A buddy of mine had a shop install his 4.10s, and they were on the looser side of the tolerance. They were quite, but now after a year of wear we are going to have to take it apart and shim it to tighten it up.

    I'd say its better to be on the tight side and deal with some gear whine. If you can hear it whine, just make your exhaust louder. haha
     
  8. 19COBRA93

    19COBRA93 Tire shredder Established Member

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    Most of the factory gears I've removed were on the really loose side on backlash. Like, out of spec loose (.12-.15). Those were the ones that generally didn't make noise. In general, the noisy factory gears were the ones that were on the tight end on backlash (.08-.10). The pinion shim on factory installed gears has been pretty constant at .028-.30, and side shims have been commonly .265-.270.
     
    Last edited: Mar 4, 2014
  9. Snoopy49

    Snoopy49 Well-Known Member Established Member

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    19COBRA93,

    Have you checked the pinion bearing preload on the used gears? How does it compare with with a fresh setup? I am trying to see if the crush sleeve is being further compressed by hard launches or hard driving, which would lower the preload and affect backlash.
     
  10. 19COBRA93

    19COBRA93 Tire shredder Established Member

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    Interesting suggestion. I've never checked preload before taking one apart, but I've never found one to "feel" different than what I would consider normal. I've corrected some sloppy gear jobs that were done by other shops, and I've found some loose pinion nuts from time to time. Those are a quick catch, but I've never suspected the crush sleeve collapsing even more on a launch. I can see that as a possibility though.

    A couple years ago Ford redesigned the crush sleeve to a thicker/more robust design which uses a bigger pinion nut. Maybe they were finding the old design was collapsing under extreme load. Regardless, that doesn't explain why foxes and SN's were so easy to set up, and S197 aren't. Maybe it's a combination of things.
     
  11. usmotox

    usmotox Living the Dream! Established Member

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    Ford F-150 is rumored to be the same pinion size. I know of several of those that failed many threads in the search on here and some good tech stuff from those with failures.
     
  12. Husky44

    Husky44 New Member Established Member

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    My guy didn't check preload before disassembly, but his diagnosis on tearing down my first swap (done by a friend with a couple of decades experience doing drivelines for a living), as well as this install, both cases were that the pinion had "walked", which I understood to mean that the washer had crushed farther, allowing the pinion depth to change. If we tear down again, I'll have him check preload before teardown, to see how much it's changed since he did the install.

    On the first install of my 3.73s, my buddy set backlash to the tight end of the tolerance (which he thought was still too loose!). In both cases, backlash was wayyyy loose on teardown (don't remember numbers, but out of tolerance on the loose side).

    I stated in another thread, but I've read on multiple offroad forums where guys setting up 8.8s got the pinion depth, with the proper preload set, then measured the crush washer, and replaced it with a solid washer/sleeve machined to the same depth, basically preventing further crush (which appears to be a problem).

    I'm not a professional mechanic, or automotive engineer, but all of my professional training tells me that when you have the same defect, on an install by two different qualified people, particularly on equipment that is essentially 25 years old (basic 8.8 rear end setup), with the only significant change being a design change of one component (pinion bearing), directly related to the failed component, then the problem likely lies with the changed component.

    At this point, my next step is dynamat. I'm going to try to muffle the noise coming through the floor, and see if I can live with it. If it gets worse again, I'm debating whether to just swap the whole assembly to the Ford Racing 3.73 setup, which I believe (but will verify) has the smaller pinion bearing of old.

    Does anyone know if the Boss 302s had the larger pinion bearing? Are they having problems with gear noise?
     
    Last edited: Mar 4, 2014
  13. 19COBRA93

    19COBRA93 Tire shredder Established Member

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    Yes, it's an F-150 bearing. The part number is 9L3Z-4630-A, bearing and race assembly. By breakdown, that part number is an '09 F150. But fits multiple years, multiple vehicles.


    The FRPP rear axle assembly, and the Boss rear end will both have the newer style bearing. Everything built '12 and newer will have the new larger bearing. The FRPP axle assemblies are pulled right from the assembly line, they're just a production assembly.
     
    Last edited: Mar 4, 2014
  14. 1320 Junkie

    1320 Junkie Active Member Established Member

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    Great info here...ill check mine when i build the rear next week.
     
  15. Husky44

    Husky44 New Member Established Member

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    Oh. I was under the impression that only the GT500s had the larger bearing. :shrug:
     
  16. 19COBRA93

    19COBRA93 Tire shredder Established Member

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    That's mostly correct. There have been several different pinion bearings over the last several years, and they have been used in both the GT500's and the GT's. They're all interchangeable, except for certain '13 Boss and '13 GT500's, which use a unique bearing (axle tag #'s S215D, S219D -Torsen rear diffs). 07-11 GT500's have a thick spacer behind the outer race in the diff housing, as the bearing is considerably narrower than the prior design. '12 GT500 was another revision with what FRPP calls the "high torque bearing for modified vehicles." And some '13 GT500/Boss was yet another one that's not interchangeable with any prior years. Some of the Mustang GT's from '10-14 would have the same rear end as the GT500, depending on their options, based on axle tag#. It's all very confusing, and there's really no rhyme or rhythm to it.
     
    Last edited: Mar 5, 2014
  17. Beercules

    Beercules Active Member Established Member

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    I had a 2010 gt, people on those forums were saying to switch to the larger bearing to reduce axle whine.
     

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