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Slack in rear end

Discussion in '2013-14 Shelby GT500' started by Derek5774, Aug 31, 2013.

  1. Derek5774

    Derek5774 New Member Established Member

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    Has anyone ever noticed extra slack in rear end?
    By slack I mean that the driveshaft is able to turn a quite a bit before the wheels start to turn.
    I know that there is supposed to be about a quarter inch of play but I'm seeing more than that?
    And it is not the universal joint
    A noticeable sound is made as the slack is picked up to turn the wheels.
    Has anyone had this problem or know the cause??
    I'm trying to figure out if I ordered the right parts to fix it. Haven't had time to pull the diff cover yet.
     
  2. Bad Company

    Bad Company Well-Known Member Established Member

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    That is the backlash adjustment between the ring and pinion gear. There is no way to fix it if this gear set has more then a couple of hundred miles on them. If you adjust the backlash tighter with an established wear pattern on the gear surfaces then the rear end will whiiiiiiine
     
  3. raustin0017

    raustin0017 Well-Known Member Established Member

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    Mine only has 560 miles on it so far. At about 300 I was under the car and did grab the DS and tried to turn it. Did not have any noticeable 'slack' in the system. It seemed very solid to me.
     
  4. Derek5774

    Derek5774 New Member Established Member

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    I ordered new gears, differential, and threw some moser axels in the order
    Kit comes withe bearings and other needed supplies

    This is like a full rear end rebuild,
    Think this could correct the problem??
     
  5. SteveWK

    SteveWK Active Member Established Member

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    Mine has done the same thing since day one, and like you I was concerned. Several track days and 10k miles later I have no problems or whine. I don't hear it unless the windows are down and it doesn't happen that often. I've also noticed what I think are the clutch disks coming together when I engage the clutch. It sounds similar to metal plates coming together, a metallic clink type of sound. Probably a product of the dual clutch disks, and again I haven't had any problems with my clutch.

    Steve
     
  6. Bad Company

    Bad Company Well-Known Member Established Member

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    Setting backlash really depends on the particular gear set you have as to whether it will be on the tight side of the tolerances or the loose side of the tolerances with the correct wear pattern on the gear surfaces. A new gear set may not make a bit of difference in this in your case, unless your old set was set too loose to begin with from the factory, but didn't whine from being too loose. To correct this problem and run a tighter backlash you may have to try a few different sets of ring and pinion gears. Never take two sets of gears and mix and match the ring and pinions to try to achieve a tight backlash setting. The gear manufacturers match the ring and pinion gears in a set based off of measuring them. To mix and match gears from two different sets is an invitation to problems

    When you remove all of the rear suspension bushings and replace them with spherical bearings, then you start to feel and hear the backlash setting throughout the car as you transition On/Off the throttle while cruising. This is a normal byproduct of these types of suspension modifications.

    Derek from what I remember of spinning my own driveshaft while under my car, Ford does have a considerable amount of backlash in these rears. Unless you're changing gear ratios at the same time, I wouldn't tear this rear apart if the wear pattern on the gears is normal and it doesn't whine.
     
    Last edited: Sep 1, 2013
  7. raustin0017

    raustin0017 Well-Known Member Established Member

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    I got a silly question. Why not have this addressed at the dealer...it is under warrantee correct?

     
  8. Myfast70

    Myfast70 Active Member Established Member

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    I think the car has been pretty modified already.
     
  9. Devious_Snake

    Devious_Snake PSR Major! Established Member

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    Dealer won't do squat anyway....mine has the same kind of slack. Has had it since the get go. I am going the same route as Derek and building the rear in the future
     
  10. dubbsfaris

    dubbsfaris Shelby SP Region Director Established Member

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    One thing I really liked about my 2008, when the clutch began to engage, the sound it made was very similar to a snake hiss. The 2014 doesn't do that at all, but it feels better.
     
  11. Derek5774

    Derek5774 New Member Established Member

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    You are right
    Dealers see a kenne bell and that is their first excuse to charge me for stock parts
    When paying, I always build it stronger

    The car did not have this much slack at some point, I know that for sure.
    To me this is abnormal.
    I will soon pull the rear dif cover to check oil and see if I notice anything Wrong.
    Thanks for every one's input!
    Has anyone else seen this issue??
     
  12. Tob

    Tob Salut! Staff Member Super Moderator

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    Derek, there is much more than 1/4" of "slack" as you call it with most any RWD car, including ours. Fractional tolerances at the gear mesh level are amplified by the time it gets to rotating the OD of the driveshaft.
     
  13. Derek5774

    Derek5774 New Member Established Member

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    Maybe there is, I'm not sure exactly how much is normal
    What I do know is that mine has quite a bit more than normal and there is not supposed to be a clanking noise as the slack is picked up before the wheels turn
    Question is, what would cause this?
     
  14. Bad Company

    Bad Company Well-Known Member Established Member

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    Derek, make sure you inspect the gear wear pattern and backlash before you disassemble anything. These rears have quite a bit of backlash in them that gets amplified when you do suspension mods to the rear of the car that eliminate the bushings.

    My own car with spherical bearings on the LCAs and a solidly mounted Torque Arm at the rear mount with a Delrin sliding bushing at the front mount, has a ton of noise and thumping coming into the cabin from bouncing on the backlash of the gears that I consider perfectly normal for my modifications.
     
  15. Derek5774

    Derek5774 New Member Established Member

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    I do have full BMR rear suspension
    But if I have to live with this amount of noise
    Then I will remove it all

    Is there any other solution?
    Can changing the pinion angle back to stock help??
     
  16. Tob

    Tob Salut! Staff Member Super Moderator

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    Which BMR upper do you have?
     
  17. Derek5774

    Derek5774 New Member Established Member

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    it has BMR adjustable upper and lower control arms
     
  18. Bad Company

    Bad Company Well-Known Member Established Member

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    The rear axle can make different types of noises, whether it has a mechanical problem or not. Pinion angles will usually cause a rumble and driveshaft vibration that is heard and felt at high speeds, if they are too far off of spec. This usually gets worse as speed increases, but it may actually smooth out somewhat after you pass through the worst part of it as speed continues to go higher. This is because it is a harmonic that will resonate more at certain speeds than others. From what you have said that you have done to the car and your complaint, I doubt the pinion angle is the problem

    Any type of bearing problem will usually admit a rumble and harmonic. This rumble/harmonic again will increase and decrease as speed goes up and down. A bearing going bad on either the pinion gear or a carrier bearing will increase the backlash above spec. I would think you would also be complaining about the bearing noise increasing at the same time in your posts though. Also as the bearing tolerances become looser from the failing bearing, you will start to feel a harmonic vibration that will follow the noise changes at higher speeds. Failing bearings will usually change the sounds and vibrations they are admitting as you apply engine torque or float the driveline to the rear at a constant road speed where the rumble/harmonics are the worst.
     
  19. Tob

    Tob Salut! Staff Member Super Moderator

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    Derek, I meant are you using the upper with a spherical or poly?
     
  20. Derek5774

    Derek5774 New Member Established Member

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    I believe it is Poly


    I pulled the diff cover and there is no extra slack between the drive shaft and gears
    the extra slack is between the differential and axles
    I was told by a few that this is normal and the suspension mods might have made it more noticeable. I'm not sure that is what it is, just a guess at this point. Since there was an oil leak, I was concerned and opened it to check.
    Installed a new differential cover to stop the leak, dealer had resealed it twice before and no luck.
    I am upgrading the axles and differential in the near future and I will know for sure if there is any damage when they pull the stock axles out.
    Since everything looked ok and I know that the differential has oil in it, I will go drive it a bit and if there is a problem, Something should break.
     

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