Rear axle nuts

Discussion in 'GT350 and S550 Technical Forum' started by Wotfun, Apr 20, 2019.

  1. Wotfun

    Wotfun TMO Advanced

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    So, I’m leaving tomorrow morning for a track day at Barber Motorsport Park in Alabama - about an 8 hour drive for me. Changed brake fluid today - complete flush. While putting the wheels back on (thinking I was about done), I realized the driver side rear wheel was wobbly. After pulling everything apart, I discovered the axle nut was loose. (I could turn it with a socket and just my hand on the socket.)

    After a bit of googling, it seems this is a common problem because a Ford decided not to use a cotter pin to prevent the nut backing off. I also searched for torque specs for the nut. All I found (on other forums) was people saying it should be 98 lb ft. But, checking the passenger side, it seemed to have well over 200 lb ft. Setting my torque wrench to 240 lb ft, it clicked quickly without moving the nut. (Btw, my car is a 2017 gt performance package, with 13k miles and about 12 or so 20 min track sessions.)

    What is the correct torque for the rear axle nuts on the s550 mustang gt with pp?
     
  2. gtorpedo

    gtorpedo TMO Advanced

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    It's 98 lb/ft PLUS 45*

    If you are not using a new axle nut (which is called for in the service manual) i've heard of people using red loctite without issue.

    I have several spare (new) axle nuts if you are close to Arlington and need them prior to leaving?
     
  3. Wotfun

    Wotfun TMO Advanced

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    @gtorpedo, I really appreciate the offer. Unfortunately, I’m in in the Roanoke area - about 3:40 southwest of Arlington. So, round trip would add about 7 hours to an 8 hour trip.

    I’ll have to go the red loctite route. 98 lb ft just seems really low. Especially considering ford says the lug nuts should be torqued to 150.

    What does the PLUS 45* mean? Is that just an extra quarter turn after the torque wrench clicks at 98 lb ft?
     
  4. TMSBOSS

    TMSBOSS TMO Addict

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    98 FT/LBS torque PLUS 45 degrees additional turn on nut.
     
  5. JAJ

    JAJ TMO Addict

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    As TMSBOSS said, that's it exactly. I tighten it to 98 ft-lbs, mark it with a sharpie, then use a 2' long breaker bar with three feet of pipe on it. Even with all that it just barely makes the 45 degrees.
     
  6. Wotfun

    Wotfun TMO Advanced

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    Thanks! Very helpful!

    It sounds like the nut and / or axle is s designed to only allow the nut to be tightened to 98 lb ft and the way to monitor it is mark it with a sharpie so I can see if it’s moved.

    Sound right?
     
  7. JAJ

    JAJ TMO Addict

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    No, that's not quite it. It's a two-step process to tighten the nut. First, torque it to 98 ft-lbs. That takes all the slack out of the system. Then put a really long-handled wrench on there and turn the nut another 45 degrees. The marks are so you know when you've turned it 45 degrees. That extra 45 turn stretches the threaded parts so they can't come undone, and the final torque is probably in the 400 ft-lb range.
     
  8. Wotfun

    Wotfun TMO Advanced

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    Ah, that’s why the nut is supposed to be replaced each time. Once it’s stretched to spec ( 45* past 98 lb ft ), it never goes back to its original form (unstretched) and, therefore, cannot be tightened properly since it’s already pre-stretched. Correct?
     
  9. Wotfun

    Wotfun TMO Advanced

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    This has me thinking it might not be safe to do a track event until I can replace that nut and properly tighten it...argh. Learning is expensive.
     
  10. Wotfun

    Wotfun TMO Advanced

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    Is the axle nut a part Ford dealers are likely to have in stock?
     
  11. JAJ

    JAJ TMO Addict

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    Don't overthink it. Take the nut you have and tighten it properly. If it tightens to 45 degrees past 98 ft-lbs, then run your event and replace it later. I've had mine off and back on three times and they're fine. I have a pair of new ones standing by for when I don't like the feel of the tightening process.
     
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  12. JAJ

    JAJ TMO Addict

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    By the way, it didn't occur to me to look move carefully at the original post until this morning, but now that I have, there's one more thing...

    On an S550, a wobbling rear wheel is caused by a worn hub bearing, not a loose half-shaft nut. There's a CV joint on the half-shaft inboard of the hub, so even if the half-shaft spindle is locked to the hub spline by the nut, the CV joint ensures that the hub is free to move. But it's not supposed to move, except when the whole suspension moves, and what stops it from moving otherwise is a nice, tight hub bearing.

    I had this exact problem when I swapped the rear hubs on my GT350 last year. One of the new hubs was defective and when I was tightening things up, I realized that the flange with the wheel studs was wobbling a bit. Since I hadn't tightened up the center nut yet, I did the 98 ft-lbs part to take the slack out, but the hub still moved. It was a brand new OEM hub and the dealer replaced it under the parts warranty with one that didn't wobble, but it was a bit of a surprise to say the least.

    So, if the rear wheel wobbles when the car is in the air, then the hub is worn and should be replaced.
     
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  13. Nvrfinished

    Nvrfinished TMO Advanced

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    Bingo! I had to buy a new LR hub from the dealer last week just two days before my event. I discovered the issue when pulling my car into the garage to do my track alignment. The hub makes a groaning / creaking sound.
     
  14. Wotfun

    Wotfun TMO Advanced

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    I appreciate all the info and will keep the bearing issue in mind. In my case, it was just the axle nut. As noted in my initial post, after I put a socket on the nut I could grasp the socket and turn the nut. Tightening the nut solves the problem.

    I did decide to go to my event at Barber Motorsport and the car’s doing great. (Except that the ac quit and the backup camera quit. But both of those things happened at my last event and resolved themselves magically on my drive home from the track.

    Again, I truly appreciate everyone’s input and advice.
     
  15. JeffV8

    JeffV8 TMO Race

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    My back up camera never works after a track session
     
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  16. Nvrfinished

    Nvrfinished TMO Advanced

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    Same here for the backup camera as well, but it's intermittent. I have no idea why a track session would cause the issue, but it always works after the car has sat for a little while.
     
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  17. JDee

    JDee Ancient Racer

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    My backup camera is dead when I come in off track, then magically recovers by itself. And yesterday I was bedding brakes and the TPMS warning went off said the system wasn't working, never had that happen before. Checked the dash readout and no readings. This morning I checked it and all is fine and the TPs are 32 cold right where Ford says they should be! Go figure.
     
  18. JeffV8

    JeffV8 TMO Race

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    My back up camera on my 16PP and also my friends 15 won’t work after a 20 min track session or some spirited highway driving. I think it’s a sender heating up in transmission. Ford has replaced camera and did downloads and still does it.
     
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  19. Wotfun

    Wotfun TMO Advanced

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    Makes me glad I got the ‘17 before the speedometer and tachometer went to digital displays.

    Btw, both ac and backup camera resolved before I left the track and, my axle nut is still fine - thanks your advice and red loctite.
     
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