Drivetrain Diagnosing Rear End Noise - A Couple Of Questions

Discussion in 'SN95 4.6L Mustang Tech' started by spitty70, Sep 23, 2013.

  1. I am trying to diagnose a whirring or whining noise coming from the rear end of my ’03 GT. I did a lot of searching in here and on the web, but I had a couple of questions that I could not find the answer to.

    First a little background on the car: The car has 85k miles on it and is driven on a regular basis, although not daily. I had the carrier and pinion bearings replaced by a pro mechanic about 12k miles ago, so I do not suspect those are the issue, at least I hope not. The diff is the original that came with the car. I also do not have any leaks coming from the differential, or from anywhere else. I usually hear the noise at about 45 mph upwards, and it is most noticeable on the highway. It’s pretty constant and does not really change pitch with when I give some gas or on deceleration. No change in the noise that I have noticed when turning. I have not done the rear brakes or wheel bearings.

    I jacked up the car last night and noticed some in and out play in both of the rear wheels. The passenger side had more play than the driver’s side. Is that type of play normal?

    I tried to wobble the wheels too, by pushing on top and pulling on the bottom of the wheel, but they felt pretty solid that way. When I rotate the wheels, they move freely but make a light rubbing sound. I also notice a little play where the wheel would move a bit before the drive shaft engaged and moved. Does anyone know if that is normal? I have noticed that on the highway, especially in 5th gear, there is bit of thunk when going from coasting to getting back on the gas, and you can feel it re-engage.

    I appreciate any help with this or any ideas/suggestions before I start throwing money at it.
  2. Sounds like bad wheel bearings but do the simple 1st. How are the brake pads?
  3. I hate to say it but this sounds typical of an improperly setup rear end. What was the original reason to change the bearings? The in and out play you notice is normal to a certain extent and is just the movement of the axles and c-clips to the center pin. Some play here is normal and I would not suspect you to have a problem with one of the c-clips. The engagement that you speak of can be technically described as backlash on the ring gear. This should be measured with a dial indicator with the rear cover off of the housing. The clunking you hear can very well be from excessive backlash due to improperly setting up a rear end. Were the gears changed, new shims installed and setup correctly? I have seen plenty of PRO mechanics get rear end gears wrong in the past. I'm in no means knocking the guy who did the work, but would definitely go over it to be sure. It also is possible that you have a bad wheel bearing and they would be easy enough to change when the rear cover comes off to check things out.
  4. Thanks guys. The brakes were done when I had the pinion and carrier bearings replaced, and now that I really think about it, it was more like 20k miles ago. The bearings were replaced because they were making an aweful howling noise, so they were clearly shot. I had it diagnosed by the local dealer and by the shop that did the work. The gears were not changed when this was done. Not really sure what else was replaced. He did say the gears looked good at the time. I don't really beat on the car or race it, so I would think after 20k miles, most on the highway, at least those bearing would be holding up well. But it sounds like if they didn't put things back together properly, it could cause some additional issues.
  5. I tend to agree with 84Ttop. If the carrier bearings were not preloaded after everything was dialed in then the backlash over time may have opened up to the point of making noise. Doesnt sound like a pinion depth issue to me.