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  • humming sound

    Ive noticed on my 84, anytime I have ANY acceleration I can hear a very slight "hum" from the rear. Im guessing its my differential. Its not a roaring sound like a bearing its just a hum. If I let off the gas and let it coast it goes away but as soon as I accelerate the slightest bit it comes back. The car has 80k original miles on it. Im not too much worried about it but wanted opinions.... thanks...
    84' SVO

  • #2
    without hearing how loud it is, hard to say for sure, if there is anything wrong. Will say these year fox'es do have a bit of whine / roar on acceleration. all of them I've been in do anyway. except maybe one, it had a v6/auto, but I just don't think it had enough torque to cause whine.
    Eric C
    SVOCA Webmaster

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    • #3
      Eric.. thanks for the reply. Im not much worried about it. As I said, its like a very low pitched hum, just a little annoying.
      84' SVO

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      • #4
        Originally posted by pfmeeks1966 View Post
        Ive noticed on my 84, anytime I have ANY acceleration I can hear a very slight "hum" from the rear. Im guessing its my differential. Its not a roaring sound like a bearing its just a hum. If I let off the gas and let it coast it goes away but as soon as I accelerate the slightest bit it comes back. The car has 80k original miles on it. Im not too much worried about it but wanted opinions.... thanks...
        Rear wheel bearing? Pinion bearing? U-joint? I think I would:
        1. Get the back end off the ground, pull the wheels and inspect for axle seal and pinion leaks.
        2. Spin the axles and see if you hear/feel anything.
        3. Pull the driveshaft and inspect the u-joints.

        Work outward from there.
        Gene Beaird,
        86 2R SVO, G Stock,
        Pearland, Texas

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        • #5
          Very low pitched hum under acceleration...I would attribute that to just 'normal' driveline vibration coming up through the rear trailing arms. One other possible item could be contact between an exhaust tube and something, as the engine rolls over a bit, the exhaust would rock a bit and hold. Like you mentioned, it isn't an alarming sound and likely nothing critical.
          Ted
          86 SVO Mustang
          17 Cooper S Clubman ALL4

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          • #6
            Maybe it is the fuel pump? Under vacuum, the pump voltage is reduced by a sensor behind the DS strut tower. Under boost, the pump is given full voltage to feed the beast.

            Maybe you can remove the spare tire and see if that is the noise you are hearing.
            Mike S

            '86 SVO 9L Leather
            '86 SVO 9L Road Warrior
            '96 300ZXTT

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            • #7
              It has a single in tank Walbro fuel pump, and an aluminum drive shaft. The pump has always been a little louder than normal when priming. That may be where the noise is coming from.
              Perry Mitchell
              SVOCA#187

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              • #8
                aluminum drive shafts are known to 'sing' under acceleration
                Eric C
                SVOCA Webmaster

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                • #9
                  I turned up the radio along time ago. Solved alot of things! Helps I can't hear anymore also. Have you tried rocking the car while driving to check for wheel bearing noise changing?
                  Bruce

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                  • #10
                    Perry.. I didn't know you had already put a walbro pump in it. I guess you already deleted the pump on the frame ?

                    - - - Updated - - -

                    Originally posted by Bruce View Post
                    I turned up the radio along time ago. Solved alot of things! Helps I can't hear anymore also. Have you tried rocking the car while driving to check for wheel bearing noise changing?
                    That's what ive been doing is turning up the radio LOL. When I had it aligned the tech said he had to tighten one of the rear wheel bearings when he did the alignment, but it was doing this before the alignment. I haven't tried rocking it back and forth to check for a wheel bearing yet.
                    84' SVO

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                    • #11
                      I know you can shim those wheel-bearings (Through the rear-end), how exactly would you tighten them ?
                      Eric C
                      SVOCA Webmaster

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                      • #12
                        I put the Walbro in and removed the frame mounted pump a LONG time ago. If I recall correctly, when it was removed, I used a Ford Ranger fuel filter to make everything fit.
                        Perry Mitchell
                        SVOCA#187

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                        • #13
                          Rear wheel bearings on our rear ends are pressed into the housing, so nothing to tighten...wonder if the flange mounting plate on the end of the axle tube was what was loose??

                          The side-to-side play is determined by the gap between the end of the axle and the retaining pin in the differential. The wear points that could make 'slop' in the axles is the c-clip, diff housing the c-clip rides up against, c-clip notch in the axle and the center retaining pin (i.e.- many points), but even my axles after many track days weren't 'bad' so to speak but they did show wear, which was mainly concentrated on the axle tip where it rode up against the retaining pin.
                          Ted
                          86 SVO Mustang
                          17 Cooper S Clubman ALL4

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                          • #14
                            Here are the screws I was referring to that the tech may have mistaken for a wheel bearing bolt:

                            Axles - Caliper Mounting Bracket Plate.jpg

                            As for the axle side play, here is a good pic that shows the mushrooming I was getting on the ends of my stock axles:

                            Axles - Comparison_C-clip Button.jpg

                            The axle above it is one of my new Dutchman 31-spline axles before installation for reference. Looks like I didn't snap a pic of the center retaining pin with its wear from the axles, but there was a slight flat worn into the pin, but nothing compared to the tip of the axle. Here is the 'lovely' colorful tips of those axles as well, showing that they were getting heated up pretty good at some points in their lives. Guessing my track days can be to blame for that

                            Axles - C-clip Land_OEM_01.jpg Axles - C-clip Land_OEM_02.jpg
                            Ted
                            86 SVO Mustang
                            17 Cooper S Clubman ALL4

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