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Technical Setting up O.E.M. (FoMoCo) 9" to remove whine?

Discussion in 'Traditional Hot Rods' started by crusin55, Nov 26, 2015.

  1. crusin55
    Joined: Jun 12, 2006
    Posts: 205


    I have an O.E.M. 9" 3rd-Member out of a 70's Mustang. It has original gears (FoMoCo). It has a slight whine between 40-60 mph. It comes in at 40 mph and goes away at 60 mph. It also has a clunk when you snap off the gas and clunks again when you get into it fast or rather hard. Normal driving you don't hear the clunk.

    My question.....Is it possible to take this O.E.M. and have it gone over (bearings, lash and etc.) and get rid of the whine and clunk? If I could get rid of the clunk..........I could live with the whine.

    Your thoughts..........Please!!!!
  2. pack it full of cheese.........
    It just needs to be reset with new bearings, possibly a worn pinion bearing.
    Joined: Nov 10, 2005
    Posts: 846

    from Holly

    It depends on how much the r/pinion is worn and where the pattern is on the teeth. If it was set up correctly to begin with. Very hard to dial out the whine if gears are permanently scarred.
  4. Stock Racer
    Joined: Feb 28, 2010
    Posts: 640

    Stock Racer

    Absolutely. Gonna have to tear it down. Check backlash, gear pattern, bearings etc. Upon inspection your problem usually shows up. I was always told if everything else is correct, a whine is usually caused by a bad pattern on the coast side.
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  5. panheadguy
    Joined: Jan 8, 2005
    Posts: 995

    from S.E. WI

    The clunking sounds like too much r&p lash. Probably all is worn and needs a rebuild.
  6. crusin55
    Joined: Jun 12, 2006
    Posts: 205


    This is a video of the noise.

    1. Click on the Attachment
    2. At the bottom of the on Open
    3. Let it load 100%
    4. Double click on IMG_0699
    5. Turn up your volume

    Attached Files:

    Last edited: Nov 30, 2015
  7. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,834


    Yeah, then he'll have whine & cheese.
    Hnstray likes this.
  8. How bout your u-joints for the clunk? They're inexpensive and not too hard to replace.
  9. Easy question to answer, your rear is loose from wear, rebuild it and set it up to spec. you may already have a bad wear pattern on the gears and need to replace them.
  10. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,566

    from Quincy, IL

    Driveline "clunk" can also be found in a worn yoke and output shaft splines at the transmission/driveshaft junction. Not saying you don't have a 3rd member issue, only that it may not be limited to the 3rd member.

  11. I had a master bearing kit put in my 9 inch with new gears. Still has a slight whine after 3 seperate adjusts by a very experianced builder. Had a clunk to but he said it was the drum in the trans. He was thinking the 3rd member housing is off a bit.
  12. crusin55
    Joined: Jun 12, 2006
    Posts: 205


    Sent it back and they said everything checks out OK. They did say the bearings showed excessive scoring with only 500 miles. They said it could be caused by Low Oil Level, Wrong Oil or Contaminated Housing. NOT....I bought oil they suggested, filled it to the bottom of the plug hole and wiped the housing clean with Brake Kleen before installation.

    I think it was defective bearings installed or improperly installed. They offered to build me a new one or give me a full refund. I opted for a full refund. They put it through the same day.

    It took 4 months from time of order to refund. Glad it's over!!!! I put my old 9" back in that only had a slight whine between 40-60mph. I can live with that after that terrible noisy new rebuild.

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