1. Trevor B

    Trevor B FABO Gold Member FABO Gold Member

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    Last night at the drag strip, I experienced a sound/feeling that spelled bad news.
    It was my 5th run of the night and somewhere in 2nd gear I felt and heard a big vibration and shaking, can't really call it a grind but it was hard to really hear over the engine and the guy next to me. I felt nothing in 1st and it went away when I shifted to 3rd. My ET was right around where it usually is: 12.52", so it was certainly pulling like normal.

    Below are the specs of the car and then the history of this transmission:
    1973 Dart Sport 340 body (everything else from my '73 Duster)
    380/360 Mopar Magnum crate engine
    3000 stall Hughes Performance TC
    Transmission cooler (not using radiator tank)
    Reverse manual valve body
    3.92 rear gears
    Mickey Thompson slicks

    I typically run the electric fan to keep the transmission as cool as possible right up until I stage. Then I turn it off. That said, it was 54 degrees at the end of the night and the car had been sitting for about an hour.
    I do a good burnout and typically launch at about 2500 rpm and shift between 5500 and 6000.

    History
    The engine and transmission came out of my previous race car ('73 Duster).
    The driveshaft and rear end were rebuilt for this version.
    I had the original transmission rebuilt about 5 years ago by a local guy, no longer in business. He put in a TF-2 kit and did a stock rebuild (no special high end stuff).
    It never really shifted as hard or as accurately as I liked.
    So two years ago I put in a bigger stall converter and the reverse manual valve body and saw big gains on the track with super tight and accurate shifts (no slop between 1st and 2nd like before).
    Last week I changed the transmission pan gasket and put in new fluid. There were no chunks or anything in the fluid, maybe a little cloudy.

    Previous concerns:
    The Duster (previous incarnation) always had a weird, almost harmonic vibration while cruising in 3rd at about 2300 rpm, the pulses would get faster and then fade away upon acceleration and slower/fade away when decelerating. It was most obvious on the highway. I had the driveshaft rebalanced and it didn't change. I didn't know if it was the rear end or the transmission but don't think it was the engine.

    In the current car (Dart), the vibration was much less present but I think it was still kind of there. That ruled out the rear end, as it was a totally different everything from housing to gears to new axles. But I never did much street driving as it was set up for the track, not registered or insured (and looks like it - the car begs to be pulled over!).

    It ran strong all last year, never a hint of a problem, and super consistent.

    This spring, after sitting all winter, when I started it, it was rich misfiring very badly and shaking like crazy. It even shook some wires loose. When I got that taken care of (choke adjustment), I heard a lot of clattering from underneath. I finally located the source of the problem: 3 of the 4 torque converter to flex plate bolts were really loose. I locktited them and torqued them back and the car ran/felt/sounded perfect again.

    Last night was my first night back at the track. First run was totally normal. I had a missed shift on my second run, where I skipped 2nd gear and hit 3rd instead. I immediately shifted back to 2nd, tached up as normal, and went to 3rd. Nothing felt out of the ordinary. This is the first and only time I've ever done this.

    My third and fourth (next two) runs were perfectly normal and the car is extremely consistent.

    Then on the fifth run, I experienced that shaking. The drive back on the return route felt normal, but I was only going about 25 mph.

    So here I am. I realize that I've been beating the snot out of this transmission but wanted to throw this out there to see if any of your gurus had any thoughts or ideas. Thanks in advance!
     
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    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      You checked your lugnuts, and U-joint straps right, and engine tie-down.?
       
    • rustycowll69

      rustycowll69 Well-Known Member

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      and trans mount. My late friend killed two extension housings, by not having enough spline engagement on output shaft(driveshaft too short).
      Another (outside)possibility is bent driveshaft. Try indicating the shaft tube with the ends in v-blocks or rollers.
       
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      • Trevor B

        Trevor B FABO Gold Member FABO Gold Member

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        Thanks, guys. Will get to car later today and go a little deeper. Initial inspection didn't turn up any obvious loose stuff.
        So it doesn't sound like transmission-related?
         
      • CudaFactHackJob

        CudaFactHackJob FABO Gold Member FABO Gold Member

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        You had a vibration; one time; in second gear?
         
        • Thanks! Thanks! x 1
        • Trevor B

          Trevor B FABO Gold Member FABO Gold Member

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          It was a hell of a vibration + shaking and made a fairly loud noise I'd never heard before. In second gear only.
           
        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          Could have been a loss of traction. Go out on the street and do it again and see what happens. If it's a transmission problem, it's already broken. Not like you're gonna hurt it anymore tying to find out what it is.
           
        • Trevor B

          Trevor B FABO Gold Member FABO Gold Member

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          That is a very interesting thought - thanks! The track was definitely much colder at that point in the evening and I'm sure they didn't do a very good job conditioning it this year. In fact, last week was the first night they opened up the entire 1/4 mile (three previous weeks were 1/8 only).

          It may be a little tricky to try to replicate on the street around here but maybe I could trailer it out to somewhere quiet.
           
        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          Look at it this way, If you cannot get it to duplicate, maybe there's nothing wrong.
           
        • Charrlie_S

          Charrlie_S Well-Known Member

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          check the flex plate. you might have hurt it with the loose bolts. might have a crack.
           
        • rustycowll69

          rustycowll69 Well-Known Member

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          what type of balance weight do you have on converter or flexplate? maybe you shucked a balance weight.
           
        • 67Dart273

          67Dart273 FABO Gold Member FABO Gold Member

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          You can deduce a lot if you just "think". Normally a driveline/ engine vibration is so much higher in frequency than an axle/ wheel/ tire/ traction vibration, that you can often separate them immediately

          Such things as bent driveshaft/ bad U joint/ loose pinion yoke or with stick, maybe a torn up clutch disk and so on. All those have a VERY high vibration frequency, more of a buzz than a "thump"

          Have you pulled the driveshaft and checked the U joints? You can NOT check U joints by shaking the shaft in place. You MUST pull the shaft and carefully move them while feeling for dry/ rough movement. The would be the most basic of all failures.
           
        • CudaFactHackJob

          CudaFactHackJob FABO Gold Member FABO Gold Member

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          OMG don't let 3R give you the 357 repair recommendation!!
           
        • Trevor B

          Trevor B FABO Gold Member FABO Gold Member

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          Update:
          I took the car out to put her through her paces on a long and straight road. Problem is worse.
          I warmed up the engine on the trailer.

          Went out in first and stayed in first through about 5000 rpm, then coasted back down again.
          Then repeated in second, stayed in second.
          Then third, staying in third.

          Then came back, going through the gears.

          At the beginning, in first gear, everything felt pretty good, although I think I started to feel that pulsing again as we got up to about 40-45.
          Second gear, the pulsing vibration came back and seemed to get stronger and more constant - that is to say the "pulse" got longer and longer until it was a steady vibration. Low pitch, could feel it in the whole car.
          Third gear, vibration turned to a roar and I could hear other things vibrating - I think even the exhaust was banging against something (it's pretty tight to the body on the left side).

          The faster we went, the worse it got.

          It sounds like it is coming from behind me (somewhere).

          I did not feel the vibration more in the steering wheel than anywhere else.

          It occurs to me that as I went further, everything was probably heating up more and more.

          The engine and transmission worked together as normal and pulled like normal. Nothing felt like it was slipping and definitely no wheel hop.

          I came home and pulled the driveshaft. U-joints are in great condition (and everything was nice and snug before I pulled it). I could see no evidence of balance weights missing - this drive shaft got new u-joints and was balanced right before I started racing it in November. I put a straight edge on it all around and it is straight.

          The flex plate looks okay to me. I don't see anything missing or anything to suggest that it has come apart.

          At this point I'm wondering if it might be in the rear end itself. The 8.25" sure grip rear end got new axles and a new 3.92 gear set last summer, done by a professional I have no reason to distrust. It has always had a little bit of a whine, though.

          One thought, although it is a bit of a pain in the neck: I have the old 8.25" sure grip with 3.55 gears on my Barracuda and it is in good shape. I suppose I could swap out the rear ends and that would answer any questions about the rear end. Actually, for that matter, I have the Barracuda's original 7.25" sure grip small bolt pattern 3.23 rear end in my garage and possibly the driveshaft that went with it.
           
        • dartfreak75

          dartfreak75 Restore it, Dont part it! FABO Gold Member

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          ????
           
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