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  •  » Chasing that 80+mph vibration

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    3/22/2023 6:31 PM  #101

    Quicksilver
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    From: California Central Coast
    Registered: 9/22/2013
    Posts: 309

    Re: Chasing that 80+mph vibration

    Did you ever end up taking her in for a dyno check up and find out what kind of HP she is putting out??

    Money can't buy happiness. Butt it can buy Car Parts... and that is pretty much the same thing.67 FastBack
     

    3/22/2023 6:39 PM  #102

    Bentworker
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    Registered: 9/17/2017
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    Re: Chasing that 80+mph vibration

    Lol @ RTM

    I do the same thing.

     

    3/22/2023 7:58 PM  #103

    HudginJ3
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    From: Cedar Hill, TX
    Registered: 4/29/2015
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    Re: Chasing that 80+mph vibration

    I do to so I can compare notes. I had my car jacked up and the tires and brake drums of of it. I ran it up to 80 and more and while it was vibrating I crawled under it to "see" the vibration. There was nothing to see or feel in the driveshaft or differential. I didn't do it again because I was skiret to crawl under the car with it running like that. Im thinking it has to be in the trans.

    70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
     

    3/23/2023 4:03 AM  #104

    50vert
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    From: QLD Australia
    Registered: 4/01/2013
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    Re: Chasing that 80+mph vibration

    How did the gopro idea work out .... inconclusive?

    "Those telephone poles were like a picket fence"
     

    4/16/2024 8:31 PM  #105

    HudginJ3
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    From: Cedar Hill, TX
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    Re: Chasing that 80+mph vibration

    FOUND IT!!!   Wasn’t me.  I took the Mustang in to redo the exhaust system and he had to remove the drive shaft. The rear U joint had one cap that was nothing but powder. Glad thats over.

    70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
     

    4/17/2024 5:09 AM  #106

    BTaylor
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    From: Carrabelle, FL
    Registered: 4/02/2013
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    Re: Chasing that 80+mph vibration

    Do you still have the factory transmission dampener attached?
     

    1973 Corvette
     

    4/17/2024 8:01 AM  #107

    HudginJ3
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    From: Cedar Hill, TX
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    Re: Chasing that 80+mph vibration

    No, I removed the original 3 speed and installed a 94 T5 using a modified trans mount and an 85 T- bird driveshaft. I took the drive shaft in to have it balanced a they discarded the dampener that was on it and installed new u joints.

    70, ragtop 351W/416 stroker Edel Performer heads w pro flow 4, Comp roller 35-421-8. T5
     

    12/19/2025 7:48 PM  #108

    BroPaul
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    From: Fresno CA
    Registered: 10/04/2023
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    Re: Chasing that 80+mph vibration

    MS wrote:

    RTM wrote:

    Every time I see a new post on this subject I rush to see if the problem was found. Lol

    Hopefully someday

    From another forum - 

    I do have a funny story to share from about a month ago. I had dropped the car off at a shop to chase down an intermittent vibration at highway speed I had been unable to find. The guy that owns the shop is a successful dirt track racer and hotrodder. I figured the guy makes his living making sure his race cars are dialed in right, he's probably the guy to find the problem since I had tried everything I knew to do.

    It appears he discovered the problem however. Turns out the spring pads on the rear axle were 1.5 degrees rotated from each other and putting the springs into a bind. Crazy thing is, near as we can figure is those are factory welds on the pads, so I guess the axle got a twist in it at some point. He chucked the lowering blocks into the mill and angle cut them. Problem solved.

    65 Fastback, 422W, Roller C4, 14" front discs, 9" rear,  front coilovers, SorT A-arms
     

    12/20/2025 6:50 AM  #109

    BobE
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    From: White Plains, NY
    Registered: 4/04/2013
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    Re: Chasing that 80+mph vibration

    RCodePaul - good feedback, thank you.  Never had given this a thought, now it is something to consider. 

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    12/20/2025 9:45 AM  #110

    Nos681
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    From: Atlantic Mine, Michigan
    Registered: 7/14/2016
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    Re: Chasing that 80+mph vibration

    Spring perch differences had not crossed my mind.
    Thanks Paul.

     

    12/20/2025 10:56 AM  #111

    rpm
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    From: Bakersfield, Ca
    Registered: 9/17/2013
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    Re: Chasing that 80+mph vibration

    Wow. I can't imagine anyone else thinking of measuring both spring perches.

    Last edited by rpm (12/22/2025 12:09 PM)

    Bob. 21.5 freeway MPG 69 Mach 1, 5.0 GT40P heads, SMOD Toploader, Armstrong  steering, factory AC
     

    12/22/2025 7:31 AM  #112

    RTM
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    From: Cape Coral FL
    Registered: 5/22/2019
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    Re: Chasing that 80+mph vibration

    I would have never thought the spring pads would have been a cause for vibration.

     

    12/22/2025 3:34 PM  #113

    BroPaul
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    From: Fresno CA
    Registered: 10/04/2023
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    Re: Chasing that 80+mph vibration

    BobE wrote:

    RCodePaul - good feedback, thank you.  Never had given this a thought, now it is something to consider. 

    Nos681 wrote:

    Spring perch differences had not crossed my mind.
    Thanks Paul.

    Most welcome. Just appreciate it when board members have nice things to say. 

    rpm wrote:

    Wow. I can't imagine anyone else thinking of measuring both spring perches.

    RTM wrote:

    I would have never thought the spring pads would have been a cause for vibration.

    My thoughts exactly. How would you even think of that??? I guess the poster wen to the exactly right guy. "Mr. Wizard!!!" 
     

    65 Fastback, 422W, Roller C4, 14" front discs, 9" rear,  front coilovers, SorT A-arms
     

    12/22/2025 10:43 PM  #114

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
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    Re: Chasing that 80+mph vibration

    rpm wrote:

    Wow. I can't imagine anyone else thinking of measuring both spring perches.

    I did.  On all three rear ends I have had in the car.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
       •Thread Starter
     

    12/23/2025 8:00 AM  #115

    BobE
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    From: White Plains, NY
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    Re: Chasing that 80+mph vibration

    MS wrote:

    rpm wrote:

    Wow. I can't imagine anyone else thinking of measuring both spring perches.

    I did. On all three rear ends I have had in the car.

    Did you find them "off" and needing to be addressed? 
     

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

    12/24/2025 2:00 PM  #116

    MS
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    From: Canyon Lake, Texas
    Registered: 1/24/2013
    Posts: 12,757

    Re: Chasing that 80+mph vibration

    BobE wrote:

    MS wrote:

    rpm wrote:

    Wow. I can't imagine anyone else thinking of measuring both spring perches.

    I did. On all three rear ends I have had in the car.

    Did you find them "off" and needing to be addressed? 
     

     
    No
    But I have tried every pinion angle through a wide range.  Now that I have a new R&P that sits a bit lower, I can start over and angle the engine downward a bit, then match that angle with the rear axle.  Just too many things going on to fond the appropriate round-tuit.

    Money you enjoy wasting is NOT wasted money... unless your wife finds out.
       •Thread Starter
     

    12/26/2025 7:24 AM  #117

    BobE
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    From: White Plains, NY
    Registered: 4/04/2013
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    Re: Chasing that 80+mph vibration

    MS wrote:

    BobE wrote:

    MS wrote:


    I did. On all three rear ends I have had in the car.

    Did you find them "off" and needing to be addressed? 
     

     
    No
    But I have tried every pinion angle through a wide range. Now that I have a new R&P that sits a bit lower, I can start over and angle the engine downward a bit, then match that angle with the rear axle. Just too many things going on to fond the appropriate round-tuit.

    OK, thank you.  Please keep us updated as things move along. 
     

    65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
     

     

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