How do I stop my rear end from bouncing?

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    Author Topic: How do I stop my rear end from bouncing?  (Read 3504 times)

    Offline Doomed

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    How do I stop my rear end from bouncing?
    « on: November 06, 2011 - 11:21:34 AM »
    So heres the deal - while driving, my rear end is bouncing like crazy. My pinion snubber is fully retracted and is hitting my floor and now i'm having vibrations. Initially the vibrations were only at 70 mph, now it starts at 50mph. There is not a lot of backlash, and the front seal is starting to leak.

    I have an 8 3/4 fully rebuilt, Hotchkis sway bar, QA1 adjustable shocks, XHD mopar leafs, Dr. Diff 1 1/2" relo kit, xv chassis stiffening kit...

    Any help would be appreciated.

    Kyle.
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    Offline brads70

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    Re: How do I stop my rear end from bouncing?
    « Reply #1 on: November 06, 2011 - 12:10:35 PM »
    What's your pinion angle?

    What do you have for rear suspension? stock leafs?
    « Last Edit: November 06, 2011 - 12:39:05 PM by brads70 »
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    Brad
    1970 Challenger 451stroker/4L60 auto OD
    Barrie,Ontario,Canada
    Proud to own one of the best cars ever made!!!!!

    My restoration thread 
    http://www.cuda-challenger.com/cc/index.php?topic=59072.0
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    Offline burnt orange

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    Re: How do I stop my rear end from bouncing?
    « Reply #2 on: November 06, 2011 - 12:23:59 PM »
    How do I stop my rear end from bouncing?   :roflsmiley:

    At first glance I thought this topic should have been in the "Jokes" section.
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    Offline footin70rt

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    Re: How do I stop my rear end from bouncing?
    « Reply #3 on: November 06, 2011 - 12:41:08 PM »
    Just a thought here but how old are the tires? If you have a belt starting to separate it can cause quite a vibration that can also come and go with different road speeds.    :2cents:
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    Thomas
    Driving the same 70 R/T since October 1985
    Native of Bozeman, MT

    Offline Doomed

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    Re: How do I stop my rear end from bouncing?
    « Reply #4 on: November 06, 2011 - 12:54:19 PM »
    Quote from: brads70 on November 06, 2011 - 12:10:35 PM
    What's your pinion angle?

    What do you have for rear suspension? stock leafs?

    Brad - I believe the angle is 5*, but i will have to double check. As for suspension- Hotchkis sway bar, QA1 adjustable shocks, XHD MP leafs, Dr. Diff relo kit, XV chassis stiffening kit...

    Footin - brand new Nitto 555's

    Kyle.
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    Offline brads70

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    Re: How do I stop my rear end from bouncing?
    « Reply #5 on: November 06, 2011 - 03:11:12 PM »
    Quote from: Doomed on November 06, 2011 - 12:54:19 PM
    Brad - I believe the angle is 5*, but i will have to double check. As for suspension- Hotchkis sway bar, QA1 adjustable shocks, XHD MP leafs, Dr. Diff relo kit, XV chassis stiffening kit...

    Footin - brand new Nitto 555's

    Kyle.
    I always shoot for 3 degs angled down?  If it's leaking I'm wondering if the pinion bearing is on it's way out? Any movement there? up-down, in-out?
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    Brad
    1970 Challenger 451stroker/4L60 auto OD
    Barrie,Ontario,Canada
    Proud to own one of the best cars ever made!!!!!

    My restoration thread 
    http://www.cuda-challenger.com/cc/index.php?topic=59072.0
     My handling upgrade post
    http://www.cuda-challenger.com/cc/index.php?topic=73985.0

    Offline HP2

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    Re: How do I stop my rear end from bouncing?
    « Reply #6 on: November 07, 2011 - 09:37:18 AM »
    Quote from: Doomed on November 06, 2011 - 11:21:34 AM
    QA1 adjustable shocks

    Where are these set at? You should be 3-5 clicks up from zero. Zero them out, then click back up and test drive.

    Typically a rear end won't just bounce while just driving down the road, unless there is some sort of binding, interference, or out of round condition on something. If the shocks are worn, or not adjusted up enough, the springs will continue to oscilate after going over irregularities, so we have two different situations for bouncing. Which one more closely ressembles yours?

    Vibrations that change in rpm, intensity, or frequency usually point to an item, such as bearings or joints, wearing out.
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    Offline dodj

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    Re: How do I stop my rear end from bouncing?
    « Reply #7 on: November 07, 2011 - 03:49:46 PM »
    Quote from: Doomed on November 06, 2011 - 11:21:34 AM
    There is not a lot of backlash, and the front seal is starting to leak.

    I have an 8 3/4 fully rebuilt,

    Kyle.
    The rear being fully rebuilt, vibration, and the pinion seal leaking would make me check the rear u-joint and the pinion nut for starters. Maybe end up pulling the pumpkin out.  :(
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    Scott
    1973 Challenger  440 4 spd 
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    Offline brads70

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    Re: How do I stop my rear end from bouncing?
    « Reply #8 on: November 07, 2011 - 05:44:12 PM »
     :iagree:   I'd pull the pumpkin and double check stuff, wear pattern, bearings, backlash. If it's all new and the seal is leaking sounds like trouble to me?
    With the pinion snubber.... is it hitting the floor all the time? Like making the suspension solid? That in it's self would cause some bouncing.
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    Brad
    1970 Challenger 451stroker/4L60 auto OD
    Barrie,Ontario,Canada
    Proud to own one of the best cars ever made!!!!!

    My restoration thread 
    http://www.cuda-challenger.com/cc/index.php?topic=59072.0
     My handling upgrade post
    http://www.cuda-challenger.com/cc/index.php?topic=73985.0

    Offline brads70

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    Re: How do I stop my rear end from bouncing?
    « Reply #9 on: November 09, 2011 - 05:26:17 PM »
    I had a thought about your " bouncing" today..... You say your bottoming out the pinion snubber? I wonder if your also bottoming out the shocks? :clueless:
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    Brad
    1970 Challenger 451stroker/4L60 auto OD
    Barrie,Ontario,Canada
    Proud to own one of the best cars ever made!!!!!

    My restoration thread 
    http://www.cuda-challenger.com/cc/index.php?topic=59072.0
     My handling upgrade post
    http://www.cuda-challenger.com/cc/index.php?topic=73985.0

    Offline Doomed

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    Re: How do I stop my rear end from bouncing?
    « Reply #10 on: November 12, 2011 - 08:56:12 AM »
    Quote from: HP2 on November 07, 2011 - 09:37:18 AM
    Where are these set at? You should be 3-5 clicks up from zero. Zero them out, then click back up and test drive.

    Typically a rear end won't just bounce while just driving down the road, unless there is some sort of binding, interference, or out of round condition on something. If the shocks are worn, or not adjusted up enough, the springs will continue to oscilate after going over irregularities, so we have two different situations for bouncing. Which one more closely ressembles yours?

    Vibrations that change in rpm, intensity, or frequency usually point to an item, such as bearings or joints, wearing out.

    HP2 - I did start out at zero and have adjusted everytime I go out, with little results. I just do not get enough road time to get enough info. To clarify, should I be turning to the + or -?
    As for binding, I see no indication of this, the shocks are new and not worn but the spring are oscilating so I must be improperly adjusting the shocks.

    Kyle.
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    Offline Doomed

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    Re: How do I stop my rear end from bouncing?
    « Reply #11 on: November 12, 2011 - 09:02:25 AM »
    Quote from: dodj on November 07, 2011 - 03:49:46 PM
    The rear being fully rebuilt, vibration, and the pinion seal leaking would make me check the rear u-joint and the pinion nut for starters. Maybe end up pulling the pumpkin out.  :(

    Dodj - Nut is tight, U joint is good.

    Kyle.
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    Offline Doomed

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    Re: How do I stop my rear end from bouncing?
    « Reply #12 on: November 12, 2011 - 09:12:47 AM »
    Quote from: brads70 on November 07, 2011 - 05:44:12 PM
    :iagree:   I'd pull the pumpkin and double check stuff, wear pattern, bearings, backlash. If it's all new and the seal is leaking sounds like trouble to me?
    With the pinion snubber.... is it hitting the floor all the time? Like making the suspension solid? That in it's self would cause some bouncing.

    Brad - the snubber is not hitting all the time, but when on the hoist you can see the wear pattern. I do hear /feel a clunk often when shifting for 2nd to 3rd, thats when the snubber is connecting.

    Kyle.
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    Offline dodj

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    Re: How do I stop my rear end from bouncing?
    « Reply #13 on: November 13, 2011 - 07:38:15 PM »
    Well if the snubber is hitting after a shift your springs must be allowing the axle to rotate quite a bit. How far is the snubber off the tunnel plate at rest? Did you go over all the rear suspension bolts to make sure all is tight? Shackles, hangers, u-bolts, lug nuts, etc..
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    Scott
    1973 Challenger  440 4 spd 
    2007.5 3500 6.7 Cummins Diesel, Anarchy tuned.
    Good friends don't let friends do stupid things. ........alone.

    Offline Doomed

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    Re: How do I stop my rear end from bouncing?
    « Reply #14 on: November 20, 2011 - 09:01:40 AM »
       Alright, I pulled the driveshaft yesterday to replace the leaking seal, and I was able to turn the pinion nut off with my fingers! Looks like it backed off causing the vibrations. On the highway at 130-140 kmh there may be a slight vibration, but I think that may my paranoia kicking in.
       
        I also adjusted my rear shocks to the full negative setting, and the fronts full negative plus 2 clicks - this took the car from being a jaw rattling bouncing mess, to a smooth sailing ride. I still need to further dial it in, but I finally have a reasonable starting point.

    Going to do some more testing today - November 20th in Southern Ontario Canaduh!!!

    Thanks for the help,
    Kyle.
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