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Heavy Diff/Axle Clunking Under Hard Braking

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  • Heavy Diff/Axle Clunking Under Hard Braking

    It feels like the rear end wants to pull free of the car, and only happens under braking with the drivetrain loaded. Clutch in, no problems. Engine braking decel, no problems. It was so bad that the right rear stub axle popped out of the housing the last time I took the car out. It's such a violent clunking that I fear I'll break a rear suspension piece and write the car off, so I refuse to drive it hard (which means my Carbotechs squeal like CRAZY) and am probably going to cancel my track days this weekend.

    I'm ordering a new center bearing for the driveshaft. I'm also going to unbolt the driveshaft and rotate it 180 degrees, see if that helps, then try 90 degrees in either direction if it doesn't. No, I did not mark it when I took the diff out, so now I have to guess. I've double-checked all bolts, they're all present and torqued. The 1.5-way diff was professionally installed in the pumpkin by the highest-rated rear end shop in SD county. The wheel bearings feel good.

    It's not an upright bushing issue. I thought it was and it is not; I've replaced all bushings with spherical bearings and the clunking is just as severe.

    The axles have damn near a quarter million miles on them, and I've never done any maintenance on them. Could they be toast?

    Have any of you ever experienced something like this?
    S13
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  • #2
    Subframe or diff bushings still rubber?
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    • #3
      Forgot to add that- no rubber bushings anywhere anymore.

      I'll probably jack it up at lunch and check the subframe mounting nuts as well as any other play.
      S13
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      • #4
        Nothing's loose, but the center bearing has a lot of play. Guess that's my job for tonight.
        S13
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        • #5
          center bearing doesn't seem to fit the bill to me...

          If I was you I think I'd pull the boots of the half shafts and see if theres not something amiss in there, If nothing else you can scoop out and repack the grease so you can atleast say you did it.

          something has to move to clunk...and the axle stub takes quite a bit of movement to come out of the housing, if everything else is bolted tight and there is no rubber there should be no movement

          I think the only thing left that moves is the CV joints ( or whatever type they are)
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          • #6
            Center bearing didn't fit the bill for me, either, but I always get thinking when under a car with a job to do and end up coming up with new ideas.

            First: halibut-flavored ice cream. It'll be a hit in coastal areas when served with a nice olive oil dipping sauce.

            Second: What if it isn't specifically driveline-created? So I got to thinking while under the car and adjusting rebound... what if my dampers are loose in the housings? Pulled 'em apart and they were both at least a half-turn loose. Checked both top mounts and tightened one. Initial testing shows the problem to be gone.

            Also, my rear springs are too short and may come free under full droop. Ordered some assist springs to smooth out the ride and make up for the lack of length. Just kinda jumped into that.
            S13
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            • #7
              Just figured I would throw this out there. I get a large clunk from the diff during heavy braking and turn in, sort of like you describe. Not all the time, just the highest G turns. I was lifting a rear tire. I don't know if this is supposed to make a loud engagement/disengagement clunk or not. I have a cusco 1.5 diff which I've heard are supposed to be really loud. Hopefully what you did fixed your problem, and if not maybe this will be another idea to add to the brainstorm.

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              • #8
                Yeah, it's the lifting of a rear tire; rear OAL is too short for tracks like the Streets or Horsethief Mile where the corners are tight and uphill/downhill with and without camber. I don't know if it's the diff clunking, and it's typically quiet, but it certainly might be.

                I was hoping to mitigate that but even with 9/7 spring rates I still have enough body roll to lift that inside wheel; perhaps I should've increased front sway stiffness to try to limit roll and keep some weight inside.

                I'm still a noob at this whole setup thing and despite being the fastest S-chassis at every track event I go to, I still have a lot to learn.

                Edit: I'm also usually the only S-chassis at my track events...
                Last edited by SOneThreeCoupe; 02-20-2012, 04:01 PM.
                S13
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                • #9
                  Any tender springs on your rears? might help get a little more droop.

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                  • #10
                    also check the play in your rear axles. I had one axle with quite a bit of play in it.. I swapped it out with a parts store unit and the rear end got quieter. with 250k miles on yours, it's quite likely that all of the joints are pretty sloppy.
                    Originally posted by SoSideways
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                    • #11
                      Originally posted by WorkInProgressK View Post
                      Any tender springs on your rears? might help get a little more droop.
                      The only way to get more travel is to change my housings and dampers to longer items.

                      I would love to have another 2" of travel since I still drive the car on the street in the SoCal mountains.

                      Matt, I've decided to do just that this year. My down time between events isn't going to be spent buying new stuff and trying to adapt, it's going to be spent driving the car in the mountains and replacing things like the driveshaft, axles, resealing the trans, replacing the clutch slave, replacing the dripping rack with a HICAS unit, etc.

                      At the track this weekend, the noise and clunking was less evident so what little I did certainly helped.
                      S13
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