I shredded my posi clutch disc splines

[Justa6MB]

So last year racing on my 7 year old wore out drag radials I was having traction trouble. So I installed the HR rear bar and new clutch discs from a reputable vendor. Raced earlier in the year and just turned it down to keep the tires under it. Yesterday I went to the track with new slicks on it for the first time. Headed to the line with utmost anticipation, 2800 rpm - 4 psi foot brake launch with zero ramp, 23 psi. Felt it break traction a few times and some kind of shake at the top of first. After that I had an open diff. Pulled the cover and spiders out today and found the disc splines are totally shredded. I still had the oem’s I pulled out last year so I slid them on the spiders and they’re tight as can be. Did I get a shitty set of discs? Anybody had similar issilues? Is there anything I could’ve done wrong?


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[Justa6MB]

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[mikestertwo]

Did it shear one side or both? If only one side...which side?

 

[Justa6MB]

Both sides are stripped right out.


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[bison]

The clutch splines likely failed during a burnout. Did you notice the problem during a burnout? The clutches themselves do nothing to hold any axle torque during a pass. The torque to each wheel is equal till one slips.


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[Justa6MB]

Yeah I suspect it happened on the first burnout as there was no rubber on the car at all behind the DS tire. I did put in the heavier spring with the clutches. Don’t really want to have it happen again. Should I put the old spring back in with new clutches?


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[Justa6MB]

Still looking for help with the “Cause”. Don’t want to just put new discs in and have the same thing happen first time out. Do I need to do something different during the burnout to prevent this? Or like I said put in the stock spring?


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[bison]

Still looking for help with the “Cause”. Don’t want to just put new discs in and have the same thing happen first time out. Do I need to do something different during the burnout to prevent this? Or like I said put in the stock spring?


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I can’t see just the spring causing the problem. Maybe run a file over the stock clutch splines and one over failed spline area. A quick hardness test. Maybe it missed the heat treat process? There’s no way to know for sure without testing. I haven’t seen this failure before


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[mikestertwo]

Did the clutch disks fit on the side gears snuggly or were they a loose fit? I have never seen a failure like that. When you installed the clutches did you check to make sure the clearance from the face of the side gears to the pin was equal? That's important so the load on the clutch packs are equal. There's a selective washer under each clutch pack. Can you post a picture of a failed clutch disk?

 

[Jerryl]

I installed the HR rear bar and new clutch discs from a reputable vendor.

Like Bison said: Probably a material issue with the disks.

 

[Justa6MB]

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[Justa6MB]

I ran a file across the teeth of one each and counted the strokes. They appear to take about the same amount to file. When installing I paid close attention to ensure the shims went back in like they came out. And was also careful to check vs instructions when I pulled it apart yesterday. But I didn’t measure the pin to gear side to side. Also I’ve always rolled out of the burnout. Is it possible one tire just stuck as I rolled ahead under power and they just couldn’t take it? SHOULD IT TAKE IT? Moser 28 spline, c-clip elims. Also I can’t say for sure if they were as tight as the originals. I’d usually check that kind of thing. I know they are still nice and tight.


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