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JZA70 448 rwhp everyday
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Discussion Starter · #1 ·
well i had a strange low rpm clunking sound coming from my tranny. I got under there today and found that the grade 8 bolts that hold the pressure plate to the flywheel were all severed, with damaged threads! I was planning on pulling the motor for my single install any ways so im not mad about having to pull it but what would cause this? I torqued the bolts to spec, and i labeled the bolts that came from the 7m set up. I used the same clutch / pressure plate only change was the 1j flywheel which i had re surfaced??? On another note i cant believe the car still drives fine, hopefully i didnt damage anything else.

~scott
 

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well, there are a number of questions that may help you answer the problem:

are these toyota bolts or aftermarket (eg home depot)
did you use any threadlocking agent?
how did you torque the bolts?
what does the fracture surface of the bolts look like?

if you used aftermarket bolts, there is a chance that they were miscut/misthreaded which could have resulted in either fatigue fracture or tensile fracture. As you said you labelled the bolts, i assume they weren't new. Perhaps there were shavings caught in the flywheel holes from machining which damaged the threads as you were torquing the bolts.....

there are alot of possible causes for the bolts to fracture....get a high-res closeup pic of a few fracture surfaces and i could be of better help.

adam
 

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JZA70 448 rwhp everyday
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2,994 Posts
Discussion Starter · #3 ·
ill get the pics of the bolt i removed. The bolts are toyota, lock washers were intact, red loctite was used, bolts were tightened in cross sequence then the final torque setting was applied also in cross sequence. The threads could have been dirty i dont recall cleaning them.

~scott
 

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If you didn't have the dowel pins put back in the fly wheel the bolts would take the full shear force. but it still should have held up. They could have came loose slowly then the dowels no longer held and they snapped. But for that scenareo to happen is kinda unlikely as there would have been no grip on your friction disc to drive the car. So perhapse they came slightly loose and there were no pins causing them to shear.
 

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JZA70 448 rwhp everyday
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2,994 Posts
Discussion Starter · #5 ·
funny thing is the car still is driveable, im obviously not driving it any more but dang.

~scott
 

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JZA70 448 rwhp everyday
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2,994 Posts
Discussion Starter · #8 ·
yea i was just guessing at grade 8, didnt know that metric didnt come like that. Yes they were stock!

~scott
 

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Metric bolts come in grade 8.8 (the lowest common bolt), grade 10.9 (SAE spec grade 8, non shear) and grade 12.9 (the toughest damn bolts you'll ever see)

Eric
 

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JZA70 448 rwhp everyday
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2,994 Posts
Discussion Starter · #10 ·
when i get her back together im gonna be sure to get new bolts from toyota, no use in risking using hte wrong thing. I still cant believe that it runs and the clutch doesnt even slip!

~scott
 
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