Quote:
Originally Posted by clg82
Interesting so only the rears are TTY...I thought the front was as well, learn something new every day.
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Quote:
Originally Posted by RamAir02
I'm not sure if this is true 100% of the time, but an easy tell for a TTY bolt is if the torque spec is [XX] lbs. ft. + [XX] degrees OR [XX] fractional turn. Non-TTY bolts usually just have a numerical torque spec.
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This is not entirely true. There are torque to yield (TTY) and there are torque to angle (TTA). Any tightening that includes an angle does not mean it is automatically a bolt that is one time use TTY. If we look at many suspension and brake fasteners on the Gen6, GM calls out certain bolts as one time use TTY while there are others that are not one time use yet they have a torque + angle tightening (TTA) spec.
Quote:
Originally Posted by Mark R
On a stock car, there are 4 bolts up front that need replacing. Those are the bolts at the bottom of the strut. In back, you need two control arm bolts that adjust the camber, and the two toe rod bolts for...toe.
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This is incorrect. The 4 large strut to knuckle bolts are not TTY. They are TTA. They are not called out in the service manual as one time use.
Quote:
Originally Posted by RobZL1
According to the linked post earlier in this thread, it's only the bolts in the rear that need replacing. The front strut-to-knuckle bolts are not designed to yield.
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When we tighten ANY bolt to its engineered final spec we are stretching it on purpose. This stretch plays a part in it staying tight, or IOW, this stretch creates a predetermined load. There are many factors that play a part in the ultimate load a fastener creates. When a fastener is yielded, this means that the bolt was permanently stretched (deformed) beyond the point where it will not return to its original length. Any bolt can be yielded. The TTY bolts are engineered to slightly go past the yield point to get maximum clamping force. Sometimes the TTY bolt will have a narrower shank or the metallurgy will enable it to yield at a more specific point. If a yielded bolt is reused, more often than not it cannot create the same clamping force that was engineered when it was tightened the first time. One way to tell is if you keep turning the nut or bolt head and it gets to a point where its tightness levels off. You can keep tightening it and it never really tightens up. If you get to this point and remove the fastener, you may find that the stretch is very noticeable. A grade 5 or (or metric 8.8) bolt will stretch more before it breaks compared to a Grade 8 (or metric 10.9).
The front strut to knuckle bolts can reach a point of yield if they are overtightened. That is why any important fastener should be tightened to its spec.