Quote:
Originally Posted by cwebster
The procedure does not call for applying the TTY until the alignment has been checked and re-adjusted. In your BMW example or any of the other anecdotes mentioned in this thread, how do you know how much torque was applied? Was it actually getting "torqued"? What torque value do you think they used? Could it have been snugged down or tightened to whatever the mechanic "felt" was enough? Could it have been cranked down with an impact gun? Even if it were torqued to the specified (1st Pass) value I wouldn't expect the self-locking nut to come loose. That's not the concern I would have.
These are torqued using the TTY procedure at the factory so they've already been "stretched" the point of plasticity. If someone were to apply the correct procedure a second or third time to the same bolts I would be concerned about catastrophic failure from metal fatigue. If they're just "snugging them up" there would, of course, be less chance of that happening but more of a chance that the alignment wouldn't hold.
If you watched the torque value during that additional 75-90 degrees you would see it reach a plateau. Continuing beyond that point does not increase the torque. It only weakens the metal. If you've ever snapped off a bolt you get the idea - except most bolts aren't designed to stretch and give like these, which is why it's easier to snap them off when over-torquing.
Maybe someone will step up and actually test this to see how many TTY applications it takes to make it fail. Or whether you can maintain the adjustment using a single torque value(??). Maybe someone already has?
I don't know any more than any of you why the engineers made the decision to use these bolts, but they did. Maybe someone close to GM could ask them. I doubt such a question would gain enough momentum to rise to the top of the "Ask Al" list, given the opposition from more longstanding members.
Maybe a better question would be... As seldom as it has happened or is likely to happen, what would be the consequences of control arm coming apart? -or- Do you feel lucky? 
--Cal |
I was just going off my personal experience doing alignments (as part of my job) over the last 15 years. It’s pretty easy for your angles to change as you tighten things down. Or as you adjust the other side of the car. I find myself going back on a regular basis. On some cars, the toe will actually change every time as the eccentric is torqued. So you almost need to anticipate this before tightening everything down. If you don’t, it’ll be off once properly torqued. It’s like trying to hit a moving target.
I just aligned my ZL1 this afternoon, and the suspension and eccentric setup are extremely similar to the BMWs I usually deal with. And I didn’t change the bolts, just like I never have on my 335i. Is it the “right” way to do it? No, but I’m not overly worried about reusing them. But I also didn’t zap them with an impact like a moron, lol. Maybe I’ll replace them next time.
My car wasn’t as screwed up as yours, but it had double the recommended front toe (24 minutes or 0.4 degrees). The spec is 0.2 or 12 minutes. My thrust angle was off a bit due to the right rear being toe’d out. Total rear toe was still in the specified range, but far from perfect.