Stock Ubolt Replacement

evilunclegrimace said:

Yes the table looks like a misprint for the 1/2" bolt

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Schurkey said:

If "9" is really intended to be "90", and the note at the end of that table says they generally try to achieve 90% of the listed "maximum" torques...GMs spec of 81 is 90% of 90 ft/lbs.

But are the GM bolts 1/2" on the lighter-duty trucks? I kinda think so.

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evilunclegrimace said:

I under stand that different bolts have different torque specs . You stated that you "torqued your bolt to the 100's on a guess and they came loose" that is a perfect example of why you use an actual torque wrench and then retorque certain fasteners after a specified time/mileage.

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Supercharged111 said:

That's the first time I've ever had a u bolt back out. The gun I used would have sufficed for the 1500, but it wasn't enough to to get that 9/16" bolt tight. I could feel how much was left to get the 9/16" down when I tightened it by hand with the breaker bar. I didn't have the luxury of a torque spec at the time, but I'm telling you 120# was not enough for those bolts. They need some serious ass, at least mine did.

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Caman96 said:

I hear ya. Getting my 5/8 to 177 lbs. kicked my a s s!

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Nad_Yvalhosert said:

I agree. I work in a suspension shop. We tighten them till the socket stops turning. Full max on my 1/2" gun is 1150 reverse, 900 forward. I suppose that means the u-bolts are somewhere around 800+ lb-ft.

And we don't get comebacks .

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Schurkey said:

These U-bolts are not like properly-made Grade 8 (or even Grade 5) bolts, hard and stiff with rolled threads.

They're semi-crappy mild steel, with cut threads instead of rolled threads. They require retorquing because they distort and lose tension.

I've got a hypothesis, that Nad can max-out his impact wrench on them (900 ft/lbs) and yet not actually achieve 900 ft/lbs because the thread friction becomes so great that the shank of the U-bolt acts like a torsion bar, absorbing the impacts without increasing the torque.

So, again--when it's me, I add anti-seize and then knock 20% off the specified torque. Less intestinal blow-out that way.

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