I am replacing my lower ball joints and the torque specs list a three pass technique - first pass 15ft-lbs, second pass 210 degrees, third pass 52ft-lbs. I get the first and third pass, but is the second pass just an indication of how far to back off (loosen) before applying the final torque of 52 ft lbs?. It seems to me that if I torque to 15 ft lbs and then turn another 210 degrees clockwise, I would go way past 52 ft lbs. So is this trying to say you back off 210 degrees before the final torquing?

 

No, don’t back off. Keep tightening them

 

First pass Aligns

Second Turn 210 degrees Seats the Fastener

Third Final 52 ft lbs of Torque Stretches the the bolt

 

Very helpful. Might be a dumb question, but what do you do between passes? Tap the joint with a hammer, count to 30, have some coffee…..or what?

 

The torque then turn method is is a more accurate way of ensuring clamp load as torque can give a false reading - especially over used threads, oily threads, or when bringing parts like the cone shapes of the ball joint studs into contact. Instructing to torque to 100 lb/ft may give very different clamp loads across a something like a cylinder head, But a very light initial torque to set the parts, then a turn is always the same clamp load.
On the ball joint, the initial light torque sets the alignment and is low enough that the room for error and variance is very low. Gets the 2 cones of the bolt and spindle aligned.
Then the turn is always the same degrees - never a variance. This ensures that for some reason had the wrench clicked before their desired clamp load, there is no variance.
GM is then using a final torque to ensure it is at least that tight.

With this fastener in an aluminum spindle, this is not to stretch the bolt. You would damage the spindle before attempting a torque to yield on a bolt of this diameter in the aluminum.
It's just a more accurate method.

 

Ed is right. Another thing I'd like to point out is there are two different type fasteners that are often confused with each other. One is TTY, or torque to yield. The other is TTA, or torque to angle. Torque to angle fasteners can generally be reused. Torque to yield fasteners generally can not, because the material has "yielded," aka the elastic limit has been exceeded.....

 

Thanks grinder, didn't know that.

 

Very helpful, thanks - it just occurred to me that the second pass of 210 degrees might be without holding the spindle secure - in other words, letting the shaft turn in the aluminum to make sure it is seated, then continue with the third pass, once again holding the shaft steady. Does this sound right?