How Tight is 200nM + 180 degrees?

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2008 VW Passat 2.0T

The repair manual specified 200nM (148 ft lbs) plus 180 degrees for the front axle bolt. This car calls for the Type B bolt without the ribs. The updated axle bolt is a 24mm twelve-point bolt with a pre-applied red threadlocker. Per VW, it is one-time use.

I think this may be a TTY bolt.

In terms of "actual force exerted," what does 148 ft lbs plus 180 degrees actually amount to? 300 ft-lbs? 400 ft-lbs? I used a 5' long breaker bar plus my body weight (230 lbs) and it was not easy to get the bolt to turn 180 degrees...but I did it.

Here's a picture of the bolt in question.



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Depends on thread pitch. If times past count, the old VW axel torque was 600Ft/lbs if I recall. Gooten tight.
Smoky
 
The spec may be to preload the bearings properly. With many bearing hub unit designs the proper axle nut torque is critical for proper bearing preload.

Also, the bolt doesn't have the smooth shank that is narrower than the threads. This suggests it is not a TTY bolt and is a one time use because of the locktite.
 
The 148 ftlbs takes out the slack in the assembly.

The 180 degrees sets the bolt stretch.

Bolt stretch exerts the clamping force that the engineers specified.

With the thread pitch and bolt size, an engineer could estimate the clamping force of that bolt. I imagine it to be in the few thousand pound range.
 
Originally Posted by The Critic
I used a 5' long breaker bar plus my body weight (230 lbs) and it was not easy to get the bolt to turn 180 degrees...but I did it.



Maybe get a torque multiplier if you do this often?
 
Originally Posted by The Critic
In terms of "actual force exerted," what does 148 ft lbs plus 180 degrees actually amount to? 300 ft-lbs? 400 ft-lbs? I used a 5' long breaker bar plus my body weight (230 lbs) and it was not easy to get the bolt to turn 180 degrees...but I did it.

It doesn't equate to any "actual force exerted" or friction torque, since you're tightening the bolt past the yield point (yes, it's a TTY bolt). That said, the reason for using angle torque is that "force exerted on the bolt" is very imprecise in determining bolt tension. That's the whole point of using angle torque.

This does a good job of explaining it: http://www.boltscience.com/pages/a-case-study-in-torque-angle-tightening.pdf

Bickford's book goes into this in greater detail, if you really like to geek out on this stuff. It's the seminal text on the subject:
https://www.amazon.com/Introduction-Design-Behavior-Mechanical-Engineering/dp/0824792971

One interesting note there is the yield strength graph on re-used TTY fasteners. I totally understand why manufacturers call for these to never be reused, but the reality is that a TTY fastener reused once is generally stronger than a new one.
 
I did the same on my car, max out the torque wrench and then crank the bejeezus out of it. I think mine was only 90 degrees though.

I'd rather not have to purchase a 3/4 or 1 inch torque wrench just to do axle nuts. Cranking something to a confirmed 5-600 ft/lbs would make you feel really strong though.
 
Torque is the 3rd-best way of setting bolt clamp force. Friction on the head underside and in the threads is too variable to get much better than +/-15% clamp load.
Turn-angle is much better for accuracy. There is still inaccuracy in measuring turn angle, as most mechanics make marks with a Sharpie, then eyeball the turn angle.
Direct measurement of stretch is best of all. But expensive and impractical for many situations.
 
The 200 NM is to preload the bearing. The 180 degrees is to stretch the bolt. Often the the torque applied doesn't increase verry much when you stretch the bolt. And although it is not something the engineers wan't you to do. There is nothing wrong with doing the 180 degrees with an impact gun.
 
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