[DML] Re: More TAB nonsense

[tobyp@xxxxxxxxxxxx]

Rich - Since nobody else has chimed in on this question, I'll give 
it a shot.  When a bolt is "slathered with anti-seize compound", you 
can consider it a lubricated bolt.  That means that you will get 
more stretch on the bolt for the same amount of torque as compared 
to torqueing up a dry bolt.  A ballpark estimate for the difference 
in this case would be that the "effective torque" on the TAB could 
be as high as 90 ft-lbs, assuming that he torqued the lubed bolt to 
55 ft-lbs indicated on the wrench.  Many anti-sieze compounds don't 
have quite the lubricity as grease, so it may be a bit lower.  This 
estimate comes from charts in my aerospace design manual.  Using 
some of those icky engineering formulas, that 90 ft-lb torque would 
apply about 24,000 pound tensile load to the bolt.  In side-by-side 
tensile testing of the TOBY-TAB to the stock bolt, the stock bolt 
began to yield at about 22,000 pounds (I can send you the charts if 
you want them).  That means that your new bolt could be pretty close 
to yielding.  I won't go so far as to say that it is yielded, but 
you're definitely up there in range of the top of the curve.  The 
other concern in this case are the steel sleeves through the bushing 
and the trailing arm.  The compressive stresses on the edges of the 
sleeves are very high (lots of pounds, but very few square inches of 
area = high PSI).  I think that high compressive stresses on the 
sleeves are better than a loose joint caused by a yielded bolt, so I 
would back it off to about 45 ft-lbs to get the bolt down below it's 
yield point. I am using some conservatism in my numbers, so I think 
that would be fine.  Let me know if you have any questions about 
this.

Toby Peterson  VIN 2248 "Winged1"
DeLorean Parts Northwest, LLC
www.delorean-parts.com


-- In dmcnews@xxxxxxxxxxxxxxx, "cruznmd" <racuti1@xxxx> wrote:
> In response to Dave T's last post regarding proper TAB procedures,
> I'd like to say that
> 
> A) I made sure the mechanic knew to torque down with the full 
weight on the suspension. He did this correctly.
> B) Heat was only applied to the trailing arm when it was out of 
the vehicle. The bushing was not heated.
> C) The one thing he did that concerned me, was slather everything 
in anti-sieze.
> 
> How far off are the torque readings if you apply anti-sieze? How 
> concerned should I be?





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