Torque Wrenches - my answer...

[SJ]

You got it right.
I was at this same point before, yet 2 + 2 wasnt coming out to 4.

You are missing two critical parts of the puzzle.
In the first case where you use tool 2079, you know what the applied torque
is > 285 ft lbs. This number is stated in the manual . .  . . a documented
fact.
But you are missing the the first critical part . .what was the original
torque wrench length? That makes a difference in the final torque at the
bolt. The difference between using my wrench(1.45 ft) and Huw's BigMotha(3.5
ft) is 100 ft lbs . . . not exactly chump change.

In your second case, you add an extension to the end of a click type torque
wrench (Adding extension to beam type wrench wont work), and you drive the
bolt directly(not using tool 2079). You are assuming the second critical
part . . that you know what the final bolt torque is supposed to be. What do
you set the torque wrench to?  Is there a number for this bolt in any
manual? And no, you cant derive this number knowing 285 ft lbs because you
dont know the original torque wrench length. A conundrum.

As Ameer pointed out, everyone got it right about the tool, and the use of
different extensions, and the basic torque formula. The difficulty was that
we did not realize how important the torque wrench length was to the
discussion. The other difficulty was an assumption that the torque at the
bolt is 340 ft lbs. Everytime someone came up with a different number, the
others thought that he did not understand the basic leverage theory . . .and
the explanations continued.

At the beginning of this discussion, what we all did not know(I mean
documented fact) is what the final bolt torque is supposed to be.
At the end of this discussion, we still dont know the "official" final bolt
torque value.
All the other pieces of this puzzle would have fallen neatly into place.
Well, almost . .as long as we also understand the impact of the wrench
length on setting the torque for tool 2079 . . . its only 285 ft lbs if you
have the original torque wrench in your hands.


SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q


> From: Ameer Antar <antar at comcast.net>
> Subject: Re: Torque Wrenches - my answer...
> To: quattro at audifans.com
>
> I thought about this for a while and I think I've figured out the
discrepancy. I'm sure whatever recommendations for the proper torque are
good, but I can see that some listers are actually concerned about figuring
out the right number. Anyway, I think actually the 2 camps on this issue
both have it right, it just depends on the situation. The difference lies in
where you place the extension. An extension used w/ a torque wrench will
always increase torque on the bolt and reduce the necessary force to be
applied at the other end. In essence it makes it easier (less force needed)
for the person to turn the bolt. The position of the extension is what
determines where the torque multiplication begins. If you have the extension
at the front of t-wrench, then the extension makes it easier for the wrench
to turn the bolt. That makes the reading on the torque wrench less than what
is actually being transmitted to the bolt. Of course this also lessens the
effort of the mechanic turning it b/c of the increased total length. There
is no way that using the 2079 as indicated would result in the same torque
at the bolt as at the torque wrench head. This is reinforced by the caution
in the Bentley which states, "Tightening torque applies only when extension
tool 2079 is used...". So that means the use of the tool definitely affects
the torque reading and the torque therefore will be different at the head of
the wrench and at the bolt.
>
> The other method used is to add a bar to the end of the wrench. The head
of the wrench directly drives the bolt head, but the extension allows the
user to use less force at the further distance. So instead of the extension
making it easier for the torque wrench to turn the bolt as in the above
paragraph, this method makes it easier for the person to get to the proper
torque. The reading of the torque wrench will be accurate in this case, b/c
it directly drives the bolt. Most likely, the reason torque wrenches have
warnings about using extensions on the end is that they can be easily
damaged if over-torqued and also they loose accuracy b/c of the play usually
found in that setup. If you're going to bother to torque a bolt, you might
as well use the right wrench for that range. The only way to accurately
increase (aka multiply) the torque of these wrenches is to use an extension
at the front, so that the torque wrench will still be in it's designed range
yet be able to apply mo
>  re torque to the bolt.
>
> In essence, both camps are right, it just depends on what setup you're
using. Also the person who mentioned the fact that the wrench and extension
should be in a straight line is correct. In any Physics book you'll find
that a force which is not exerted at right angle to the torque arm, will not
exhibit the maximum torque at the pivot. You have to use trigonometry to
figure the exact numbers. I know somebody who's a Physics grad student, so
hopefully I'll have him straighten this out for us even further.
>
> -Ameer