Re: Torque Wrench Extension

[paul.heneghan@bbc.co.uk (Paul Heneghan)]

From: quk@sievers.com (Phil Payne)

>>This
>> works out to give you about 430ftlbs at the nut which is way outside the
>> range of most torque meters.

>The principle's right, but the maths is wrong.

>332 ft lbs at the nut.

We are obviously using different maths!  Here is my working (with my 
assumptions).

Torque = Force x Distance.

Manual says torque should be an indicated 258ftlbs (first assumption - I 
have seen some other figures mentioned, but this seems to be the most 
popular).

This torque is developed at the 1/2" square drive of the torque wrench.

Torque wrench is 1.5ft long (second assumption - many DIY TWs are this 
length, mine is slightly longer  - I don't know what the VAG one is.  This 
is a flaw in the maths of the person who thought up this way of specifying 
the torque - it depends entirely on the length of the TW which is not a 
constant).

To generate 258 ftlbs of torque, I am leaning with 172lbs force on the 
handle of the TW.  (172 x 1.5 = 258).

The torque developed at the crankshaft bolt is 172 x ( new length).  In this 
case, the new length is the length of the TW plus the length of the 
extension (part no. 2079).

I have been told the extension is 1ft long (third assumption - I've never 
seen one of these, but rumour has it that they are about 12" long and the 
pictures in the manuals seem to go along with this).

Torque at bolt = 172 x (1.5 + 1) = 430ftlbs.  QED

The only way your figure of 332ftlbs can be true is if the extension only 
adds 28% to the length of the TW.  This would give a TW which is 3.5ft long!

The longest TW I have seen is about 2ft long.  If VAG had meant this length 
to be used, then the torque multiplication factor would have been 3/2 which 
would give 387ftlbs at the bolt.

I think >400ftlbs is safe.

If anyone can spot a flaw in my maths, let me know!

(BTW, for the benefit of our American friends, VAG stands for Volkswagon 
Audi Group - one of the names of the Audi dealership over the years, 
probably similar to AoA)

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1989 Audi 100 Avant