Torque wrench problem

footman · 17 Nov 2008 at 09:13

I'm having problems engaging a wheel nut with my Halfords torque wrench because the wheel is recessed under the vehicle body (a trailer). I know I can fit an extension bar to the wrench but I seem to remember that it changes the torque imposed on the nut.

Is there a formula for calculating the new torque to be applied or another solution?

Firestar_3x · 17 Nov 2008 at 09:21

I was under the impression the amount of torque would only change if using something like a crowsfoot + Torque Wrench.

Since the extension bar is straight you are still applying the same amount of torque as if the socket was fitted directly onto the wrench (the pivot point hasn't actually changed), its only when you have offset items driven by the torque wrench the torque changes.

As an example:

The torque wrench measures the torque or twist applied at the pivot point or where you would normally put on a socket which is centered on the pivot point. The crowsfoot is about a 2 inch extension on the other side of the pivot point, so it torque reading on the wrench is not the same as applied to the nut or bolt.

footman · 17 Nov 2008 at 09:24

that makes sense, cheers.

Tesla · 17 Nov 2008 at 09:50

As you are not moving the pivot point the torque applied is not effected.

footman · 17 Nov 2008 at 09:55

cheers, off to Halfords to buy an extension bar and use my credit note!

slowrunner · 17 Nov 2008 at 12:01

With a good quality extension it'll be fine, the cheapo ones tend to have a bit of give in them, and twist a little under heavy torque, right at the end where it goes from round to square.

Dogbreath · 17 Nov 2008 at 12:07

slowrunner said:
With a good quality extension it'll be fine, the cheapo ones tend to have a bit of give in them, and twist a little under heavy torque, right at the end where it goes from round to square.

That doesn't change the amount of torque applied to the fastener though! Good quality extensions will last longer and take more torque before failure, but cheap ones won't affect the accuracy of a torque wrench,

slowrunner · 17 Nov 2008 at 13:10

True, but would be annoying if it gave way before the bolt was tightened to the correct torque!

Firestar_3x · 17 Nov 2008 at 13:15

Unless you buy a very cheap extension bar, or have a very large torque wrench i fail to see how using a extension bar on this is any different to anyother application using an extension bar and why it would be more prone to fail, buy quality items and it simply won't snap or twist.