MotoIQ posted on June 15, 2017 15:01
Wrench Tip: Torquing Unreachable Fasteners
by Nikita Rushmanov
Have you ever looked at your service manual for a torque spec, only to curse, “What the hell were those engineers thinking?” We certainly have, but there is always a way to get things done by the book. The perfect example of an impossible torque spec is the driveshaft to differential flange on a 240sx. In this case, it’s impossible to get a socket on the nut because there is not enough room between the flange and the differential housing. Additionally, the hex head of the bolt on the other side is jammed against the flange, so you can’t torque that either. As a result of this, a lot of 240 owners we know never actually use a torque wrench on their driveshafts, instead opting to torque to “2 uga ugas” with an open ended wrench. To compliment this, we’ve also seen a few 240 driveshafts rattle loose, or in some cases, come off completely, punching holes in the floor pan.
So what’s the solution? You use a crowfoot wrench and some math. A crowfoot wrench is basically an open ended wrench that has a ⅜” or ½” square drive instead of a handle. This means that if you attach it to your torque wrench, you get an open ended torque wrench! You can pick up a set of crowfoots from Harbor Freight for as little as $10. However, there is one little caveat. Attaching that crowfoot changes the lever arm of your torque wrench, since the nut or bolt is no longer spinning on the same axis as the square drive of the torque wrench. We can compensate for this lever arm offset using math.
We usually use this Snapon torque wrench, which has a menu where you can enter your crowfoot offset, and it will automatically compensate. However, for this demo, we will use my “missile” Harbor Freight torque wrench.
So once you have the crowfoot, you need to know 4 things to calculate the new torque setting:

The target torque setting.

The length of the lever on your torque wrench.

The axis offset distance of your crowfoot.
 The angle of the crowfoot relative to the torque wrench.
The length of the lever is the distance between the axis of rotation of the square drive and the center of the handle. For this torque wrench, the distance is 11 inches.
To calculate the crowfoot offset, we usually take off the nut or bolt I’m torquing down and put it inside the crowfoot. This allows you to see where the axis of rotation is. For this 14mm crowfoot, the offset is 1 1/16 or 1.0625 inches.
The service manual calls for a torque spec of 2933 ftlbs, so our target torque setting is 30 ftlbs. For this particular application, we find it easiest if the crowfoot points straight, which means our crowfoot angle is zero. Now we have everything we need to calculate our new torque setting. For the calculations, we like to use this online calculator to make things easier.