Torque Multiplier

Tech > Torque multiplier


The yoke bolts on our ProPride 3P hitch require 250 ft-lbs of torque. My current torque wrench maxes out at 150 ft-lbs, but there's an alternative to buying a bigger wrench: a torque multiplier. I got mine at Princess Auto (Part No. 8063927):

input side

On one side there's a 1/2" square socket where the torque wrench connects. One the other side is a 3/4" drive to which the appropriately-size socket connects. Inside the hub of the torque multiplier is a 4:1 reduction planetary gear set... so every complete revolution of the torque wrench generates one quarter revolution of the socket.

What appears to be a handle on the torque multiplier is called a reaction bar. Applying torque to the torque multiplier would make the planetary gears counter-rotate if the reaction bar was not placed against a solid surface (such as pavement). When it is, the planetary gears are forced to rotate around the sun gear, generating the reduction.

Here's how it's used.

Torque multiplier use (4:1 reduction)

The appropriate size of socket (not depicted) is attached to the output drive of the torque multiplier (red). The reduction bar is placed on the ground to the left for clockwise torque application, and the torque wrench (blue) is attached to the torque multiplier.

I thought the torque wrench would be set to 1/4 of the torque specification, but such is not the case. There's a torque ratio that doesn't quite correspond to the reduction gearing - on this wrench the ratio is 1:3.33. So by dividing the torque spec by 3.33 I got the wrench setting. For 250 ft-lbs, it was 75.

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