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Cracking ball joints

Thursday 4 January 2018

Today I was dismantling the suspension of my Triumph spitfire. This involves removing several ball joints. A ball joint has a tapered end that fits tightly into a hole, removing them is difficult so you need a ball joint cracker. This fits between the ball joint and the holding arm, you tighten the nut and the ball joint pops off. Today I had a bit of a shock when a ball joint flew off suddenly at great speed. I should have known it would since I was doing a lot of work tightening up the bolt storing PE in the joint that was converted to KE when it is released.

Let´s say I was exerting 300 N over the last half turn with a 20 cm long spanner. Work done = Torque x angle = 300 x 0.2 x π =190 J. The ball joint weighs about 200g So it´s velocity can be found from 1/2mv2 that gives 44 ms-1 which is 160 kmhr-1 . That´s why it´s best to crack them while they are still attached to something. To be honest I think my estimate is a bit high, a lot of energy will be lost in friction.

Mock exam
21 Jan 2018


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