MM Torque Arm Pivot Bolt Torque Spec - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 01-31-2011, 04:37 PM Thread Starter
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MM Torque Arm Pivot Bolt Torque Spec

Installing the MM HD TA and the instructions say to torque the pivot bolt on the end with the urethan bushing to 220 ft-lbs. Seems a bit extreme for something that just holds the bushing on. The instructions also say you only need a 150 ft-lb torque wrench and that is what I have. Would it be ok to take it to just 150 ft-lbs instead of the 220?

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post #2 of 5 Old 02-01-2011, 08:12 AM
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You do realize that the bolt is what is keeping your axle from rotating, and therefore it needs to be on there tight?

Can't you borrow/rent a 250 ft-lb wrench?

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post #3 of 5 Old 02-01-2011, 12:49 PM
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Proper torque doesn't make a joint tighter. It's purpose is to keep the fastener from loosening. Not enough and the thing can vibrate loose. Most torque specs are based on fastener diameter, length, and thread pitch and are designed to stretch the fastener to almost it's yield point. The idea is the stretch loads the threads and locks them together.

Torque it to the recommended value. Locktite or some other way of guaranteeing the fastener doesn't work loose would be an excellent idea too.

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post #4 of 5 Old 02-03-2011, 05:01 PM Thread Starter
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Got a 250 ft-lb torque wrench and took the bolt to 220. Now I don't have to worry about it. Although, I can't imagine the bolt ever coming loose at 150 ft-lbs.
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post #5 of 5 Old 02-04-2011, 03:14 AM
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Ricky,

If that bolt was only tightened to 10lbs-ft of torque, then there would be very little pressure between the crush sleeve inside the bolt and the front of the TA.

When the engine applies torque to the rear axle, the nose of the TA tries to lift up. This is going to push the bottom surface of the crush sleeve against the face on the nose of the TA harder and pull the top of the crush sleeve away from the face of the nose on the front of the TA. When the bolt is torqued to only 10lbs-ft, it will only take a very small amount of engine torque to pull the crush sleeve off of the nose of the TA face at the top. As soon as this level of torque is reached, the bolt is now being bent by the torque at the rear axle. The bolt is going to fail very quickly.

The purpose of the fastener torque is to always keep the joint loaded in compression, even when tension and prying loads are counteracting the compression force.

If all of the compression load is counteracted by tension or prying loads, then the bolt will also come loose very easily.

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