Ubolt nuts???
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Joined: Sep 2009
Posts: 117
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From: Colorado
Sorry about that. I will try again in English with a bit more info.
The U-bolts clamp or compress the leaf springs, top plate, block, axle seat and axle together.
Manufacturers spec torque and not clamping load because it is a much easier measurement. The aim is to compress everything sufficiently to prevent the axle from falling off and to keep the leaf springs from failing which could result in the axle falling off. The weakest point of the spring is at the centerbolt. Proper compression (clamping force) keeps the springs from flexing in the centerbolt area. In other words there should be no flexing at the weakest point of the spring. Moreover, horizontal forces which could sheer the centerbolt are reduced. Oh and proper clamping force also impacts spring stiffness and thus vehicle handling etc.
Now if torque is the way we attempt to set the clamping force we need to optimize the conditions. After the first reuse a nut and bolt combo may require 35% more torque to achieve the same clamping force. If the U-bolt stretches when you tighten the nuts, there is strain placed on the threads of the nut. Most of the strain is on the first few threads (about 78%). This can change their shape. If their shape is different, when you go to reuse them friction will be more or less than is expected and thus the torque measurement will no longer be a good way of achieving the needed clamping force. By the way corrosion can alter friction as well.
It comes down to this, is the cost of 8 nuts worth the risk of failure. In some cases the answer is yes. Here failure could be catastrophic so I would buy the nuts.
The U-bolts clamp or compress the leaf springs, top plate, block, axle seat and axle together.
Manufacturers spec torque and not clamping load because it is a much easier measurement. The aim is to compress everything sufficiently to prevent the axle from falling off and to keep the leaf springs from failing which could result in the axle falling off. The weakest point of the spring is at the centerbolt. Proper compression (clamping force) keeps the springs from flexing in the centerbolt area. In other words there should be no flexing at the weakest point of the spring. Moreover, horizontal forces which could sheer the centerbolt are reduced. Oh and proper clamping force also impacts spring stiffness and thus vehicle handling etc.
Now if torque is the way we attempt to set the clamping force we need to optimize the conditions. After the first reuse a nut and bolt combo may require 35% more torque to achieve the same clamping force. If the U-bolt stretches when you tighten the nuts, there is strain placed on the threads of the nut. Most of the strain is on the first few threads (about 78%). This can change their shape. If their shape is different, when you go to reuse them friction will be more or less than is expected and thus the torque measurement will no longer be a good way of achieving the needed clamping force. By the way corrosion can alter friction as well.
It comes down to this, is the cost of 8 nuts worth the risk of failure. In some cases the answer is yes. Here failure could be catastrophic so I would buy the nuts.
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timbersteel
1987 - 1996 F150 & Larger F-Series Trucks
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Jul 26, 2005 02:03 AM
