if torque values are dependent on the bolt/nut, why do we have diff values for diff applications

[jalikaria24]

not sure iff this is correct or incorrect but i was always told the torque value that was listed in a manual or whatever is the value that the bolt is supposed to be tightened too. any less and it could fall off, and any more and you could ruin the bolt/nut etc etc.

however for example for a axle nut, we have the same axel nut be used on various gm applications, i see between 155 foot lbs 173 foot lbs and 177 foot lbs

why is there a difference?
or is the difference between 155 foot lbs and 177 foot lbs insignificant anyways? like a 1/4 turn more or something?

thx

 

[Racecarfan2]

You are adjusting bearing preload, The tighter the nut the closer the tolerance is. The preload can even change by application with the same part number bearing based on gross vehicle weight and intended use.

 

[jalikaria24]

You are adjusting bearing preload, The tighter the nut the closer the tolerance is. The preload can even change by application with the same part number bearing based on gross vehicle weight and intended use.

ahh gotcha so would you say we have some leeway then or needs to be exact for the application?

 

[wpod]

I am wondering is the A&P on this site will chime in,, They know stuff.

 

[Racecarfan2]

ahh gotcha so would you say we have some leeway then or needs to be exact for the application?

You see a published torque spec, the engineers drawings probably have an acceptable range, The torque on a new Nut on A new Axle on a New Car is much easier to measure as all of the variables are known. You throw in temperature, rust, wear and tear, calibration of tools etc. Torque is never going to be exact on the used piece.

 

[joegreen]

Well fasteners will have a torque spec for themselves showing where there maximum clamping force is without deforming the fastener. Sometimes parts will require less torque than what the fastener can provide because the part will get crushed ECT.

 

[ABN_CBT_ENGR]

Short class here

A torque spec ( when given) is for the joint- not the fastener. (many times a fasteners max torque will damage a joint, especially with bearings, seals and gaskets)

Someone came up with clamping forces necessary and did whatever testing and came up with a torque spec that will put acceptable tension within a range on a joint.

Torque is commonly used because in probably 97% of all mechanical joints it will be adequate.

The rest use UT, strain gauges, eddy currents, thread count etc to pull actual tension

This is the extremely short text version

 

[kschachn]

Thank you, yes it is clamping force. And fastener torque is a particularly ineffective way of gauging that but it is convenient and easy. It does make me laugh sometimes when I see these expensive digital torque wrenches that have high resolution displays, as long as the wrench is accurate any wrench will be adequate.

 

[doitmyself]

apollo18, if you are interested in this stuff, Google "torque error" and similar topics to gain some background information about the process. This site will give you an introduction: https://surebolt.com/index.htm But don't go overboard. As stated above, torque wrenching is far from perfect, but is good enough in many applications. Eliminating as many errors as possible is a good goal.

I really think that many people think that using a certain tool automatically results in the correct result. It doesn't. On Youtube, you often see people pull a torque wrench until it clicks, then pull it again one or more times to cause it to click over and over. Torque wrenching and crimping are both misunderstood by many.

Have fun learning all this stuff!

 

[Yah-Tah-Hey]

I am wondering is the A&P on this site will chime in,, They know stuff.

Some do, some don't.