Brake work = back to Physics class
Thread Starter
Racer
Joined: Aug 2002
Posts: 396
Likes: 1
From: East Hampton CT
Brake work = back to Physics class
I've read a lot of threads on the subject of how to loosen the brake caliper bracket bolts.
I performed some brake work this weekend myself. I had difficulties removing these bolts, so I got to thinking back to my Physics class in college.
Torque is measured in foot-pounds. The formula for torque is
Torque = distance x force
Let's figure out the force required if using 10" long 1/2" drive ratchet to remove the caliper bolt torqued to 125ft-lbs.
force = Torque/distance = 125/(10"/12") = 150 lbs.
No wonder they can't be freed using this method. I don't care if you are Arnold.
OK, let's try a 18" breaker bar.
force = 125/(18"/12") = 83.33 lbs
Much easier. However, I haven't taken into account the thread lock on the bolt when torqued at the factory, but it can be done.
A 24" breaker bar can make life much easier.
force = 125/(24"/12") = 62.5 lbs
After taking with a mechanical engineer here at work, he offered another interesting insight. To calculate the amount of force experienced by the head of the bolt, use the following formula.
Torque = (friction of mating surface) x (diameter of bolt) x Force
The mechanical handbook says to use 0.2 as a general friction coefficient if it is not known.
Applying the formula
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
Therefore,
F = 125/(0.2 x 1/2") = 1250 lbs.
No wonder GM recommends replacing these bolts when remounting the caliper brackets.
I performed some brake work this weekend myself. I had difficulties removing these bolts, so I got to thinking back to my Physics class in college.
Torque is measured in foot-pounds. The formula for torque is
Torque = distance x force
Let's figure out the force required if using 10" long 1/2" drive ratchet to remove the caliper bolt torqued to 125ft-lbs.
force = Torque/distance = 125/(10"/12") = 150 lbs.
No wonder they can't be freed using this method. I don't care if you are Arnold.
OK, let's try a 18" breaker bar.
force = 125/(18"/12") = 83.33 lbs
Much easier. However, I haven't taken into account the thread lock on the bolt when torqued at the factory, but it can be done.
A 24" breaker bar can make life much easier.
force = 125/(24"/12") = 62.5 lbs
After taking with a mechanical engineer here at work, he offered another interesting insight. To calculate the amount of force experienced by the head of the bolt, use the following formula.
Torque = (friction of mating surface) x (diameter of bolt) x Force
The mechanical handbook says to use 0.2 as a general friction coefficient if it is not known.
Applying the formula
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
Therefore,
F = 125/(0.2 x 1/2") = 1250 lbs.
No wonder GM recommends replacing these bolts when remounting the caliper brackets.
Pro
Joined: Dec 2003
Posts: 563
Likes: 0
From: Albuquerque NM
Originally Posted by HeadsUp
I've read a lot of threads on the subject of how to loosen the brake caliper bracket bolts.
I performed some brake work this weekend myself. I had difficulties removing these bolts, so I got to thinking back to my Physics class in college.
Torque is measured in foot-pounds. The formula for torque is
Torque = distance x force
Let's figure out the force required if using 10" long 1/2" drive ratchet to remove the caliper bolt torqued to 125ft-lbs.
force = Torque/distance = 125/(10"/12") = 150 lbs.
No wonder they can't be freed using this method. I don't care if you are Arnold.
OK, let's try a 18" breaker bar.
force = 125/(18"/12") = 83.33 lbs
Much easier. However, I haven't taken into account the thread lock on the bolt when torqued at the factory, but it can be done.
A 24" breaker bar can make life much easier.
force = 125/(24"/12") = 62.5 lbs
After taking with a mechanical engineer here at work, he offered another interesting insight. To calculate the amount of force experienced by the head of the bolt, use the following formula.
Torque = (friction of mating surface) x (diameter of bolt) x Force
The mechanical handbook says to use 0.2 as a general friction coefficient if it is not known.
Applying the formula
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
Therefore,
F = 125/(0.2 x 1/2") = 1250 lbs.
No wonder GM recommends replacing these bolts when remounting the caliper brackets.
I performed some brake work this weekend myself. I had difficulties removing these bolts, so I got to thinking back to my Physics class in college.
Torque is measured in foot-pounds. The formula for torque is
Torque = distance x force
Let's figure out the force required if using 10" long 1/2" drive ratchet to remove the caliper bolt torqued to 125ft-lbs.
force = Torque/distance = 125/(10"/12") = 150 lbs.
No wonder they can't be freed using this method. I don't care if you are Arnold.
OK, let's try a 18" breaker bar.
force = 125/(18"/12") = 83.33 lbs
Much easier. However, I haven't taken into account the thread lock on the bolt when torqued at the factory, but it can be done.
A 24" breaker bar can make life much easier.
force = 125/(24"/12") = 62.5 lbs
After taking with a mechanical engineer here at work, he offered another interesting insight. To calculate the amount of force experienced by the head of the bolt, use the following formula.
Torque = (friction of mating surface) x (diameter of bolt) x Force
The mechanical handbook says to use 0.2 as a general friction coefficient if it is not known.
Applying the formula
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
Therefore,
F = 125/(0.2 x 1/2") = 1250 lbs.
No wonder GM recommends replacing these bolts when remounting the caliper brackets.
Team Owner
Joined: Aug 2003
Posts: 24,333
Likes: 1
From: VA
St. Jude Donor '03-'11
Actually, the only reason GM recommends replacement is because the replacement bolts come with loctite (or it's equivalant) on the bolt.
You can just clean the threads and reuse the bolt.
I was worried about the same thing, and if you think about it, why would they use an undersized bolt that would be stretched to the point that it's unusable when torqued to spec?
You can just clean the threads and reuse the bolt.
I was worried about the same thing, and if you think about it, why would they use an undersized bolt that would be stretched to the point that it's unusable when torqued to spec?
Race Director
Joined: Dec 2000
Posts: 19,304
Likes: 85
From: San Diego CA
First of all, torque units should be referred to with the force units first and then the distance units. lbs-ft is correct, ft-lbs is not.
Secondly, the formula you listed as:
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
is commonly used to determine torque based upon the tension induced in the bolt. The force measurement you came up with is actually bolt tension, not the amount of force you need to apply at the end of a breaker-bar.
Also, there is such a thing as "breakaway torque" and some studies show that although it is higher than the installation torque, it is not genarally significantly higher unless corrosion is severe.
Secondly, the formula you listed as:
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
is commonly used to determine torque based upon the tension induced in the bolt. The force measurement you came up with is actually bolt tension, not the amount of force you need to apply at the end of a breaker-bar.
Also, there is such a thing as "breakaway torque" and some studies show that although it is higher than the installation torque, it is not genarally significantly higher unless corrosion is severe.
Thread Starter
Racer
Joined: Aug 2002
Posts: 396
Likes: 1
From: East Hampton CT
Originally Posted by Dave68
First of all, torque units should be referred to with the force units first and then the distance units. lbs-ft is correct, ft-lbs is not.
Secondly, the formula you listed as:
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
is commonly used to determine torque based upon the tension induced in the bolt. The force measurement you came up with is actually bolt tension, not the amount of force you need to apply at the end of a breaker-bar.
Also, there is such a thing as "breakaway torque" and some studies show that although it is higher than the installation torque, it is not genarally significantly higher unless corrosion is severe.
Secondly, the formula you listed as:
125 ft-lbs = (0.2) x (1/2") x F (1/2" estimated bolt diameter)
is commonly used to determine torque based upon the tension induced in the bolt. The force measurement you came up with is actually bolt tension, not the amount of force you need to apply at the end of a breaker-bar.
Also, there is such a thing as "breakaway torque" and some studies show that although it is higher than the installation torque, it is not genarally significantly higher unless corrosion is severe.
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Race Director
Joined: Dec 2000
Posts: 19,304
Likes: 85
From: San Diego CA
Hey, with a long enough steel tube, you can move the world! Come to think of it, I used my small hydraulic floor jack many times when breaking loose stubborn, rusted bolts in my 68 C3's suspension. Those floor jacks are very handy tools!
Thread Starter
Racer
Joined: Aug 2002
Posts: 396
Likes: 1
From: East Hampton CT
Originally Posted by Dave68
Hey, with a long enough steel tube, you can move the world! Come to think of it, I used my small hydraulic floor jack many times when breaking loose stubborn, rusted bolts in my 68 C3's suspension. Those floor jacks are very handy tools!
