New Screws Really Needed When Replacing Rotors?
Road Warrior
Joined: Sep 2008
Posts: 1,549
Likes: 8
From: North Texas
I've seen way too many rear pulley bolts shear off the rear wheel to not use new ones whenever the pulley gets removed and replaced.
I apply that same caution to brake rotors.
You can't see the damage that occurs to a bolt once it has been stretched by torque. We actually stretch bolts when we torque them, where in fact a torque spec itself is an indirect measurement of desired bolt stretch. Some bolts are sized and designed to be torqued and retorqued many times where they are never stretched beyond thier elasticity when torqued to required specs, but sometimes the spec'd torque takes them to their design limits where they are not intended to be reused by design.
You will find this with many modern auto engine head and rod bolts where the MOCO insists you use new bolts each time.
Myself, I play it safe and follow the MOCO's specs.
There are lots of invisible stresses generated on rotor bolts....Brake rotors get toutured by heat and rotating torque...When the rotor gets scalding hot it increases in thickness and places additional stretch on the bolts at their heads, then those hot stretched bolts are subjected to tremendous shear stress as the brakes are applied. A dragging brake often goes unnoticed where the rotor never gets a chance to cool between braking events and it enters those cycles at elevated temps placing even more stress on the head of those rather small screws.
Think about how often you apply especially the front brake and then imagine how many heat/stress cycles described above occur in the life of those bolts and maybe then you will do like suggested and toss the old ones in the trash.
Like you said, they are cheap, they are included and you already have them out......they are one small step from the trash can, huh?
I apply that same caution to brake rotors.
You can't see the damage that occurs to a bolt once it has been stretched by torque. We actually stretch bolts when we torque them, where in fact a torque spec itself is an indirect measurement of desired bolt stretch. Some bolts are sized and designed to be torqued and retorqued many times where they are never stretched beyond thier elasticity when torqued to required specs, but sometimes the spec'd torque takes them to their design limits where they are not intended to be reused by design.
You will find this with many modern auto engine head and rod bolts where the MOCO insists you use new bolts each time.
Myself, I play it safe and follow the MOCO's specs.
There are lots of invisible stresses generated on rotor bolts....Brake rotors get toutured by heat and rotating torque...When the rotor gets scalding hot it increases in thickness and places additional stretch on the bolts at their heads, then those hot stretched bolts are subjected to tremendous shear stress as the brakes are applied. A dragging brake often goes unnoticed where the rotor never gets a chance to cool between braking events and it enters those cycles at elevated temps placing even more stress on the head of those rather small screws.
Think about how often you apply especially the front brake and then imagine how many heat/stress cycles described above occur in the life of those bolts and maybe then you will do like suggested and toss the old ones in the trash.
Like you said, they are cheap, they are included and you already have them out......they are one small step from the trash can, huh?
Outstanding HDF Member
Joined: Jun 2008
Posts: 2,590
Likes: 6
From: Indiana
Grand HDF Member
Joined: Sep 2007
Posts: 4,122
Likes: 44
From: Boise Idaho
I have always reused the bolts as long as I clean them and clean the holes. Never made any sense to me that you would change a grade 8 bolt instead of changing and aluminum rim, which is going to give first.
I believe that 99% of the horror stories you hear are related to not torquing things properly.
I believe that 99% of the horror stories you hear are related to not torquing things properly.
Thread Starter
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Road Master
Joined: Oct 2008
Posts: 880
Likes: 81
From: California
Because the freakin' MoCo sells you chrome rotors with non-chrome fasteners, and then charges you more to get the matching fasteners! That's why.
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Frame/Suspension/Front End/Brakes
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Oct 5, 2006 12:34 PM
