brake disc removal

[dlaing]

The following concerns the bolts that hold the caliper together, but the same should hold true about the mounting bolts. Although strength is important, you just have to surpass exceptable strength, not reach maximum strength.

As a point of academic interest there is no advantage to using an extremely high tensile bolt in this application – again, we are looking for stiffness, not strength. Stiffness is a function of the material's modulus of elasticity and all steels have the same elastic modulus (about 207 gigapascals per cubic millimeter or Gpa.

http://www.stoptech.com/tech_info/wp_monobloc.shtml

Lots of other good stuff there, maybe even the answer to what is the optimum bolt?

[docc]

I'm thinking the forces pushing the caliper apart are hydraulic, perhaps aided by heat, but the forces on the mounting bolts for both the caliper and the rotor are a function of speed, mass and braking force perhaps multiplied by the torque moments separating the fastening point from the point of rotation and the point of traction. Lot's more force on the mounting than simply holding the caliper together.

[Guest ratchethack]

The waters are getting deeper, Gents. I fear we are rapidly getting in over our heads and beyond the scope of wot makes sense to discuss here, lest we gain some qualified ME input very quickly (and o' course that counts me OUT).

 

However, I will add by way of possible clarification that Dave's quote from the link at stoptech.com above brings out an important point, and another example of why grading of fasteners on brake parts is non-trivial, and why one should NEVER replace brake fasteners without understanding the critical requirements and NEVER down-rate them accordingly.

 

Unlike caliper mounting bolts, which, in the case of our as-issued non-radial Brembo's, must handle extreme yield (shear) loads without virtually any requirement for tensile loads, the bolts that hold a brake caliper together against hydraulic forces of thousands of PSI require relatively low yield (shear) strength, nor is tensile strength the key parameter here. It's STIFFNESS of the bolts, or resistance to stretch under extreme load that is critical. A high tensile strength bolt here may well hold up perfectly under the pressures encountered without failing, but if it stretches under load, brake feel will be lost, not to mention brake effectiveness, and ultimately failure of the caliper from separation and leakage.

[dlaing]

I agree, as those bolts are taking half the vector force that the carrier bolts are taking, assuming friction is evenly balanced between pads. Plus they are taking the hydraulic load, but that can't be all that much considering the strength of our hand. What is the leverage ratio?

Yet, they are still concerned about the rigidity.

It seems to me, the rigidity of the mounting bolts would be even more important than the rigidity of the clam shell bolts.

Should I stop speculating before Ratchet gets all tied up in a knot again?

EDIT Ooops too late, I missed the last post. "The waters are getting deeper, Gents. "

[Guest ratchethack]

. . .those bolts . . .are taking the hydraulic load, but that can't be all that much considering the strength of our hand. What is the leverage ratio?

Dave, I don't know the numbers, but I b'lieve you'll find that you can deliver into the hundreds of thousands of pounds of PSI force in brake calipers against the rotor with your hand.

 

EDIT: I just checked. The front Brembo caliper halves are joined by two Metric Class 10.9 bolts. Each is rated at 136,000 PSI tensile strength. So the bolts in each caliper of the fronts can handle up to 272,000 PSI.

 

Ever use a bottle jack to lift your Guzzi -- or better yet, a car? This is the leverage strength of hydraulics possible with just your arm. It's exactly the same principle at work.

[Dan M]

Dave, I don't know the numbers, but I b'lieve you'll find that you can deliver into the dozens of thousands, and possibly hundreds of thousands of pounds of PSI force in brake calipers against the rotor with your hand.

 

Ever use a bottle jack to lift your Guzzi -- or better yet, a car? This is the leverage strength of hydraulics possible with just your arm. It's exactly the same principle at work.

 

You would have to know the piston sizes of the master and the calipers, ratio of the hand lever (which is pretty big, maybe 10:1 and then do the math, but as Ratch said the PSI is in the thousands, although I doubt it is much more than a few thousand on each rotor.

 

I fear we are rapidly getting in over our heads and beyond the scope of wot makes sense to discuss here

 

Really? Now you are saying that?

[docc]

 

 

EDIT: I just checked. The front Brembo caliper halves are joined by two Metric Class 10.9 bolts. Each is rated at 136,000 PSI tensile strength. So the bolts in each caliper of the fronts can handle up to 272,000 PSI.

 

 

How is it we can figure this out , but not be able to determine the actual specification of the bolts holding the rotor to the wheel??

[Guest ratchethack]

I take it back with apologies. My mistake.

 

Here's where I'm starting to get in over me head as previously hinted.

 

Since the unit of measure is PSI, it doesn't double with two bolts. (I think? -- Where's our resident ME's?!)

 

So I b'lieve it's "only" 136,000 PSI in the caliper that the bolts in each of the front Brembo calipers have to handle.

[emry]

Not to throw a stone in the works, but lets not forget what that magic "psi" means. Pounds per Square Inch. When used to describe a material a sample is a "square inch" Our bolts are neither square nor are they one inch. You would need to calculate the area of the bolts an use that as a percent of the total.

[dlaing]

So, is that more or less than the force that mounting bolts have to endure during a nose wheelie?

And which is stronger, four M8 bolts or two M10?

Interestingly my Ducati999 calipers apparently have 3 not 4 M8 pinch bolts.

Although it has only 3 bolts, the multi-pad design allows for a centered bolt.

 

 

In any case, what holds true in the need for rigidity in the pinch bolts also holds true for the mounting bolts.

Maybe more so, or maybe less so.

The important thing when shopping is to look for rigidity, if you can determine it...

[dlaing]

EDIT: I just checked. The front Brembo caliper halves are joined by two Metric Class 10.9 bolts. Each is rated at 136,000 PSI tensile strength. So the bolts in each caliper of the fronts can handle up to 272,000 PSI.

Actually four bolts join the two halves.

[Guest ratchethack]

Actually four bolts join the two halves.

Right you are, Dave. I stand corrected.

 

I thought we had some ME Guzzisti at one point. A certain element of such types seem to be irrepressibly attracted to the Guzzi. After all the flopping about with bolt tensile, yield, stiffness and vector analysis in this thread, I would've also thought this would tend to draw 'em out o' the woodwork for some enlightenment.

 

Could it be we have none??

[mike wilson]

At this point, I hesitate to mention stainless steel spokes.

 

 

 

 

 

 

 

 

 

Oh dear, I just have........ 8-)))

 

 

 

 

I do have a ME qualification but would not call myself any sort of pro.

[Guest ratchethack]

I do have a ME qualification but would not call myself any sort of pro.

Outstanding, Mike! You had me wondering. . .

At this point, I hesitate to mention stainless steel spokes.

But wye the hesitation, my friend?!

 

C'mon in, the water's fine -- once you get used to it. . .

 

I've laced, unlaced, replaced countless broken spokes, scrounged for new & "breaker-yard fresh" matching spoke-head angles, and re-laced a variety of spoked wheels in my day, and "upgraded" stock spokes with stainless. The trade-off considerations between carbon steel and stainless spokes are much the same as with fasteners, as I reckon most anyone might expect. The principles at work are much the same. After all, spokes are more or less simply very long fasteners, n'est-ce pas?

[JoeV11]

EDIT: I just checked. The front Brembo caliper halves are joined by two Metric Class 10.9 bolts. Each is rated at 136,000 PSI tensile strength. So the bolts in each caliper of the fronts can handle up to 272,000 PSI.

Whoa now - the 136,000 psi is pounds per square inch of bolt not psi of hydraulics. But brake lines can go over 10,000 psi during panic stops. That times the area of four or six pistons is a lot of force trying to blow the caliper apart! Joe