Under swing arm brake and what went wrong

[Dendrob]

The blade version is a negative of the Storm one, (one has tang on sa, the other on the bracket) which is why you can't just swap brackets.
The device functions in two ways, allowing linear movement when you slide wheel spindle forward and back, and resisting the turning moment of the bracket when the brake is applied.
The standard design is strong as it's the shear strength of the weld on the tang or female part that would have to fail, and that has a large area and is only 10mm or so from the surface of the sa, so there's very little force trying to rotate the block welded to the sa. The force is directed vertically downward when the brake is applied.
With a rod type securing brace all of the tension is linear, and transferred directly to the mounting points both ends, assuming the rod itself is strong enough.
Hopefully the rod is directly lined up and not at an angle to the bikes front to back centreline, or that adds other problems.
But the mounting points both ends would be the key, as the parts you could bolt to aren't designed with this factored in- frame, footrest castings etc.
The tension created by the clamping force of the rear wheel spindle is nowhere near enough to hold it in place.

Personally, I wouldn't totally write off how much "help" the clamping force of the spindle nut brings to the party, but I must admit, on second thoughts, that if I were responsible for designing the assembly I'd disregard it completely, in the interests of designing something failsafe.

[fabiostar]

well after reading all that, i already have a blade swingarm to cut the brace off but i think il go down the route of modding the brace and keeping the standard storm brake setup..

[E.Marquez]

well after reading all that, i already have a blade swingarm to cut the brace off but i think il go down the route of modding the brace and keeping the standard storm brake setup..

If you want a above brake caliper set up, and a sturdy brace,, your already welding, weld on the fireblade caliper slider... Cutting into the brace to clear the SH caliper mount is really turning your brace from a functioning item to just for looks .. And if that's what your looking for, then fine., but otherwise use the fireblade caliper mount and slider.

[Dendrob]

Is the torque reaction fed into the far end of the fixed slider bolt? Wouldn't there be a large bending force applied to it and, even if the bolt were able to resist bending, the casting supporting the bolt looks pretty minimal. Additionally, the radius out from the wheel centreline isn't that great.

Surely by using the end of the bolt this way, you're increasing the load on the bolt more than double? Probably something like treble? Isn't the bolt already having to bear a proportion of the forces generated by braking and feeding them into the caliper bracket and then, with your set up, having to ADDITIONALLY cope with the total reaction load? All applied at a distance out (at the bolt head)?

I'm sorry, but I'm not the least bit surprised it failed! Sorry mate, but I'm just not.

We came up against the exact same dilemma on a special my brother is building and we agreed that we needed to make a bespoke caliper bracket. But because the sliding type calipers tend to have a complicated bracket, with some delicate tolerances, we opted for him to find either a caliper which had its own carrier plate or better still, find a suitable opposed piston type instead. That way the swinging bracket is kept simple. The project went on hold, but should be back on soon.

[E.Marquez]

Is the torque reaction fed into the far end of the fixed slider bolt? Wouldn't there be a large bending force applied to it and, even if the bolt were able to resist bending, the casting supporting the bolt looks pretty minimal. Additionally, the radius out from the wheel centreline isn't that great.

Surely by using the end of the bolt this way, you're increasing the load on the bolt more than double? Probably something like treble? Isn't the bolt already having to bear a proportion of the forces generated by braking and feeding them into the caliper bracket and then, with your set up, having to ADDITIONALLY cope with the total reaction load? All applied at a distance out (at the bolt head)?

I'm sorry, but I'm not the least bit surprised it failed! Sorry mate, but I'm just not.

We came up against the exact same dilemma on a special my brother is building and we agreed that we needed to make a bespoke caliper bracket. But because the sliding type calipers tend to have a complicated bracket, with some delicate tolerances, we opted for him to find either a caliper which had its own carrier plate or better still, find a suitable opposed piston type instead. That way the swinging bracket is kept simple. The project went on hold, but should be back on soon.

All good.... but of course it did not fail in any way you're concerned about.

Nor have the dozens of others that have done this exact mounting method.

It failed, simply because I used the worng material and dimensions of the strut rod// coupled with improper design of the insert.

I appreciate the feedback, thank you

[Dendrob]

All good.... but of course it did not fail in any way you're concerned about.

Nor have the dozens of others that have done this exact mounting method.

It failed, simply because I used the worng material and dimensions of the strut rod// coupled with improper design of the insert.

I appreciate the feedback, thank you

I apologise. You're a gentleman, thankfully. I should have thought more carefully about my post. I'm not convinced I'm right about the forces onto the bolt being added. I think maybe they're actually subtracted. Custard pie in face for me. Fire at will.

I'd appreciate your comments (on the engineering preferably, but also on my foolishness, should you be so inclined). I'm intrigued as to why the casting failed.

[Geordie]

Reading with interest.. My provisional plan is to do the bracing mod but fit a twin pot caliper like the brembo caliper from a Ducati which has the oil inlet hole orientated the same as the storms.. And get a custom bracket made up from Ali to locate it in the same position above the Swingarm. As the caliper isn't a sliding caliper the bracket should be much easier to manufacture from Ali plate.. Pads might have a deeper sweep than the disc radius if you catch my drift so may need modded too.. Plus I'm not sure the extra inboard width of the caliper would clear the wheel spokes.. Just an idea.. Any thoughts folks?! .. I hate sliding calipers.. Lol
It is good that you are discussing these things guys as it may serve to warn others.. It's exactly what forums are for. Glad there was no injuries. Geordie

[E.Marquez]

I'm intrigued as to why the casting failed.

I have only theory, no facts .. but after it broke and looking at how I mounted it, two things in my opinion led to the bracket failing the first time around (caliper mount casting the first time, strut rod the second time)
The casting failed because...
I cut the caliper bracket too far back (trimmed) leaving too little material remaining.
The original strut was too long, placing the caliper and bracket in a position that required the bracket to resist both a straight "pull" and a upward "pull" as forces were generated.
The second time around
Once I corrected the caliper location with a shorter strut rod, the cast bracket held just fine, and I moved the weak point to the incorrectly designed strut rod. Which failed quite spectacularly I might note due to the idiot that left too little cross section after adding a stainless steel insert to the rod to resist pulling threads from the aluminium rod.

[E.Marquez]

Reading with interest.. My provisional plan is to do the bracing mod but fit a twin pot caliper like the brembo caliper from a Ducati which has the oil inlet hole orientated the same as the storms.. And get a custom bracket made up from Ali to locate it in the same position above the Swingarm. As the caliper isn't a sliding caliper the bracket should be much easier to manufacture from Ali plate.. Pads might have a deeper sweep than the disc radius if you catch my drift so may need modded too.. Plus I'm not sure the extra inboard width of the caliper would clear the wheel spokes.. Just an idea.. Any thoughts folks?! .. I hate sliding calipers.. Lol
It is good that you are discussing these things guys as it may serve to warn others.. It's exactly what forums are for. Glad there was no injuries. Geordie

The long term plan is to use a rear caliper from a bike that has the caliper normally located under the swing arm so the bleeder is in the correct location and make a custom mount from solid billet of aluminum. with a designed built in strut rod mounting point that will be on center line of the part vice laterally quite a distance away as the current set up is, and closer to the rotation point around the axle. Both of those design changes will induce much less force on the strut rod by way of reduced leverage.

Though others have done so successfully I DO NOT recommend repurposing the OEM caliper bracket to a strut rod design, under swing arm mount.
I purchased a 14lb billet of aluminum just yesterday to machine my new caliper mount from.