Under swing arm brake and what went wrong
Under swing arm brake and what went wrong
Under swing arm brake.....what went wrong?....Lots, in two stages, the end result was a trashed bike, 4 broken ribs, ruined gear head to toe.
The idea came from a bloke on this very forum... rotate the brake caliper down using a stock caliper mount, and a strut mounted to the swingarm on a custom mount and the caliper mount with longer bolt. I did just that along with a swing arm brace welded in place.
http://www.superhawkforum.com/forums/mo ... unt-31513/
It worked for him, should work a treat for me...
Ahh no
The first failure was the OEM caliper mount fracturing.. you can see that in the thread above starting at post 120
http://www.superhawkforum.com/forums/mo ... post380045
new caliper mount was procured and fit, while I searched for a better solution on mounting a by design underslung caliper.
I changed the caliper position, and thus thrust angle by shortening the strut.... By all accounts that worked to lower the stress on the caliper mount however it moved the failure point to the strut material itself.
I made several mistakes..in material selection and design..I also underestimated the amount of force that the strut would need to hold back.
The fix is, all new rod ends as these have been subjected to forces I don't want to trust them to again. Reality is, even the smaller M6 one has a dynamic load limit of almost 20,000lb, and more in compression.. So the mount from the swing arm will fail long before these Chromoly rod ends fail.
Strut material has changed from 13mm dia 7075 al to 1/2mm (12.7mm) dia 4340 vacuum melt cold rolled steel bar.
Threads will be cut like last time, but there will be more material left after cutting threads even though the dia is smaller. Last time I was concerned with the Chromoly rod ends pulling threads from the aluminum bar.. so I used SS thread inserts....which worked,, the threads did not fail... that material failed just ahead of the threads because the cross section was too thin after the oversized thread insert installed.
The failure analysis I did on the first part failed to consider the final OD of the strut at threaded ends (GIGO, garbage in, garbage out) and failed to consider the micro fractures that happen when you cut the material with an edge.. like say a carbon cutter, or tap.. I remembered this from the days I learned about boring motor cylinders and the need to take progressively shallower cuts as you neared the final pre hone dimension...so the final microfractures (about 50% the depth of the cut) would be removed in the rigid honing process. Too bad I did not consider that same concen when I cut threads into the 7075 for the thread insert.
I actually have not found the data I want for cutting aluminum yet..is the microfractures not the same issue because of the elasticity of AL vs the iron bore of a cylinder. Or even if cutting steel like 4340 or other Chromoly steels exhibit the microfracturing I was taught happened with cutting iron cylinder bores.
In any case, I'm not leaving a weak link on the strut rod this time.. 1/2"(12.7mm) 4340 vacuum melt cold rolled steel bar, drilled and tapped m6 on one end, M8 on the other will have a higher load capacity then the shear strength of the fasteners holding it in place or the caliper mount, or even the welded on swing arm mount.
Flame suit on...... Poke fun all you want... we knowingly take risks when we depart from OEM R&D materials and designs . I accepted that risk and lost this time,,,,,, time to try again..
The idea came from a bloke on this very forum... rotate the brake caliper down using a stock caliper mount, and a strut mounted to the swingarm on a custom mount and the caliper mount with longer bolt. I did just that along with a swing arm brace welded in place.
http://www.superhawkforum.com/forums/mo ... unt-31513/
It worked for him, should work a treat for me...
Ahh no
The first failure was the OEM caliper mount fracturing.. you can see that in the thread above starting at post 120
http://www.superhawkforum.com/forums/mo ... post380045
new caliper mount was procured and fit, while I searched for a better solution on mounting a by design underslung caliper.
I changed the caliper position, and thus thrust angle by shortening the strut.... By all accounts that worked to lower the stress on the caliper mount however it moved the failure point to the strut material itself.
I made several mistakes..in material selection and design..I also underestimated the amount of force that the strut would need to hold back.
The fix is, all new rod ends as these have been subjected to forces I don't want to trust them to again. Reality is, even the smaller M6 one has a dynamic load limit of almost 20,000lb, and more in compression.. So the mount from the swing arm will fail long before these Chromoly rod ends fail.
Strut material has changed from 13mm dia 7075 al to 1/2mm (12.7mm) dia 4340 vacuum melt cold rolled steel bar.
Threads will be cut like last time, but there will be more material left after cutting threads even though the dia is smaller. Last time I was concerned with the Chromoly rod ends pulling threads from the aluminum bar.. so I used SS thread inserts....which worked,, the threads did not fail... that material failed just ahead of the threads because the cross section was too thin after the oversized thread insert installed.
The failure analysis I did on the first part failed to consider the final OD of the strut at threaded ends (GIGO, garbage in, garbage out) and failed to consider the micro fractures that happen when you cut the material with an edge.. like say a carbon cutter, or tap.. I remembered this from the days I learned about boring motor cylinders and the need to take progressively shallower cuts as you neared the final pre hone dimension...so the final microfractures (about 50% the depth of the cut) would be removed in the rigid honing process. Too bad I did not consider that same concen when I cut threads into the 7075 for the thread insert.
I actually have not found the data I want for cutting aluminum yet..is the microfractures not the same issue because of the elasticity of AL vs the iron bore of a cylinder. Or even if cutting steel like 4340 or other Chromoly steels exhibit the microfracturing I was taught happened with cutting iron cylinder bores.
In any case, I'm not leaving a weak link on the strut rod this time.. 1/2"(12.7mm) 4340 vacuum melt cold rolled steel bar, drilled and tapped m6 on one end, M8 on the other will have a higher load capacity then the shear strength of the fasteners holding it in place or the caliper mount, or even the welded on swing arm mount.
Flame suit on...... Poke fun all you want... we knowingly take risks when we depart from OEM R&D materials and designs . I accepted that risk and lost this time,,,,,, time to try again..
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Re: Under swing arm brake and what went wrong
at least your still around to analize what went wrong
Re: Under swing arm brake and what went wrong
Interesting analysis Erik and good of you to step up as a warning/explanation to the next to tread that route. Glad you're not too badly damaged fella.
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F3, 954 USD front, K Tech springs, Braced swinger, Penske shock, Six spoke Mockesini wheels, Harris rearsets, QaT, Flywheel diet!, A&L stacks, stick coils, K&N, FP Ti jets, lashings of Ti & CF
Re: Under swing arm brake and what went wrong
so glad i read that. i was thinking of doing the same because i have a blade brace to weld onto my swinger...... maybe time i had a retink
the older i get,the faster i was
Re: Under swing arm brake and what went wrong
i'm with fabio on this one E.Marquez
i watched your thread with the swinging arm and rear brake conversion and enjoyed it
but you have had a nasty fall
i understand why you do this sort of modding but whats the real gain of lowering the rear brake is it really going to make that big of a difference i would rather know that your going to be safe than doing test pilot again
good luck with what ever you chose
i watched your thread with the swinging arm and rear brake conversion and enjoyed it
but you have had a nasty fall
i understand why you do this sort of modding but whats the real gain of lowering the rear brake is it really going to make that big of a difference i would rather know that your going to be safe than doing test pilot again
good luck with what ever you chose
told you not to but oh no you knew better
Re: Under swing arm brake and what went wrong
Why? Why not?macdee wrote: i understand why you do this sort of modding but whats the real gain of lowering the rear brake is it really going to make that big of a difference i would rather know that your going to be safe than doing test pilot again
good luck with what ever you chose
Why do we make any changes at all to bikes as they come from the factory? To make them ours.
Other than that, I installed the swingarm brace in a way the standard fitting rear caliper is not possible.
Some choose to weaken the brace to fit the caliper in stock location.. I choose to not do that and move the caliper.
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Re: Under swing arm brake and what went wrong
You know you can use a fireblade caliper bracket to position the caliper in such a way to clear an modified brace?
Glad you are ok, good luck with it if you continue.
Glad you are ok, good luck with it if you continue.
Jamie
Re: Under swing arm brake and what went wrong
Thanks, yes i knew that, but not the way I went for my swing arm MODsJamoi wrote:You know you can use a fireblade caliper bracket to position the caliper in such a way to clear an modified brace?
Glad you are ok, good luck with it if you continue.
Mine is under the swing arm, as have been Many other bikes on the road.
I just have to over engineer the design so I don't see a part failure.
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Re: Under swing arm brake and what went wrong
what year of blade carrier do you need to relocate the storm caliper? is it a straight fit ?
the older i get,the faster i was
Re: Under swing arm brake and what went wrong
Hmm reading with interest.. Yes I'd also like to know what caliper carrier is fitted above.. And it must function in exactly the same way as oem as this thread seeks to conclude I think. Geordie
Re: Under swing arm brake and what went wrong
any news on the brackets needed for this?
the older i get,the faster i was
Re: Under swing arm brake and what went wrong
You need the slider on the fireblade swing arm cut off a donor... then cut off the SH one as well and weld on the fireblade slider.. then use the fireblade caliper mount.fabiostar wrote:any news on the brackets needed for this?
There is nothing wrong with doing that, but I wanted the caliper below so never bothered with figuring out what year was best for swap. Id bet they are all the same though.. so get your donor fireblade swingarm of any year that has the type of brace you want (single boxed front section or twin spar) and get a caliper bracket of the same year.
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Re: Under swing arm brake and what went wrong
This may help you visualise what is needed -fabiostar wrote:any news on the brackets needed for this?
http://vtr1000.org/phpBB3/viewtopic.php ... ce#p153524
Carpe diem, quam minimum credula postero
F3, 954 USD front, K Tech springs, Braced swinger, Penske shock, Six spoke Mockesini wheels, Harris rearsets, QaT, Flywheel diet!, A&L stacks, stick coils, K&N, FP Ti jets, lashings of Ti & CF
F3, 954 USD front, K Tech springs, Braced swinger, Penske shock, Six spoke Mockesini wheels, Harris rearsets, QaT, Flywheel diet!, A&L stacks, stick coils, K&N, FP Ti jets, lashings of Ti & CF
Re: Under swing arm brake and what went wrong
Sorry to hear of this. Must have been hair raising!
Can I ask a question, which applies generally to this type of rear brake anchoring, as opposed to the truly floating system, which feeds loads into the main frame.
Surely a fair proportion, if not majority of the brake torque is resisted (via the caliper bracket) by the wheel spindle bolt clamping everything together? Prior to modifying I assume the caliper bracket was located in position by a large tang, which locates in a slot fab'd into the swingarm? So how much of the function of this tang is towards simply positional purposes and how much towards helping out with true torque reaction?
Cheers.
Can I ask a question, which applies generally to this type of rear brake anchoring, as opposed to the truly floating system, which feeds loads into the main frame.
Surely a fair proportion, if not majority of the brake torque is resisted (via the caliper bracket) by the wheel spindle bolt clamping everything together? Prior to modifying I assume the caliper bracket was located in position by a large tang, which locates in a slot fab'd into the swingarm? So how much of the function of this tang is towards simply positional purposes and how much towards helping out with true torque reaction?
Cheers.
Re: Under swing arm brake and what went wrong
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.
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.
It's not falling off, it's an upgrade opportunity.