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  #1  
Old 4th August 2021
panama86 panama86 is offline
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Question XLCH chopper rear hub/brake issues

G'day guys,
I'm currently building a 1970 XLCH, this is my first sporty, other bikes are a 51 FL and 78 FX.

I'm almost finished with the fab work on the bike and getting ready to pull it down for paint. This bike came to me with what I presume to be the stock frame which had been hardtailed using a weld on hardtail kit, not sure the manufacturer. The frame has quite good lines, somehow managed to avoid the dog leg most rigid sporties have.

Anyway, down to the issues.

Brake pivot & anchor bolt
This frame has the usual slot like the stock swingarm had for the brake anchor to sit in but then the outside edge of the slot on this frame is narrower than the stock swingarm slot. There is a step. For this reason, the pivot stud that runs through the top hat spacer and into the thread in the brake shoe pivot cannot be tightened down as it reaches a point where it cannot rotate in the slot without the flats of the bolt hitting. The width of 2 flats on the bolt is the same size as the narrow section in the frame slot. I am unsure what the set up should be here. I know some of these bikes had the top hat spacer free to move back and forth in the slot if chain needed to be adjusted for example and some were actually bolted down tight to the frame. my understanding is that this bolt style was meant to tighten down tight to the frame holding everything tight. My question is, would just a washer or a machined spacer for the outside of the frame work for me to tighten everything down or should this setup be free to move back and forth freely if that makes sense.

The other issue I'm facing here is with the stock top hat spacer in place between the backing plate and the slot, it would cause the backing plate to sit unevenly in the drum leaving an uneven gap between the plate and the drum at the opposing end of the drum to the brake pivot. This led me to conclude that the spacer needed to have it's flange thickness machined down a little to even out the plate. Any idea what else could be causing this?

Some photos to show the issues i'm talking about.



Cheers
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  #2  
Old 4th August 2021
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Mine is older stuff but I think you need the double flatted flange/washer as the slide in the slot piece that also allows the alignment screw to tighten up when you have the brake shoes up against the ID of the drum.


I converted mine to disc but you can see my frame slot is wider than yours.
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  #3  
Old 5th August 2021
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This is a common problem on aftermarket stuff.
Also the year model application may come into play as I think different methods were used over the years.
The last one I did I wound up reworking the backing plate and the pivot anchor to work with the Paughco frame, I also had to bush the actuator hole so it didn't wobble.
A disc brake would be so much easier, but to maintain period correctness.......

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Old 5th August 2021
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Waitaminit!



An OEM backing plate does not have welds around the spuds!
What is that?
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Old 5th August 2021
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I bought that in ‘80. I believe from Drag Specialties. It’s a chromed all steel rear backing plate for Ks and XLs. Also the chromed steel drum and sprocket.

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Old 6th August 2021
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Ok so I have a small update on this issue.

The drum and backing plate combo i had on in the photos above came with the bike. They look like the they would have been original on the 1970. The drum was in pretty poor shape though. I had a new v-twin drum and a later model backing plate on the shelf, the type that has 2 holes towards the back of the plate the same as this:


When i fit up this new drum and backing plate and tighten the axle down but leave the brake anchor bolt off everything sits straight. I've added the thick washer under the bolt that was missing in the above photo and as soon as i tighten the anchor bolt down to the frame the backing plate twists towards the front and top of the drum. Leaving an uneven gap around the edge and this twist will likely cause the plate to crack eventually. It's obviously doing this because I am marrying the backing plate to the frame by tightening it down and potentially the frame is a little twisted or something.

My question now is, does the style of anchor hardware poster above by ryder_rick actually anchor down to the frame or does it merely locate itself in the slot in the frame? If that's the case, it could solve my problems as the tightening to the frame is what seems to be pulling things out of alignment. Also, with that style of anchor, could you tighten down the alignment screw and nut before installing the plate in the frame? Or does it need to bolted down from the outside once everything is together? Hope that makes sense.
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Old 7th August 2021
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panama your brake anchor system is 73-78but your frame is made for 52-72 system. you need to get that system. check part book an post back with any questions.

the backing plate tim shows is an old trock steel unit. rigid guys who fliped the brake arm upside down on the camshaft would routinely shatter the oem alum unit. hence the trock steel.

back to the early anchor: it doesnt tighten to the frame. it just titens to the backing plate and rides in the frame (or swingarm if not rigid).
this allows chain to be adjusted without disturbing the anchor.

how the brake actually works:
the cam presses the shoes to the drum.
the cam is held in a set position by the backing plate. ie: the fit of the cam shaft to the backing plate bore cant be sloppy (or your brake feedback is terrible).
but
the shoes need to "find their best contact to drum" regardless of where the cam resides.

so
a close look at all the parts on the anchor side will show how this is accomplished.
where the anchor stud passes thru the backing plate the fit is very sloppy.

imagine you have the wheel on the bike as normal but just the anchor was left loose.
when you apply the brake the cam forces the shoes in contact with the drum.
the shoes will shift in relation to the cam as they marry up to the drum.

when shoes marry up to the drum they bring the anchor stud along for the ride. the backing plate hole the anchor stud passes thru need to be large enuff to allow the the shoes to find 'home'

now is when the early anchor gets tightened-- while the brake is applied.
its also when the late anchor gets titened-- while the brake is applied.

the difference is the early set up is "free floating" in relationship to slot on the frame.
its entirely connected to the backing plate. it just pushes on the frame, its not bolted to it.
that means chain adjustments dont require you to mess with the anchor at all.
where as the late setup forces the backing plate against the frame and the shoe contact to drum is disturbed while doing so.
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Old 8th August 2021
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Cheers for that super informative response Dr Dick.

Makes sense what you said about the style of anchor I have. I've ordered the earlier style anchor so will report back once I receive it and check how it fits up. I think will solve the issue of my backing plate skewing when tightened to the frame too.

You mentioned backing plates shattering when the chopper guys were running the lever flipped. Funny you should mention that because it's happened to a few friends of mine with that set up. I also have it set up that way on this bike. What is it about flipping the lever that causes them to shatter? I recut my brake cam so I could have a smooth transition when braking. Only difference I can think of is the direction the cam rotates when breaking, clockwise when the lever is in the stock position and counter clockwise when it's flipped. Can't wrap my head around why that causes them to shatter. I also had a look around online for a steel unit but couldn't find anyone still selling them.
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Old 8th August 2021
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seem like you are heading in the right direction. those issues could be solved with a little machine work making some parts.
i will throw this slinky out and see if it returns: there is a leading shoe and a trailing shoe. there is also some ramps on the cam. if you reverse the direction, there is increased force applied to the cam in the wrong direction.
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Old 8th August 2021
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on right side of bike looking at the backing plate.


when brake gets applied the backing plate wants to rotate clockwise.
the anchor stop the rotation.


inside the drum the top shoe thrusts against the anchor stud this is the leading shoe.
but the bottom shoe(trailing shoe) thrusts against the cam which transfers the force to the camshaft then to the plate which transfers it to the anchor stud.


the leading shoe gets "wedged" into drum by wheel rotation but the trailing is trying to skid off the drum.


if you get the plate and shoe assm on workbench and rotate the arm in the oem direction you will see the the lower trailing shoe moves more than the upper. a close look will how this happens will become apparent.
that means the trailing shoe get more expanding force than the leading. but the lower has skid action not wedge action.
this applies a good amount of rotational force into the cam which is feed back to you as pedal feel. and it limit the wedge action of the leading shoe because the leading shoe doesnt move as far.


when you flip the arm to the bottom you reverse the relative movement of the two shoes. the leading now becomes dominant shoe. and pedal feel disappears. because the feed back to the cam becomes almost nonexistent.
but the force now all goes to the upper, any balance of forces between top and bottom is destroyed.
the brake is now grabby.



that said
remember the plate is trying to rotate clockwise normally.
if the anchor pad slot in the hardtail is oversize it allows the plate to rotate the wrong way if the brake is applied in reverse, like when bike is rolling backwards on a hill.


additionally when arm is on bottom steppin on brake pedal also creates this backward motion of the plate.


so if the plate has rotated in the wrong direction AND you stab the brake the plate rotates forward and that forward rotation stops suddenly. all the force is now from just the upper shoe into the anchor.
sand cast backing plates arent flexible enuff to deal with the unbalanced forces.

steel is.


as a sportster rigid frame expert i never flip the arm. and i always use the sand cast backing plates.
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