Dr. Shop Teacher's Tonic le Moto--Broncco T-XL

#62
Fender Bracket and Notching:
A couple days ago I re-bent the rear fender bracket and notched the fender. I had looked at pictures and the OG fenders were actually flattened at the chain location. I was concerned that chain slap would tear the powder up on the fender, so I just went on and notched it a bit oversize.
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Caliper Bracket (Round One):
The location of the tabs for DB30 calipers make building bracket pretty challenging. Because the caliper fits reverse of it's intended location, a lot of time was spent determining the proper orientation. To get it (partway) right, I started with a plywood pattern. Here's the caliper located to find the right orientation (it's in about the same place as the massive original caliper).
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I used my machine drawing of the sprocket locate the axle center and laid out the caliper centerline to be on the same plane as the axle. the hard part was figuring the exact location of the caliper (pad surface) on the sprocket to spin freely). The plywood mock-up seemed to work fine.
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Then transfer to metal. Here's where the fun began as nothing was easy. Note how I set the slot for locking the bracket in position. I used 1/8" steel plate for the bracket given the space limitations. Cutting and shaping was an ordeal....The second photo shows it in place but....
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#63
Caliper Bracket (Round Two):
So most of Saturday was making the bracket and all of Sunday was spent re-making the bracket as I just wasn't happy.
I changed up the design somewhat to make it easier to cut. The centerline of caliper is still on the same plane as the axle. Rather than using a hole saw to open up the caliper location, I drilled several 1/2" and 3/8" holes.
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All of this was hand filed to bring it to shape. I did use the angle grinder for the out facing surfaces.
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I worked from the caliper mounting bolts to the axle to make sure my measurements stayed consistent.
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Here's the template, bracket one and the revised bracket two: IMG_0287.jpg
I removed the cable stop from the caliper and this will be located on the swing arm.
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I also had to reshape the inside of the caliper, as it has a outside curve which interfered with full pad contact on the sprocket. This was a lot of trial and error.
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Here it is assembled.
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And mounted in place. Plenty of room for the cable and lever travel. I'll be welding nuts on the bracket to allow for y-axis adjustment of the caliper.
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Attachments

#73
It's a matter of mechanical advantage/leverage. The closer the caliper is to the axle, the less effective it will be. That's one reason why high performance cars and motorcycles have large diameter rotors. The closer the caliper is to the axle, the more force/pressure the caliper must apply, increasing pad to rotor friction, for a given braking performance result. The increased pressure and friction will produce more heat and wear, obviously. I'm somewhat doubtful that the mechanical caliper would be capable of applying sufficient pressure to overcome the mechanical disadvantage. I guess you'll find out. ;) Very nice fab work, as always, Doc.
 
#74
It's a matter of mechanical advantage/leverage. The closer the caliper is to the axle, the less effective it will be. That's one reason why high performance cars and motorcycles have large diameter rotors. The closer the caliper is to the axle, the more force/pressure the caliper must apply, increasing pad to rotor friction, for a given braking performance result. The increased pressure and friction will produce more heat and wear, obviously. I'm somewhat doubtful that the mechanical caliper would be capable of applying sufficient pressure to overcome the mechanical disadvantage. I guess you'll find out. ;) Very nice fab work, as always, Doc.
Unfortunately, the only other option is a clutch brake...which I can add if need be. The OG design had the caliper as I have it but obviously with a much older (and less efficient) caliper design. Ideally, I would have designed a hub for the opposite side of the wheel and done a disc/caliper on that side. However, the wheel design precludes that--though a three piece hub could have been made if I wanted to spend a small fortune with machine shop services. Hydraulic would have been preferred....but no way to modify the DB caliper to work.
 
#75
Unfortunately, the only other option is a clutch brake...which I can add if need be. The OG design had the caliper as I have it but obviously with a much older (and less efficient) caliper design. Ideally, I would have designed a hub for the opposite side of the wheel and done a disc/caliper on that side. However, the wheel design precludes that--though a three piece hub could have been made if I wanted to spend a small fortune with machine shop services. Hydraulic would have been preferred....but no way to modify the DB caliper to work.
The brakes look great Pete. I admire your mad skills.
 
#77
Bucks and Parts:
I made two bucks for the bike--one for the fuel tank shroud and one for the clutch/chain guard. The fuel tank shroud has multiple compound angles along its length, so it took a while to make.

The shroud buck is four pieces of wood sandwiched together and shaped to fit the inside curve of the frame tubes. It'll stay as a parallelogram as fully mimicking the OG tank isn't really possible.
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I covered it with cardboard to make the pattern to cut the sides and top out of aluminum. You will note the seat by @manchester1. Like wow!
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The clutch guard buck was done similarly, but much easier to do.
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I laid out lines with a scratch awl, masked it and cut with a sabre saw (18tpi and slow speed).
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The edge was clamped to the buck and slowly heated so I could make the curve with a wooden block.
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Lastly, I headed back to the welder for some touch up work and had the pins welded in for the cam chain tensioners. I used 1/4" scrap rod.
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Once I get the shroud pieces cut, John, my welder will sew both pieces together.
 
#79
Fuel tank shroud:
Cut the pieces for the shroud yesterday and today...a little bit of finish work still needed, but it's shaped. I started with the sides, as I was running short on aluminum and knew I could piece the smaller sections.
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Then I clamped each piece to the buck and heated the aluminum to fit the form (yes, the wood charred). I used an oak block and a ball peen to fit the curve.
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Then I cut the smaller pieces to fill in the shroud. If I had enough aluminum remaining, I guess I could have made an actual tank out of the shroud.
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A 2-quart kart tank fits inside nicely.
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Another shot. When clamped it looks pretty good.
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