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I've never seen one of those before...a single sided four leading shoe. I'd like to get one of the big ass Laverda front drums...like 230mm or something, pretty light too I guess.
JohnnyB
 

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That's a heck of a price for a 230mm Grimeca. I think the typical price from a US dealer is usually $700+
I'm fancinated by the large brakes but the weight always turns me off...being a small bike racer. I sure would love to see how much I could shave off my lap times with an RS125 disk brake on my bike.
JohnnyB


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JB,
This guy has the Grimeca 230mm 4LS brakes on E-bay UK all the time. They usually go from $500 to $700 US. Plus another $100 or so to get it to the states.
Cheers, Bret @ Glass from the Past
 

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Discussion Starter #7
Bull,
While I can appreciate the time and effort involved to build a custom, that thing leaves me flacid. Like Rosko said, what a waste of a Norton. And juice brakes of any kind are kind of boring to me. Sure they work well and his rotor design is different, nbut there is nothing mechanical to look at. I get me kicks from seeing things move and operate. A cut away view of Desmo valve gear, or better yet, the valve gear of a Parilla 250 motor. A gear driven camshaft with a single lobe (yes, just one) operating the intake AND exhasut valves via 2 inch long push rods and rockers. It's like watching a Rube Goldberg machine with a purpose.
The brake in the auction, besides being a cool historic racing piece, has a unique operating style with the brake arms and cams working in mirror image of eachother. That is really cool to me.

JB,
If you didn't already know, some of the early 70s Ducati Desmo singles came with a Grimeca double sided single leading shoe front brake. If I had to guess I'd say it was 150-180mm. Google "Ducati Silver Shotgun" to see one. I believe it should mount up your Ducati 350 forks without any mods.

Cheers, Bret @ Glass from the Past
 

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well really Im the King of all that mechanica look, in my own mind !There is no question to me,this is a cool bike and it truely looks mechanical.In a limp sausage ...salvador dali look to it .and parimater brakes thats just a different mind set to come up with not only the idea but actually building it .Its Cool.......

Ihave always been a fan of massive mechanical shoe brakes for the look factor I think thats well known.

Im so far behind ,that I think Im in first.
 

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Bret,
I'm already prepping a 200mm T500 drum for the Ducati. I'm a big fan of the T500 for a light bike (350 or smaller). They are a tad fragile for anything larger. I have one on my 200gp bike...can do stoppies with it. I did build a bike a while back for a guy...another Honda that had the double sided single leading shoe...200mm I think...stopped better than I though it would considering the smallish surface area on the shoes. The double sided stuff seems to work better because it doesn't torque on the hub...nice balanced pressure on both sides. Also the center supported bearing tube seems a better setup.
JohnnyB
 

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"The brake in the auction, besides being a cool historic racing piece, has a unique operating style with the brake arms and cams working in mirror image of eachother. That is really cool to me."

Well put... I like the fact that its eligibal for vintage racing. I like my brakes I have now but it would cool to out brake Johnny with a cool piece of history.

Aaron
 

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Discussion Starter #12
"parimater brakes thats just a different mind set to come up with not only the idea but actually building it .Its Cool......."

Bull,
The guy in your link didn't come up with any new idea regarding the perimeter brakes. They've been around for at least 25 years.

Go here to see the real inovator.

http://www.osmoswheel.com/index.asp?lang=en

Cheers, Bret @ Glass from the Past

Edited by - bret on Mar 25 2007 4:24:23 PM
 

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I have some basic drum brake questions. JB already answered part of it with a double sided brake possibly not torqueing the hub because it is balanced both sides. What advantage would a 4 leading shoe single side offer over a 2 leading shoe single side if the pad area and the swept area are the same? If it is having twice as many leading edges than shouldn't a properly adjusted brake get the same amount of shoe on the braking surface and the edge shouldn't matter?
My other idea is, Couldn't a double sided 4 leading shoe brake be able to be fabricated by taking 2 Honda 350 drums and turning off one spoke flange and the closed side of the drum all the way to the braking surface, then fabricating a center bearing support and welding the whole mess together. That way you could use common components such as backing plates and shoes and only have to do a little work to a stock backing plate to fit it to the right side.
Is it feasable, especially compared to the cost and weight of other brakes?

Ken


AHRMA 412
Vintage racing - old guys on old bikes
 

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Ken,
It has to do with the way the shoes are levered against the drum. The arc of a brake shoe can't exactly match the arc of the drum or the pivot end of the shoe would always be slightly dragging the drum. The more points at which the circle made by the shoes can be expanded, the closer the arc of the shoe can be to the actual arc of the drum. It also has to do with the way a brake drum "auto actuates" Only the "leading shoe" auto actuates...(which is when the rotation of the drum tires to pull the shoe harder into the drum)..so the more leading shoes you have the more auto-actuation...kind of like a power brake.
Imagine this....you have a mandrel that expands into a hole to grip it, This mandrel only has two sections and must be small enough to fit into the hole....as it expands the peak of the two sections contacts the inside the hole yet the edges of the sections do not. Picture the same mandrel with four sections....now you have four contact points.....eight sections...eight contact points.
Maybe I'll do up some CAD drawings to demonstrate.

I've often thought of your four leading shoe conversion from standard drums...yes I think it's possible. It would require a level of aluminum welding skills I don't have. I would lean towards cutting a two hubs right down the middle...machine out the center....weld them together, machine up a new bearing tube/ center section...weld it in. Machine the shoes down narrow enough to fit each side. Still leaves the problem of the other backing plate being "opposite" rather than "mirror" which could complicate the linkage.

I've got a few nice 180mm CB160 brakes lying around....I'll play with them when I get the time to see if it feasible. Just mating two drums together probably wouldn't work due to the excessive width of the resulting hub. Would be an interesting project. And yes, the biggie would be readily available parts.
JohnnyB
 

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JohnnyB,
I understand about the self actuating part and I thought that with a double leading shoe you don't really have a pivot end of the shoe, that with 2 cams in the backing plate you are moving both ends of both shoes out at the same time.Isn't that why you radius brake shoes to match the drum? I have never truly set up a drum for racing with fancy shoes and such. I just make sure that the stock shoes are unglazed, adjusted properly and the wheel is centerd by pulling the brake on hard while tightening up the front axle bolts. Then I just squeeze like hell on the track. I would like better brakes. On a single leading shoe design I can see the issue with radiusing the shoes to match the drum being a ptoblem if the pivot end is fixed and on the trailing shoe the leading edge is the one that is pivoting. All in all not a great design.
As far as making 2 honda drums work together, my idea was about like yours except instead of cutting the drum in half I would cut it at the edge of the braking surface and weld it to a center plate that is flat and would carry the bearing tube. It would be wider than stock but I think with some trimming of the backing plate and such it would still fit with stanard fork spacing, just wouldn't need spacers. That way you wouldn't need to thin the shoes. I think with a stock honda backing plate that if you flipped the brake arms 180 degrees the only other issue would be the brake stay mounting boss would need to be cut off and moved 180 degrees to the other side of the plate. I wish I had a lathe and a mill and knew how to weld.

Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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Ken...a double leading shoe brake still has two pivots and two cams. Each cam works on one shoe...the reason they are special compared to a single leading shoe is that both shoes of a DLS brake will auto-actuate...whereas with as single leading shoe...that has only one cam..both shoes must pivot from the same side of the drum...making one shoe that doesn't auto-actuate.
A lot of people don't realize that without the auto-actuation a brake drum would not work at all...or just barely. Think about the force you apply at the lever, spread out over the several sqaure inches of shoe surface...not enough pressure to do anything...the auto-actuation is where the vast majority of the brake force comes from.

A double leading shoe has no advantage when it comes to contact points on the drum, a double sided (4LS) does a small bit just because you can usually fit in a larger contact area. A single sided four leading shoe does have a contact point advantange ( four instead of two). Also...as the shoe degrees of arc is decreased the auto-actuation force increases. Imagine a brake with a hundred tiny leading shoes...as soon as you touched the brake all those little shoes would try to wedge against the drum and lock up. It's hard to explain without getting into serious geometery...but as the angle of the shoe to the pivot becomes greater, the tendency of the shoe to wedge against the drum becomes greater....this angle increases with a decrease in the degrees of arc of the shoe....because the distance to contact the drum remains relatively constant, while the length of the lever (shoe) decreases. Lay down a 1 foot ruler and left the end 1"...the angle is minimal...lay down a 1" ruler and raise the end 1" and it's a 45 degree angle. In this example the 1" is the distance from the shoe to the drum....the ruler length is the length of the shoe along the drum.... as you can imagine, the shorter shoe, with the greater angle will tend to wedge against the drum more forcefully. The angle of the shoe directs the vector of the forces...the greater the angle the larger portion of the force is vectored into the surface of the drum.
How come a single sided 4LS brake doesn't lock up? Well as the arc degrees of the shoes decrease you can arc the shoes for a closer fit to the drum...which lessens the 1" in the ruler example...which decreases the angle of the shoe but creates more contact area...so you end up with the best of both worlds...smooth powerful auto-actuation...and more shoe to drum contact area.
JohnnyB
 

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JohnnyB,
Thanks for the explanation. Makes perfect sense now. I just never really thought about it before. Can you make me a brake with 100 little shoes? How about a double sided 8 leading shoe?

Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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Discussion Starter #20
OK, now I'm completely in love.....and this time I mean it.
Found this while flipping through Mick Walker's 'Cafe Racers of the 1960s'. Same manufacturer and style but TWICE the shoe count of the item in the auction....An 8 leading shoe. AAaaaahhhhhh......



Cheers, Bret @ Glass from the Past
 
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