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Pictures of Drilled/Lightened RD Brake Shoe Plate

Started by sav0r, December 27, 2020, 03:47:22 PM

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sav0r

I wasn't sure of the technical name, so I called it the "brake shoe plate." I am referring to the external plate that supports the brake shoes on the rear drum of an RD.

I know many have added various weakening holes to remove some weight on these parts, especially so the shoe plate. I finally have a spare plate to do some work on and plan to come up with a nice program to do this work on the mill. I'd like it to have a classic look while also removing as much mass as possible. I'll probably try to do some rudimentary failure mode analysis to make sure I'm not getting too crazy.

I am not a huge fan of the Swiss cheese random hole look many achieve, but done well I think it can work. I have seen some drums with reasonable size holes and stainless mesh riveted in (certainly on English bikes). I much prefer that look and I think it will achieve the best performance, but with the webbing on the back of the plate there was to be some consideration to where material can be removed and how much can be taken.

So, if anybody has some sweet photos I'd love to see them.
www.chrislivengood.net - for my projects and musings.

oxford

#1
Not exactly what you are looking for but here's what I did.  (6) 5/8" holes drilled in it and the outer hub drilled between the spoke holes.

I went back and forth on what to do with the brake plate as I don't like the random holes/slots Swiss cheese look and without cutting into the reinforcement ribs you don't have a lot of good options. 

I would like to see some pics of what others have done as well.


sav0r

Thanks, Ox. Very tidy setup there.

It looks like we are the only two with interest. I guess I'll just do what I want. I'll try to post results as I get them.
www.chrislivengood.net - for my projects and musings.

teazer

I went with cable activation using a Suzuki GT750 cable on this TD3 with some RD parts.


Dvsrd

A FEM (Finite Element Method) analysis would be the way to do this properly.
However, if reduced unsprung weight is the main objective, a smaller diameter drum brake rear hub for cable actuation may be the best choice. After all, very few ride 2 up on an RD these days. And the stock rear brake is overkill for solo road riding .

sav0r

I suppose you are right. I was planning to remove material until I broke the thing, then would back off for the final design, and machine my second unit to that spec. There is a lot of webbing that supports material that doesn't doing anything, so I was going to lop the majority of it off. I'm not sure I really want to model it and run simulations.
www.chrislivengood.net - for my projects and musings.

suey1958

Savor, Glad you started this thread. I have seen the drilled brake plates on various bikes but never noticed a modified one on an RD.
Looking forward to see what you come up with.  :clap:

stresa

Made by a friend of mine a couple of years ago for me. Intention was to improve the looks and the cable brake line conversion, not to save weight.


Regards Uwe
81 Jackson Special 250, 2x 74 Yamaha RD250 racer + 1 street racer, 78 Yamaha RD400, 72 R5/RD350, 74 RD250 dirttracker street, 75 Yapol TZ250, 89 Honda RS125,
80 Hejira TM250, RD375/3, 77 Höpfner-TD3, 76 RD/TD3,
74 Yamaha TZ/RD250A, 78 Siroko TZ250, 75 Bakker TZ350B, Tomic 200, Waddon Rotax125

m in sc

#8
to be honest, there isn't anything really much to gain but cutting the rear brake plate, weight wise. one of the main reasons its there it is to keep debris out. like, pebbles etc, water, and so on. the edge of it is more like a lab seal specifically for this reason.   Ive seen some ridiculously cut down ones that worked just fine. Not my cup of tea.

however, on the lightweight, i did drill around the perimeter. primarily to allow brake dust to vent out which to me is the most important function, and possibly help cool, but it never gets worked hard.  (see pic).

Unless you were going to make a skeleton one, there no need to do an analysis for strength (unless maybe it was a front one). you can cut most of the flat material out from in between the ribs and it would be just fine.( But look like shit, IMHO.)
Look at how thin and flimsy a car drum brake backing plate is and you'd realize pretty quick an RD rear brake one is far stronger than it needs to be.

the lightweight RD rear brake. probably the most boring drilled rear plate ever.  The arm is a stock one I modified.

BTW, Uwe, that looks fantastic.

sav0r

My thinking was to remove basically most of the webbing, and probably open a few holes in the side for some fresh air. Then machine some flats to rivet some stainless mesh in. I didn't have any plans of any ram air, naca ducts, or things like that. At the rear wheel the aerodynamics are likely too complex to count on these items working without some sort of practical analysis. Also, as mentioned, the rear brake isn't particularly stressed especially not in street use. So the idea would be to reduce the material down to where it's as light as possible but still looks decent and classic. Being a brake obviously there needs to be a reasonable safety factor, so a little bit of analysis doesn't seem unreasonable.
www.chrislivengood.net - for my projects and musings.

sav0r

I put the brake plate on the mill and created a point cloud using my touch probe. Then I imported that into CAD. I used the point cloud to form a rudimentary model that I will clean up.

I also bought a lathe yesterday. I should have it in the shop in the next few weeks, it's a manual lathe that I will run manually for a while, then convert to CNC. So the plan right now is to use the lathe to reduce the webbing, then transfer to the mill to cut the openings. Seems pretty straightforward. I'm sure I'll have it all worked out in the next year or two...
www.chrislivengood.net - for my projects and musings.