MX Front Drum Brakes

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3/31/2016 3:33 AM

Hi Guy,s i like to get your ideas on Front drum brake performance, tip's and idea's,

I am talking very early eighty's single leading shoe, i wish for easier pull and more bite / power.

Are there better shoes to purchase, different compounds.
Are open bike wheel / brake combo's more powerful than, say a 125's,
Do different cables make a difference, OEM vs aftermarket

Any other tricks or tips

No double leading shoe suggestions please, not class legal.

Thanks Mark

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3/31/2016 4:46 AM
Edited Date/Time: 3/31/2016 4:47 AM

My normal setup is the following and usually very powerful. Not endo powerful but still very strong.

Rough up the drum with a porting sanding tool on a cordless drill.
Using sand paper taped to the drum arc a set of EBC G compound to insure full bite.
Lightly rough up the brake pad either with sand paper or I lightly sand blast them
I look for Teflon lined brake cables to ensure I get the most power from the brake lever to the drum
If need be find the longest brake drum lever but I've found that most of the late 70s are pretty long.
Install everything and do some hard embedding stops to adjust the cable/arm for max throw on the lever

If that doesn't work you can try a newer roller bearing clutch perch turned upside down to get even more power.

Good luck

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3/31/2016 9:08 AM
Edited Date/Time: 3/31/2016 9:09 AM

450's tips are really good, but the best thing to do is to true the drum (on a built wheel) and the shoes as they are installed on the backing plate. Race Tech will do this for stupid money, or you can build your own tool or have one built.

After that, a longer brake arm for more lavage, a new cable (I like OEM for some brands, aftermarket for others) and careful assembly so the shoes hit the drum squarely for the most contact.

Photo

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3/31/2016 10:46 AM

One of the most important things is to centre the drum in the hub so the shoes contact equally, and together.

The simple way to do this is to loosen off the axle clamp bolts and the axle a little. Spin the wheel (in the same diection as it would be if you were riding) and then grab a handfull of front brake and hold it on. If your on your own use a zip tie to keep the front brake applied. If you have a small child, wife, girlfriend, mistress, cleaner, dad or general dogs-body on hand, they can keep the brake applied for you. Tighten the axle, then the pinch bolts. Realese the brake and adjust. The drum should now be centred in the hub.

Stevie

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3/31/2016 4:18 PM

Stevie, a good friend, is 100% correct, if the brake shoes and drum are true and round. Otherwise you will never get the most out of your drum brakes. It is like using two fingers to grip vs four.
He should have know.

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3/31/2016 5:36 PM

Harry Klemm at Klemm Vintage has been running Kawasaki 350 Bighorn singles successfully as vintage roadracers, and a rule change meant he could no longer use period-correct DLS brakes like the 500 triple had, so he had to get the stock SLS brakes squared away, using methods described above. In the process, he discovered that the two wheel bearing seats in the hub were two separately done bores in the hub, not a single continuous bore; I think he found they were .008" out of line with each other, so the drum could not be truly concentric with the shoes. He addressed it with a new bore on each side for new bearings, and this optimized stock SLS front brake turned out as strong as the DLS he'd been using, and more raceable because it was less grabby than the DLS.

As Klemm points out, it wasn't a computer machining those hubs back then, it was Aki or Ake or Heinz or Jaroslav, and it might have been Monday when yours was made, so it's worth checking whether the drum is truly concentric with the axle. If you have a stock SLS that has never really satisfied you, it seems worth the trouble to investigate. I would never have thought of it, and even Klemm is candidly a little embarrassed that he spotted the problem by chance rather than realizing abstractly that he should check it if he was optimizing a wheel. He describes it much better than I have if you scroll down the Bighorn page to the chassis part at Klemm Vintage Bighorn setup

That is a very informative site IMO: Klemm does things his way, but don't forget he was the guy who built the CZ that Rex Staten holeshot the world on twice at the 1975 Carlsbad GP, and probably would have won if the CZ factory had not forced Staten to use stock forks, etc.

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4/1/2016 4:21 AM

It's hard to add anything to what's been said. You guys have given this a lot of thought.

The only thing I'd add is that I used to move my brake perch in towards the center of the bars as far as I could and still keep a comfortable distance for reach. Even an extra 1/2 " will give more leverage. Someone already said this, but I also used to add a 1/2 "or so to the brake arm at the drum. Add as much as you can without throwing the cable housing holder too far out of alignment. I'd want the cable to still have a pretty straight pull.

RB

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4/1/2016 5:30 AM

To add to RB and the comments on using a longer brake arm, please note that when you do use a longer arm, it is usually, but not always needed, to move your brake clamp/guide out from it present position so as to keep the cable at a straight a run as possible to the brake arm. You do not want to add a curve to the cable. This will offset the extension you just added as now you have to overcome the new bend in the cable.

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4/1/2016 6:44 AM

All great tips.
One thing I'll add is to check the contact patch of the shoes against the drum.
ride the bike, grab a handful of front brake and then investigate what the shoes look like.
I'll take a course file and rub down the contact areas(high spots) to even out the shoes, then ride and test again.
the object is to make sure the shoe has full contact against the drum surface.

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Larry Navarro - Spring,TX. Damm glad to meetcha!

4/2/2016 3:58 AM

Thanks Guy's, a wealth of information here to follow through with.

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4/3/2016 2:48 PM
Edited Date/Time: 4/3/2016 2:52 PM

Be careful choosing your brake shoes, see oem vs aftermarket photo shows CR250 stock and EB? Stock has probably 20% more surface area in length and width
As Stevie said center them up u can test and look for high spots, if not equipped with tooling.
Goog luck

Photo

Photo

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4/3/2016 3:02 PM

Major fan of Yamaha OEM shoes.

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Larry Navarro - Spring,TX. Damm glad to meetcha!

4/3/2016 10:19 PM

One point that does not seem to have been mentioned is that the brake cable has the most leverage on the actuating arm (and thus the shoes) when it is making a right angle to the actuating arm. The designers usually took advantage of this by having the cable start at an acute angle and swing out toward the right angle as the brake lever was pulled farther. It's worth looking into what is going on with this if you are optimizing a SLS brake. Too much leverage too soon could make the brake grabby, but too acute an angle throughout will not generate as much leverage at max grip. With an actuating arm on a splined shaft, for all you know someone may have reinstalled the actuator a spline wrong. So that is another consideration along with how straight the cable run is, as RBrider and RF145 point out. You may not actually need a longer actuating arm, just a straighter cable run and more perpendicular pull on the actuating arm. Or do all three.

I recall what I think was originally the 1972 Yamaha 250 conical hub as the 1970s standard for light weight and stopping power when people were changing front hubs for better braking on Maicos, etc. But my impression is that all the Japanese brands and Husqvarna had strong & light SLS fronts at the end of the 70s, KTM or Maico being less consistent/needing more setup, and Can Am prone to fading. Sometimes larger brakes on larger displacements. Choosing a non-stock front might come down more to ease of adapting and availability of good shoes as pointed out above, and you might want to make sure you'd really optimized the stock brake before you gave up on it.

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1/4/2021 1:37 PM

another easy and free thing to do is move the brake lever over as much as the bar bend will allow so you are grabbing the lever as close to the end as possible. Free leverage.

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Bret Bonham

1/4/2021 2:40 PM

I am working on a set of brakes with more brake material that has a high friction coefficient. I used an old set of shoes and glued/clamped/baked the material to the shoes. Then I cobbled together a fixture to arc the shoes to match the drum. This is my second attempt. The first attempt was unsuccessful because I chose the wrong brake lining material. These should work better. I calculated that I have approximately 3 square inches more braking material contacting the drum. Here are some photos:

Photo
Photo
Photo
Photo

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Bret Bonham

1/4/2021 2:44 PM
Edited Date/Time: 1/4/2021 2:44 PM

Here are the finished brakes. EBC on the left. Mine on the right.

Photo

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Bret Bonham

1/6/2021 5:55 AM

Not related to Brets post above, if anyone is using EBC shoes you'll always have a shitty brake no matter what you do.

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1/6/2021 6:03 AM

Bret wrote:

Here are the finished brakes. EBC on the left. Mine on the right.

Photo

It makes sense that having more material like you made on yours can only help. It's strange that every brake shoe is made with its material not fully wrapping around.
What bike did you make those shoes for?

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1/6/2021 7:40 AM

MaxPower wrote:

It makes sense that having more material like you made on yours can only help. It's strange that every brake shoe is made with ...more

1981 Maico 490 front brakes.

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Bret Bonham

1/7/2021 8:08 AM

Wondering about the physics of it: isn't the leading shoe actually pulled into the drum surface by the drum's rotation, creating more braking force? Much more force than our hands alone can supply--that is why DLS front brakes let you roll backwards down a hill & can be a real drawback on trails.

Does a shorter brake lining give the drum's rotation better leverage on the leading shoe? Perhaps enough to offset the loss of lining area? Or is it the opposite--does it reduce "drum rotation effect" to keep the leading shoe from being too grabby?

I am fuzzy on the physics of it.

Got my first pair of EBC shoes for a project for which I also have NOS Yamaha shoes. The EBC seem rather precisely sized to the drum: with the actuator on the stock spline position, you have to crank the adjuster 20 mm before you even get contact, but this has the cable & actuator pulling just to the desired 90° angle for max leverage.

The Yamaha shoe linings are much thicker, and the cable & actuator still at a relatively acute angle when contact begins. It's like the stock shoes are meant to get stronger as they wear, but the EBC are going to start at their strongest and lose effectiveness as they wear--make a good initial impression & then require replacement sooner. . . .

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1/7/2021 11:33 AM

speedman wrote:

Wondering about the physics of it: isn't the leading shoe actually pulled into the drum surface by the drum's rotation, ...more

Yes that is how a leading shoe drum brake works. The force vector generated by the friction pulls the shoe into the drum for a harder bit.

That said shoe contact patch actually is less relevant in braking force and is more relevant to heat dissipation, dust/dirt removal. Friction materials plays the largest role in braking performance and fade resistance.

Honda always had small drums and pads when you compared them to Yamaha and even Suzuki but they worked just as well.

Those of us with Can Ams have to go the relining route as there aren't any off the shelf shoes for the Girling brake drums of the 70s. sad

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1/7/2021 1:09 PM

speedman wrote:

Wondering about the physics of it: isn't the leading shoe actually pulled into the drum surface by the drum's rotation, ...more

Interesting, i had to look in my old books..
When the leading shoe have shorter brake linning, it is to reduce "drum rotation effekt", dont know the words in english, maby "servo effekt" or "Self-reinforcing"?
I have problem with my DLS brake on my CR480 -83, the SLS on my CR250 -79 have better braking power.. Have to look closer on the construction of the shoes (ebs)

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1/7/2021 3:18 PM

TTperra wrote:

Interesting, i had to look in my old books..
When the leading shoe have shorter brake linning, it is to reduce "drum rotation ...more

Poor performing dual leading shoe brakes are typically due to setup. Both shoes must contact at the same time They can be tricky and time consuming to adjust but once you get them dialed in they are fantastic.

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Bret Bonham

1/8/2021 6:19 AM

speedman wrote:

Wondering about the physics of it: isn't the leading shoe actually pulled into the drum surface by the drum's rotation, ...more

As I am collector of older stuff, 1960-1980, including magazines. I read in one of the not dirt publications on the Yamaha brakes. The actuator/cam was exactly that. It was a cam and the larger or thicker side went to the shoe that was pushed away. this allowed for even pressure across both shoes. They discovered this when they took the brake panel apart and got it in backwards. Went from a excellent to less than acceptable stopping bike. I do not think most brake cabs are built that way. Would be an interesting test.

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1/18/2021 8:08 AM

Bret wrote:

Here are the finished brakes. EBC on the left. Mine on the right.

Photo

Well, tried the brakes out. The stopping power was increased significantly. The only bummer is that the glue heated up and then everything failed. I either used the wrong glue or did not cure it properly. Since this material worked so much better I am likely going to try again.
Photo

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Bret Bonham

1/19/2021 7:35 AM

speedman wrote:

Wondering about the physics of it: isn't the leading shoe actually pulled into the drum surface by the drum's rotation, ...more

Hasletjoe wrote:

As I am collector of older stuff, 1960-1980, including magazines. I read in one of the not dirt publications on the Yamaha ...more

My dad had a 75 MX250 and the local Yamaha dealer said the YZ cam would increase braking. Turns out it was offset and it did indeed increase stopping power over the MX cam.

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1/19/2021 9:24 AM

I would get a two part epoxy from Lowe’s or Home Depot. I put a new roof on my old that had to be verified to withstand 170 mph hurricane. I had to embed 1/2 “ all thread every 2 ft 8” deep in the top of the wall to bolt the new top plate down. That epoxy will do the job for you .

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1/20/2021 2:01 AM

Worth trying once and worth trying again, @Bret--if the self-energizing effect causes grabbiness, it still ought to be the rider's personal standard for what constitutes "grabby," not a one-size-fits-all decision by the manufacturer. A big, skilled rider going fast has more kinetic energy to deal with than a small novice going slow, and a way more precise discrimination in dealing with that kinetic energy, so the skilled rider can be trusted with a more powerful brake that ramps up more quickly. Keep on gluing--

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1/20/2021 8:38 AM

speedman wrote:

Worth trying once and worth trying again, @Bret--if the self-energizing effect causes grabbiness, it still ought to be the ...more

I found a high temp version of the adhesive I used the first two times. I will be using rivets this time too.

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Bret Bonham