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Author Topic: rear drum brake being a bit odd  (Read 396 times)

Arizoni

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Re: rear drum brake being a bit odd
« Reply #15 on: April 27, 2014, 01:39:52 AM »
lemming:
Sectorsteves motorcycle is the only one I've ever heard of bending the swing arm.  I'm still trying to figure out how that could possibly happen by just using the rear brake.  There isn't that much torque on the rear brake even if the rear wheel is locked up.

If the rear brake shoes are adjusted correctly, the coil spring on the rear brake lever will automatically disengage the rear brake as soon as the riders foot releases the pressure on the brake pedal.
Don't worry about it but remember, the front brake on your motorcycle does over 80 percent of the braking.
Several racers I know only use the rear brake to keep the rear of the bike from coming around under heavy braking.  (I'm talking about 120 mph down to 20 mph for a sharp turn).
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary

suitcasejefferson

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Re: rear drum brake being a bit odd
« Reply #16 on: April 27, 2014, 01:40:06 AM »
First of all, a bike can be ridden fairly safely without a rear brake. I put over 20,000 miles on a Honda Rebel 250 with no rear brake. It was not intentional. I had fabricated parts to move the footpegs and shifter 6" forward, to give me more room, as the bike was considerably too small for me. I had started to fabricate a new rear brake pedal and linkage, but never finished it, because I had no trouble riding without the rear brake. The Rebel is not a sport bike. In a faster than normal stop, almost all of the braking is done by the front brake, and because of the forward weight transfer, there is almost no weight on the rear wheel. Just touching the brake can lock it up.

However, if the rear brake releases as soon as you release the pedal, it should not be unsafe. If the brake locks up, and won't release, you're in trouble. Same thing if the brake does not operate in a linear fashion, if it goes from barely braking at all to sudden lockup with no or very little extra pressure on the pedal. The front brake on my Kawasaki Vulcan 750 had this problem. It was virtually impossible to control under hard braking, it locked up every time, without warning. It was a dual disc setup, and I solved the problem by removing the entire brake from the right side, leaving it with one disc. It then performed perfectly. It could be locked up, but actually took some effort to do it. Normal braking was uneffected. I have put almost 60,000 miles on the bike after that modification with no issues.

I am not a motorcycle mechanic, but I worked 36 years as an auto mechanic. The brakes are very similar. I believe Steve's problem is caused by the brake assembly itself. I don't see how the swingarm or suspension could have anything to do with it. It almost has to be something to do with the way the shoes are contacting the drum. The harder the shoes contact the drum, the more friction is created, up until the shoes and drum are locked together. Any rear brake can be locked up, but you should have to push pretty hard on the pedal to do it. I sure wish I could get a look at the actual parts. I realize the bike was in an accident, but any accident damage to the brake should be obvious. Not being that familiar with RE (yet) I wonder if all the parts are the right ones, and if there is any binding anywhere, including the pedal and linkage. It should take only a slight motion of the cam to force the shoes against the drum.

As I posted earlier, mine was not working right, I had it completely disassembled, centered it, and properly adjusted it, now it works fine. It's a very simple setup. Hard to imagine something wrong not being obvious.
2013 Royal Enfield B5
2002 Kawasaki Vulcan 750
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2009 Genuine Stella 2 stroke
1980 Puch Maxi ZA50 2 speed
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Sectorsteve

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Re: rear drum brake being a bit odd
« Reply #17 on: April 28, 2014, 05:37:29 AM »
It happened also to brian (whoguy)
Exactly the same thing same damage. Swing arm plate and all nuts washers and brake plate ruined. I've pulled the swing arm off. Its straight now. My new parts arrived but I've lost all confidence because everytime I think its sorted, it locks up. The faster I'm going the more damage and the more dangerous.
Remember I've done my brake shoes changed sprockets, chains etc on the re and never had this problem before..

lemming:
Sectorsteves motorcycle is the only one I've ever heard of bending the swing arm.  I'm still trying to figure out how that could possibly happen by just using the rear brake.  There isn't that much torque on the rear brake even if the rear wheel is locked up.

If the rear brake shoes are adjusted correctly, the coil spring on the rear brake lever will automatically disengage the rear brake as soon as the riders foot releases the pressure on the brake pedal.
Don't worry about it but remember, the front brake on your motorcycle does over 80 percent of the braking.
Several racers I know only use the rear brake to keep the rear of the bike from coming around under heavy braking.  (I'm talking about 120 mph down to 20 mph for a sharp turn).

whoguy

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Re: rear drum brake being a bit odd
« Reply #18 on: April 28, 2014, 09:48:14 AM »
Yes it did... I believe the original washer and pin(bolt) is a relatively soft metal and can deform from overtightening (the wider than needed slot doesn't help either)... and can allow the drum assembly to rotate slightly and cause the drum brake to lock on.

The pin, washer and nut should be high tensile metal... or aircraft grade I reckon.
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lemming

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Re: rear drum brake being a bit odd
« Reply #19 on: April 28, 2014, 02:10:18 PM »
Fortunately for me, a simple adjustment was sufficient to substantially improve the braking power. It is now capable of actually locking the rear wheel, though I backed it off a little so that takes a bit more oomph to accomplish. When adjusted as described above- tighten until the wheel stops, then back off until it moves free- it seemed a little over-quick to lock. So I backed off a couple turns, and it has good feel now. Strong, but not insta-lock. Thanks, all for putting up with my n00b-itude! You are most helpful!
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