Topic: Death by drum break

[maliveline]

My drum brakes have always been overly responsive since I've had my bike. I tried loosening the nut that allows more play in my rear break pedal but all that did is make my rear break pedal kinda sloppy. basically my rear break has 2 options.

1: press to light and get no response at all

2: press just a little and the back wheel locks up.

I found myself in a jam on the highway a few weeks back where I had to stop fast and
my knee jerk reaction was to hit my brakes firmly. The back wheel locked up on damp rough pavement and I started fish tailing at 50 mph and almost laid my bike down. Needless to say I haven't had my heart rate up that high for a long time.

[vames]

Have you thought about maybe fixing it? Just asking.

[maliveline]

why do you guys think it would be like that? I have no idea when the breaks were changed last. do you think it could be this way because the brakesare new or something and need to be worn in?

[mlinder]

I rarely even use my rear brake. Even a crappy, 1/3 working back brake will lock up with almost no effort.

Are you sure it's working incorrectly?

[Duke McDukiedook]

Nah, mine like to lock up if you press too hard, wet or dry.

That is why disc brakes are on more expensive or newer anything, they are better.

[MCRider]

What bike is it?

More likely the shoes are old, though even with a lot of material on them, if they've been abused they can get glazed and hard, and lose a progressive feel. Replacement is the only fix.

Also, try this: Loosen the axle slightly, enough that its not pinching the brake plate. Have someone push down on the brake pedal hard and hold it. This will center the brake plate in the drum. Now tighten the axle. This should restore some progressiveness to the feel. If the plate is not centered you have much less of the shoe hitting the drum giving it an all or nothing feel.

But you may still need shoes.

This is what it takes to make a drum work right. Used to be done all the time, now its vintage and expensive. I've had it done on my project but I'm not running yet.
http://www.racetech.com/HTML_FILES/BrakeArcing.html

[CycleRanger]

More likely the shoes are old, though even with a lot of material on them, if they've been abused they can get glazed and hard, and lose a progressive feel. Replacement is the only fix.

Yep.  New shoes.  Also the drum is probably glazed as well.  Run a little emery cloth around the inside to break the glaze.

[dave500]

a broken return spring can allow the drum to pick up the shoe and "self energise" too much.

[vames]

Only way you'll know is to take it apart. It's really easy, and if something's broken it will be obvious. If not, you should at least clean it all out, deglaze the drum (or replace if it's effed), replace the shoes, put it back together and set it to spec.

Despite what others are saying, lock/no-lock are not the only two modes of the rear brake. Granted they're not discs, but they are designed help stop the bike without crashing.

[MCRider]

More likely the shoes are old, though even with a lot of material on them, if they've been abused they can get glazed and hard, and lose a progressive feel. Replacement is the only fix.

Yep.  New shoes.  Also the drum is probably glazed as well.  Run a little emery cloth around the inside to break the glaze.

Good point. And blow the ton of brake dust out (but stand back because it will be VERY dirty, do it outside). Pull the cam out and clean everything. Nothing like a good clean brake.

[MCRider]

The CB750 rear brake can have a good feel (not on/off) and be effective if set up properly. IMO

[singedebile]

I rarely even use my rear brake. Even a crappy, 1/3 working back brake will lock up with almost no effort.

were you using your front brake at all? it really should be your first resort..  if you tap the rear brake lightly to load up the front end then use the 90% front brake to stop

[mlinder]

I rarely even use my rear brake. Even a crappy, 1/3 working back brake will lock up with almost no effort.

were you using your front brake at all? it really should be your first resort..  if you tap the rear brake lightly to load up the front end then use the 90% front brake to stop

Eh what?

As I said, I rarely even use my rear brake. Which means I primarily use my front brakes.

I find engine braking for initial transfer of balance to be safer, more reliable, and all around better.

[TwoTired]

Doesn't the 72 Cb750 Have a rear brake wear indicator like the 74 CB550?

[MCRider]

I know the early ones did not, don't know when they appeared, K2 or 3+.

Nevertheless it won't show if the shoes are glazed.

[TwoTired]

OK then, I want to know what the relative position of the lever arm is to the actuating rod.  It ought to start out a about a 90 degree angle.

There is a post inside with two flats.  The lever arm rotates that post, which expands the shoes into the drum.  When the shoes wear, the post must be turned more making it easier to apply more pressure to the drum and get a lock up.

An earlier post was spot on.  Rear brake needs maintenance.  While you should be able to lock the rear brake, it should be easily modulated, even when wet.

Of course, a panic'd user can lock it up, but it should also turn free when released.  If not, it's broke and needs fixing.

Cheers,

[gane]

Double check your' brake stay arm... As I recall, both ends should use shoulder bolts & fit snugly. any movement there can allow the torque from braking to cause hub to shift & bing, eratic braking...G

[Don R]

The friction material can losen also, get in there and check it before something worse happens.

[Mainerider]

As other have said, a rear drum is a pretty simple mechanical item to get working properly. More importantly, though, is to work on your braking technique.  Regardless of whether the rear is a disc or drum, hard braking will result in weight transfer OFF of the rear wheel and onto the front; the lack of tire loading is what causes the rear wheel to lock; under hard braking there simply isn't enough downward pressure to "push" the tire contact patch into the pavement.

Because of this, your front brake should be the one you reach for; an initial light squeeze to load the front tire and then a progressively stronger application. It's also a great habit to train yourself to "cover" the front brake lever when riding in order to shave off another 1/2 second or so of reaction time.

With the exception of low speed (like parking lot) tight turning and trail-braking, you're best to completely ignore the rear brake.  A few bikes, namely heavy cruisers/tourers with long wheelbases that act like fulcrums, can make good use of the rear brake but by and large that old line about "having to lay her down" almost always translates into " I panicked, stomped on the rear as hard as I could, locked it up and low-sided" .  For proper braking techniques, Nick Lenatch's "Sport Bike Riding Techniques" book is a great reference and applies to all types of bikes. Ride safe.

[Nortstudio]

I'm rebuilding a rear wheel.  What the best way to get all the glaze out of the drum?  Is brake cleaner good enough, or should it be lightly Wet/dry sanded?

Many thanks.

[CycleRanger]

I'm rebuilding a rear wheel.  What the best way to get all the glaze out of the drum?  Is brake cleaner good enough, or should it be lightly Wet/dry sanded?

Many thanks.

I just use a bit of ~180-240 grit emery cloth dry. Sand lightly around the drum just to scuff it up.
New shoes really do make a difference.  I suspect there's a lot of these bikes still rolling with 35+ year old shoes.

[Nortstudio]

I'm rebuilding a rear wheel.  What the best way to get all the glaze out of the drum?  Is brake cleaner good enough, or should it be lightly Wet/dry sanded?

Many thanks.

I just use a bit of ~180-240 grit emery cloth dry. Sand lightly around the drum just to scuff it up.
New shoes really do make a difference.  I suspect there's a lot of these bikes still rolling with 35+ year old shoes.

Thanks so much.

[754]

 Brake dust.. not only dirty.. may be toxic with OEM pads.

  first thing drop the wheel with tire on, on its side, drum down, Give a few raps carefully helps to get the major.. but not all dust out..

[Nortstudio]

Gottcha.  I bought the hard core mask (and have plenty of rubber gloves) for doing this when I first changed the brakes on my 1961 Vespa.  I had been told to be aware of the possibility of asbestos - which would almost certainly be in there.  Pads from the era, even if they had been changed, may have been the asbestos type, since it was such an old bike.

Thanks for the heads up.

[Retro Rocket]

I rarely even use my rear brake. Even a crappy, 1/3 working back brake will lock up with almost no effort.

were you using your front brake at all? it really should be your first resort..  if you tap the rear brake lightly to load up the front end then use the 90% front brake to stop

Eh what?

As I said, I rarely even use my rear brake. Which means I primarily use my front brakes.

I find engine braking for initial transfer of balance to be safer, more reliable, and all around better.

Yep, hard on the front whilst going down gears, using your rear brake to stop in a panic situation will get you killed. I witnessed a guy panic brake on a Harley with rear brake only ,  he hit an out board motor on the back of a boat, the leg of the motor split him down the middle and he died on the side of the road, he was doing less than 30MPH......Learn to use your front brake correctly, it could save your life....