Rear brake pedal vibrating; drum brakes?

Hi all,
My 1980 KZ 440 LTD model A has recently been acting weird when I apply the rear brakes. (they are drums; it's old so no ABS...)

There is a violent vibration when I press hard on the brake pedal, i.e. when I push it all the way down with force. If I only do a little, no vibration presents itself.
The thing is, this occurrence is random. Sometimes the rear brake pedal is fine, other times it will vibrate like crazy. I immediately release my foot on the rear brake pedal when this happens.
I have been nervous to test and find out when it occurs and what happens if I hold it down.
I haven't noticed if the rest of the bike shakes, but this could be because, as I said before, I immediately let go of the brake pedal.

Research found:
1) I feel like if it were a warped rotor I would be having the vibration every time I press the rear brake pedal down, no?
2) I have read online about the swing arm brushes, but again, wouldn't I feel the vibrating every time?
3) I've read cleaning the brake assembly could help...but this feels more serious than that. I don't know
4) I will check later that the wheel axle is tight.

The reasons I am not convinced by the above solutions is because of how random and how violent the vibration is. It really feels like something is just not right, or came, loose? Is that possible??? When it happens it is so loud you can hear it like a jackhammer or something. Crazy!

Any help is appreciated! I will of course check the above 1-4 to be safe.

Have you adjusted the chain recently? On my 650 after adjusting the chain I have to press the rear brake to seat it back to the drum, then tighten everything down. I'm just wondering if vibration could be caused by not doing this, and having the shoes and drum not seated correctly? It may be best to take the wheel off and take a look inside.

Drums don't have rotors. I believe the drum is part of the wheel hub. It think if it were warped you would feel it all the time. However, you might want to change the brake shoes, MartinCSR (sorry, I forgot how to spell your name) has had them come apart in the wheel, locking the wheel up. The brake lining is actually glued onto the metal and if they are original they are likely to separate, atleast thats what I've gathered so far. Its an age thing, not a mileage.

That spelling is close enough. hee. .newkzrider18, if you don't know the age of the brake shoes, replace them. As Matt mentioned, a lining can separate from a shoe >> the adhesive gets old & brittle. There's no telling what you'll find, but my rear brake had been operating completely normally, then one day when rolling the bike off the center stand, the rear wheel locked. The 25+ yr old originals looked fine except for the lining coming off, so you can't tell by looking at them.

The old parts have asbestos, so don't use compressed air or breathe the dust. I wiped down everything w clean cloths saturated w denatured alcohol. Others had reported brake squeal w new aftermarket brake shoes, so I sanded the leading edges of the new shoes & sanded the glaze off the drum >> very evenly & carefully to minimize dust & wiping often w solvent. I guess you'll need to inspect the drum for damage. mine looked good except for the glazing. Use brake caliper grease where applicable & don't get it on the friction surfaces.
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oh wow I feel stupid. right. why did I even mention rotors...sorry!
I know how disk brakes vs drum brakes work. I change them on my '95 truck. I feel quite embarrassed hahaha. I assume they would operate the same on a motorcycle too.

I will look at the drum brakes then! Pretty scary though that they can lock up

Now you know & after installing new brake shoes, there shouldn't be any worries. Related, you should also make certain the Front brake is good. If your bike still has the old old old original brake lines, you should replace them. old rubber lines can burst, but I've never had that happen.

Hi guys, quick question before taking it apart. How would one know when it is time to change the drum itself? Changing the shoes is easy, but what are examples of not-so-obvious red flags that the drum, and therefore the entire wheel, need replacing?

newkzrider18 wrote: ........... How would one know when it is time to change the drum itself? ............

Take a look in the Kawasaki Service Manual for your exact year/model bike. It will tell you the service limit for the inside diameter of the drum. Ed

When you get it apart, take some good pics for future reference. Besides following the Kawasaki service manual, if the mileage is low, then I would think the drum should be well within the service limits. Anything out of the ordinary should be obvious: the brake pedal vibration leads me guess that some gouging of the surface is within the realm of possibility, but maybe not. you won't know until you take a look.


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If anyone was curious, here is what I found.
For starters everything was under the service limit. The drum diameter, the lining thickness, spring length, brake camshaft diameter.
Also there’s a big crack leading from the outside to the inside.

Looks like that is jacked up in just about every possible way.
Glad it didn't grenade while you were riding it.

Wow, that could've been deadly. Looks like the side of the shoe was rubbing against the drum too.