Drum brakes intermittently grabbing?

[ebrammer252]

I picked up a used Axis M200 (CT200U-EX rebrand) and everything is working well except the rear drum brake.

Riding it this past weekend and coming down a hill giving it a little bit of slowing brake the bike would grab, let go, grab, let go, etc.

Thought it might be the shoes so I grabbed a new set and just installed them. Cleaned up the inside of the housing with brake clean, greased the pivot points, greased the shaft etc. Same result

If I back out the ferrule on the end of the brake cable until it spins freely, I have very little braking power (and it still grabs and gives repeatedly). If I turn the ferrule in to get better braking power the wheel (off the ground in the garage) can be spun and then locks up, move it by hand and it'll loosen up again and repeat

What am I missing here?

 

[sparkwizard]

Do you have a way to check the drum for runout? It sounds like it is not round.

 

[ebrammer252]

Do you have a way to check the drum for runout? It sounds like it is not round.

I don't unfortunately. Is this a common occurrence that this happens? Do I just need to source a new rear wheel?

 

[Augiedoggie]

Pressed drums will distort easily. Remove wheel and brake and check drum runout. You can sometimes mount wheel/drum without brake hub on bike or put axle in vise with wheel drum and spin wheel slowly. Fasten a dowel or rod with clamp or vise grip to braking surface of drum and rotate slowly while watching for changes in clearance. Dial indicator is more accurate test but most DIY guys can get reasonably good accuracy with crude method suggested

 

[DaddyJohn]

Something I’ve found on the CT200’s is the drum can rust on just one side if it’s sat parked outdoors for some amount of time. This is because when the bike is leaning on the kickstand, the drum is in the perfect position to collect water and let it sit. Not saying that’s your problem necessarily, but it could be someone’s grabby brake issue if they don’t get in and clean it out.

 

[Minimichael]

I get a similar problem where the shoes feel stuck after depressing the hand lever to a full stop. They can feel halfway engaged still when I then go to accelerate, UNLESS I roll the bike backwards an inch or so and maybe blip the lever just a touch before throttling again. Something about rolling back seems to let the shoes fully retract? Your situation sounds somewhat similar and while I don't have a solution for you I was wondering if it might be solved with stiffer shoe springs.

 

[ebrammer252]

So to provide an update here. I bought a new wheel thinking that the drum hub on my OE wheel was warped. New wheel does the exact same thing

Any other ideas?

 

[Minimichael]

Is your hand lever under enough return tension to disengage when you let go? Is your wheel axle sliding around in the swing arm bolt slots? Are your axle diameter and brake drum hole i.d. a close fit?

 

[ebrammer252]

Yeah, the hand lever returns to extended no issues.no the wheel is secure and yeah everything is a nice solid fit, no sloppiness.

 

[sparkwizard]

Have you checked either one of your drums for runout?

 

[ebrammer252]

Have you checked either one of your drums for runout?

I haven't, I don't have a dial indicator to check them unfortunately.

 

[sparkwizard]

Raise the back wheel. Tape a crayon to the frame, barely touching the drum. Spin the wheel.
Sharpie marker works, too, but crayon wax is easier to remove from the drum.
A dial indicator might have been cheaper than that new wheel.

 

[Minimichael]

Raise the back wheel. Tape a crayon to the frame, barely touching the drum. Spin the wheel.
Sharpie marker works, too, but crayon wax is easier to remove from the drum.
A dial indicator might have been cheaper than that new wheel.

Might be able to see just by spinning and watching. Tho what are the chances both wheels have similar out of roundness?

 

[Minimichael]

Maybe it's something other than your brake.

 

[sparkwizard]

Might be able to see just by spinning and watching. Tho what are the chances both wheels have similar out of roundness?

Both came from same Chinese factory, I'd say chances of two defects might be good.
But you are correct in looking at the big picture. Maybe something else. OP should see if a tire is egg shaped when spinning it off the ground.
When we say "try known good part", we mean a used part that did not exhibit the same problem, not another new part from the same place.

 

[ebrammer252]

Maybe it's something other than your brake.

What else could it be though? My next thought is to try a new drum brake assembly.

 

[ebrammer252]

Here's a video of the new rim spinning in the vise. You can see that the wheel itself has some poor manufacturing (outside lip of wheel), as are all of them it seems. But the drum brake hub is straight with no wobble.

https://streamable.com/2u3oyi

 

[sparkwizard]

Is there any paint or other contamination on your brake shoes? Or inside the drums?

 

[ebrammer252]

Is there any paint or other contamination on your brake shoes? Or inside the drums?

Nope, this was happening on the shoes the bike came with. To be sure I bought a brand new pair, same result.

 

[sparkwizard]

This will make no sense at all, but it is what I would try.
Ride the bike, while holding the throttle open, drag the brake at the same time. Get the shoes and drum really hot, like until you can smell it.
Let it cool and try again. What can you lose? Maybe the shoes are moving in and out in the drum.
"Burn them in".