Scary drum brake problem

[aum108]

Hi all,

Bit of a disturbing issue with the rear (drum) brake on my Yamaha Virago XV250.

If I keep off the brake pedal when stopped at intersections, the rear brake works fine - the usual low to medium Virago stopping power, no surprises.

But if I push the brake pedal while stopped, it seems to "give way" and lets me easily push it down a couple of extra inches. After this, once I take off, if I hit the pedal the rear brake suddenly grabs hard.

If this sudden grabbing happens on a poor road surface, the rear wheel locks up. Not enjoyable when slowing down from 80km/h on a wet road, to have the rear wheel fishtailing and the bike threatening to throw me off with a line of cars up my butt.

But if this grabbing happens on a good road surface, I hear a loud metallic "click", the brake suddenly grabs really hard, but goes back to normal.

Either way, after just one "rear wheel grabbing" incident, the brake rights itself and it doesn't happen again, not unless I again push the pedal while stopped.

I took the rear wheel off today to inspect. The shoes are relatively new, with about 3-4mm surface. There seems to be no damage to the drum. The caliper lever readily moves both shoes outward.

I can't think of any reason why the brakes would feel normal under the pedal when I'm moving, but when stopped the pedal just sinks, and the next braking action suddenly grabs the wheel.

My workaround is to never push the brake pedal while stopped. But I'd rather get it right. This is a potentially very dangerous issue, and I need to get it sorted.

Can anyone offer any clues?

Cheers
Dave

[HenryDorsetCase]

Pull the wheel and look at your brake shoes. I et they are worn. (assumingyou have checked the obvious like the cable and the adjuster lever)

[paturoa]

This can happen when the diameter of the hub that the shoes press against gets too large (it wears over time just like the shoes). The actuator between the shoes rotates around past the flat part and locks on. Have a google session and find the max diameter of the hub and measure that.

[FJRider]

Pull the wheel and look at your brake shoes. I et they are worn. (assumingyou have checked the obvious like the cable and the adjuster lever)

The rear brakes of bikes with rear drum brakes are usually actuated by a direct rod from the brake pedal to the lever on the back wheel. In the case of Virago's ... I stand to be corrected. The likely cause could be possibly delamination of the brake pads from the brake shoes.

To the OP ..

ANY issue such as you describe should be checked out by those qualified to do so.

Continued use without getting it checked out is stupid. It may even kill you.

[aum108]

The rear brakes of bikes with rear drum brakes are usually actuated by a direct rod from the brake pedal to the lever on the back wheel. In the case of Virago's ... I stand to be corrected. The likely cause could be possibly delamination of the brake pads from the brake shoes.

Ok, I'll get a new pair of shoes from eBay and give those a shot.
I doubt it's the drum, the bike has only 32,000km on it.

To the OP ..
ANY issue such as you describe should be checked out by those qualified to do so.
Continued use without getting it checked out is stupid. It may even kill you.

Thanks for your concern. Normally I would just pass it on to the mechanic. But I'm very tight for cash, and can't afford the $200,$300,$500... the mechanics here in Hamilton would charge.
I need the bike to commute to work. The car would cost an extra $50/week in petrol, which I also can't afford.
I just have to get the bike up to spec on a shoestring.
As I said before, I can bypass any threats by keeping my foot off the brake pedal when stopped.

Cheers
Dave

[FJRider]

Ok, I'll get a new pair of shoes from eBay and give those a shot.
I doubt it's the drum, the bike has only 32,000km on it.


Thanks for your concern. Normally I would just pass it on to the mechanic. But I'm very tight for cash, and can't afford the $200,$300,$500... the mechanics here in Hamilton would charge.
I need the bike to commute to work. The car would cost an extra $50/week in petrol, which I also can't afford.
I just have to get the bike up to spec on a shoestring.
As I said before, I can bypass any threats by keeping my foot off the brake pedal when stopped.

Cheers
Dave

For a start ... check the amount of travel the brake pedal has. How far does the lever on the spline at the back wheel travel .. from foot off the pedal till brake resistance is felt. (measure at the connection point the lever/cable makes contact with the lever)
And how long since the rear pads were replaced ??? Remember ... internal expanding brake shoes do not wear evenly over the entire length/surface of the brake pad.

My advice ... take the back wheel to a workshop and ask what the problem is. And go from there.

My concern is for the poor sod that may have to take avoiding action to avoid hitting you. And either injure themselves ... and/or ... damage their vehicle in the process.

[Laava]

I have had similar with brake shoes that are just too far gone. Stop at the lights, rear brake stays locked. Have to reach back with toes to push lever back.

[aum108]

Just today I changed the brake shoes, and the sudden snatching on the back brake no longer happens. Huge improvement.

But what I get is this:

1. If I only use the brake pedal when moving, the rear brake works normally, no issues
2. If I push down the brake pedal when stopped, it goes spongy and sinks down another 3-4cm. The next time I use the rear brake when moving, I hear a metallic click, and then the brake behaves normally without the menacing grabbing that was happening before. Subsequent uses of the brake pedal while moving give normal response. But if I use the brake pedal when stopped, the whole cycle starts all over again - first use when moving gives a loud click, then the brake behaves normally

I haven't measured the inside diameter of the drum, but I'm really wondering with a bike that's done only 30,000km how likely this really is to be an issue.

Does anyone have any more thoughts?

Cheers
Dave

[Laava]

Just that. You need to measure the inside of the drum. If PO rode the rear brake, it could be flogged. You need to check it!

[Banditbandit]

Check also that the actuator that sits between the shoes is the right size and fit ... and is working properly ... it sounds like it is rotating too far (why the pedal sinks a few more centimetres) and then clicking back ito place ...

Check it all out anyway ... and good luck commuting ... I hope the rear brake works when you need it most ...

[Drew]

The brake torque arm is loose I bet.

[imdying]

Take the drum and shoes to Waikato Brake and Clutch Specialists, they'll measure it up and check they're not mismatched. I'm pretty sure they're still one of the best bonders around, so if the drum is oversize they'll probably be able to bond up an oversize set. Assuming you've checked the obvious things suggested. If they do find it oversize but can't (as opposed to won't) help with an oversize set, send it to me and I'll sort it out.

[FJRider]

Check also that the actuator that sits between the shoes is the right size and fit ... and is working properly ... it sounds like it is rotating too far (why the pedal sinks a few more centimetres) and then clicking back ito place ...

The seating of the actuator is often the issue.

[Drew]

I'm gonna say it again for effect. Brake torque arm! Sounds to me like when he is stopped with foot on brake, the plate with the pads mounted is rotating the way the actuator arm is pulling it. When he's moving, it can't do that because the braking force is holding it back. Hence the first time he uses the brakes after he's been stopped, the braking force pulls it back to the full extent the torque arm allows and makes the brakes grab.

Keep it simple stupid, then look at the hard shit. Has the bike had a new tyre recently? Or the back wheel out for anything at all?

[rok-the-boat]

Get someone else to press the pedal while you look closely at the mechanism on the back wheel and all the other associated bits. My guess it is an external problem. Maybe the lever that attaches to the splines is not tight enough on the splines and it slips around a bit. Certainly sounds odd.


After thought:
Does it have a cable or a rod?
Has it always been like this or did it start suddenly?
Are the spings on the shoes fitted correctly?